Code
P1278
BUICK
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 11
EN: 30
RU: 19
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
CADILLAC
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 17
EN: 32
RU: 22
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
CHEVROLET
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 18
EN: 35
RU: 21
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
CHRYSLER
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 16
EN: 35
RU: 25
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
FORD
P — Powertrain
Cylinder #8 High To Low Side Open
Views:
UK: 18
EN: 34
RU: 23
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
GM
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 12
EN: 31
RU: 24
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
GMC
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 18
EN: 38
RU: 26
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
HUMMER
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 6
EN: 18
RU: 12
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
LINCOLN
P — Powertrain
Cylinder 8 High To Low Side Open
Views:
UK: 14
EN: 32
RU: 21
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
MERCURY
P — Powertrain
Cylinder 8 High To Low Side Open
Views:
UK: 13
EN: 40
RU: 26
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
OLDSMOBILE
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 17
EN: 44
RU: 22
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
Other
P — Powertrain
Cylinder #8 High To Low Side Open
Views:
UK: 13
EN: 33
RU: 21
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
RAM
P — Powertrain
Starter Control Circuit 2 High
Views:
UK: 0
EN: 7
RU: 3
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P1278
SATURN
P — Powertrain
Accelerator Pedal Position Sensor 1 Circuit High Voltage
Views:
UK: 20
EN: 37
RU: 25
AI status
Completed
Completed
100%
Causes
- Short to battery voltage (sensor signal wire tied to Vb)
- Faulty accelerator pedal position (APP) sensor / pedal assembly
- Damaged wiring harness or connector (chafing, corrosion, pin pushed out)
- Poor sensor ground or 5V reference fault
- ECM/PCM input circuit fault or intermittent module issue
- Water intrusion or contamination at pedal connector
Symptoms
- MIL (Check Engine) illuminated
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle response
- Cruise control may be disabled
- Possible inability to accelerate or unpredictable throttle behavior
What to check
- Read and record freeze frame and live PID data for APP sensor 1 and 2 with a scan tool
- Perform visual inspection of pedal assembly, connector, and wiring for damage or corrosion
- Backprobe and measure APP1 signal voltage at connector with key ON (engine off) and across pedal travel
- Check 5V reference and sensor ground at pedal connector
- Wiggle test wiring while monitoring live data to reproduce fault
- Check for related codes (pedal correlation codes, reference voltage codes)
Signal parameters
- Typical system uses 5V reference, a sensor ground, and a signal output to PCM
- APP sensor output range typically about 0.5 V (closed) to ~4.0–4.5 V (wide open) depending on design
- Expected 5V reference ≈ 5.0 V (±0.25 V) at the pedal connector
- Low/short to ground will show near 0 V; high/short to battery will show near battery voltage (~12 V) or above expected signal range
- Correlation between APP1 and APP2 (if present): one increases while the other decreases; large disagreement indicates sensor/pedal fault
Diagnostic algorithm
- Retrieve freeze-frame, live PIDs, and note when code set and whether it is current or historical.
- Visually inspect pedal, harness, and connector for damage, corrosion, water ingress, or loose terminals. Repair obvious issues.
- With key ON (engine OFF), backprobe connector and measure: 5V reference, sensor ground, and APP1 signal voltage. Confirm 5V reference is stable.
- Slowly operate the pedal while watching APP1 and APP2 PIDs (if available). APP1 should vary smoothly within expected range; look for jumps or voltages above expected maximum.
- Perform a wiggle test on the harness and connector while monitoring APP1 for intermittent changes. Repair any chafing or broken wires.
- If APP1 reads above expected range, isolate the circuit: disconnect the pedal connector and measure for short to battery on the signal wire. Repair short to Vb if found.
- If wiring checks good but APP1 remains abnormal when connector connected, replace the accelerator pedal assembly (sensor).
- If replacement pedal does not correct issue, inspect PCM input circuit for damage and consider module diagnosis or replacement per manufacturer guidance.
- After repairs, clear codes and perform a test drive to verify the fault does not recur and that throttle response is normal.
Likely causes
- Open or shorted signal wire between APP sensor 1 and PCM causing voltage to be seen as high
- Failed APP sensor 1 inside the pedal assembly (internal short to Vb or failed electronics)
- Corroded/loose connector or terminal increasing resistance on ground or reference leading to abnormal readings
- 5V reference overvoltage from PCM or harness short to battery
Fault status
Status
Stored when PCM detects APP Sensor 1 signal voltage above allowable threshold. MIL set; vehicle may enter reduced power mode until condition is corrected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Your experience will help others
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Was this AI description helpful?
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👍 Like
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