Code
P0377
Generic
P — Powertrain
Timing Reference High Resolution Signal B Too Few Pulses
AI status
Completed
Completed
100%
Causes
- Faulty high-resolution timing sensor (cam or crank position sensor B)
- Damaged or missing teeth on reluctor/encoder wheel (broken, worn, or missing segments)
- Wiring harness damage (open, short to ground/power, or intermittent)
- Corroded/loose sensor connector or poor terminal contact
- Incorrect sensor air gap or mounting (misaligned or physically shifted)
- Timing chain/belt jumped or mechanical timing fault
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Engine starting difficulties or no start
- Rough idle, stalling, or misfires under load
- Poor acceleration and reduced engine performance
- Inconsistent RPM signal (surging or hesitation)
- Possible diagnostic trouble codes for related position sensors or correlation faults
What to check
- Read and record freeze frame and all related DTCs with a scan tool
- Clear codes, attempt to re-create and monitor live data during cranking and running
- Visually inspect sensor and reluctor/trigger wheel for physical damage, missing teeth, debris, or metal shavings
- Check sensor connector for corrosion, bent pins, or loose terminals; perform wiggle test while monitoring
- Measure sensor supply/reference voltage and ground at the connector (if applicable)
- Check wiring continuity and resistance between sensor and PCM; inspect for shorts to ground/power
Signal parameters
- Waveform type: square/digital (Hall/TTL) or sine/AC (variable reluctor), depending on sensor type
- Amplitude: low-voltage logic level for Hall sensors (typically 0.0–5.0 V) or AC amplitude for VR sensors (varies with RPM)
- Pulse count: expected number of pulses per revolution as specified by manufacturer (high-resolution typically many teeth per revolution)
- Frequency: proportional to engine RPM (increases with engine speed)
- Duty cycle/pulse width: consistent pulses with predictable spacing tied to trigger wheel geometry
- Signal integrity: clean, repeatable edges or sinusoid; absence of missing/skipped pulses during crank/run
Diagnostic algorithm
- Retrieve freeze-frame data and all active/pending DTCs; note when the fault occurred (crank vs running).
- Visually inspect sensor B, connector, and trigger wheel for damage, missing teeth, debris, or oil contamination.
- With battery charged, backprobe the sensor connector: verify reference power (if applicable), ground, and signal presence with a DVOM.
- Use an oscilloscope to capture the sensor's waveform during cranking and idle; look for missing pulses, irregular amplitude, distortion, or noise.
- Wiggle wiring and connectors while monitoring signal to find intermittent faults; repair any damaged wiring or terminals.
- Manually rotate engine (by crank bolt) and observe waveform/trigger wheel to confirm tooth count and consistent spacing; check for timing jump or damaged reluctor.
- If waveform and wiring are good but pulses are missing only under certain conditions, inspect for electromagnetic interference sources and verify proper sensor air gap and mounting.
- Replace the sensor or trigger wheel if physical damage or out-of-spec signal is confirmed; recheck codes and live data after repair.
- If problem persists after sensor/trigger/wiring replacement, verify PCM power/ground integrity and consider PCM testing or replacement as a last resort.
Likely causes
- Sensor air gap out of specification or sensor physically damaged
- Reluctor/trigger wheel missing or damaged teeth (physical defect)
- Connector corrosion or pins pushed out causing intermittent connection
- Wiring abrasion where harness flexes, causing intermittent open/short
- Timing component (chain/belt) slipped, changing trigger alignment
Fault status
Status
PCM detected fewer pulses than expected from Timing Reference High Resolution Signal B — signal missing/interrupted or pulse count below manufacturer specification.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
P0377
GWM
P — Powertrain
- The number of pulses of the B timer signal is below the norm
AI status
Completed
Completed
100%
Causes
- Faulty high-resolution timing sensor (cam or crank position sensor B)
- Damaged or missing teeth on reluctor/encoder wheel (broken, worn, or missing segments)
- Wiring harness damage (open, short to ground/power, or intermittent)
- Corroded/loose sensor connector or poor terminal contact
- Incorrect sensor air gap or mounting (misaligned or physically shifted)
- Timing chain/belt jumped or mechanical timing fault
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Engine starting difficulties or no start
- Rough idle, stalling, or misfires under load
- Poor acceleration and reduced engine performance
- Inconsistent RPM signal (surging or hesitation)
- Possible diagnostic trouble codes for related position sensors or correlation faults
What to check
- Read and record freeze frame and all related DTCs with a scan tool
- Clear codes, attempt to re-create and monitor live data during cranking and running
- Visually inspect sensor and reluctor/trigger wheel for physical damage, missing teeth, debris, or metal shavings
- Check sensor connector for corrosion, bent pins, or loose terminals; perform wiggle test while monitoring
- Measure sensor supply/reference voltage and ground at the connector (if applicable)
- Check wiring continuity and resistance between sensor and PCM; inspect for shorts to ground/power
Signal parameters
- Waveform type: square/digital (Hall/TTL) or sine/AC (variable reluctor), depending on sensor type
- Amplitude: low-voltage logic level for Hall sensors (typically 0.0–5.0 V) or AC amplitude for VR sensors (varies with RPM)
- Pulse count: expected number of pulses per revolution as specified by manufacturer (high-resolution typically many teeth per revolution)
- Frequency: proportional to engine RPM (increases with engine speed)
- Duty cycle/pulse width: consistent pulses with predictable spacing tied to trigger wheel geometry
- Signal integrity: clean, repeatable edges or sinusoid; absence of missing/skipped pulses during crank/run
Diagnostic algorithm
- Retrieve freeze-frame data and all active/pending DTCs; note when the fault occurred (crank vs running).
- Visually inspect sensor B, connector, and trigger wheel for damage, missing teeth, debris, or oil contamination.
- With battery charged, backprobe the sensor connector: verify reference power (if applicable), ground, and signal presence with a DVOM.
- Use an oscilloscope to capture the sensor's waveform during cranking and idle; look for missing pulses, irregular amplitude, distortion, or noise.
- Wiggle wiring and connectors while monitoring signal to find intermittent faults; repair any damaged wiring or terminals.
- Manually rotate engine (by crank bolt) and observe waveform/trigger wheel to confirm tooth count and consistent spacing; check for timing jump or damaged reluctor.
- If waveform and wiring are good but pulses are missing only under certain conditions, inspect for electromagnetic interference sources and verify proper sensor air gap and mounting.
- Replace the sensor or trigger wheel if physical damage or out-of-spec signal is confirmed; recheck codes and live data after repair.
- If problem persists after sensor/trigger/wiring replacement, verify PCM power/ground integrity and consider PCM testing or replacement as a last resort.
Likely causes
- Sensor air gap out of specification or sensor physically damaged
- Reluctor/trigger wheel missing or damaged teeth (physical defect)
- Connector corrosion or pins pushed out causing intermittent connection
- Wiring abrasion where harness flexes, causing intermittent open/short
- Timing component (chain/belt) slipped, changing trigger alignment
Fault status
Status
PCM detected fewer pulses than expected from Timing Reference High Resolution Signal B — signal missing/interrupted or pulse count below manufacturer specification.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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Code
P0377
HUMMER
P — Powertrain
Timing Reference High Resolution Signal B Too Few Pulses
AI status
Completed
Completed
100%
Causes
- Faulty high-resolution timing sensor (cam or crank position sensor B)
- Damaged or missing teeth on reluctor/encoder wheel (broken, worn, or missing segments)
- Wiring harness damage (open, short to ground/power, or intermittent)
- Corroded/loose sensor connector or poor terminal contact
- Incorrect sensor air gap or mounting (misaligned or physically shifted)
- Timing chain/belt jumped or mechanical timing fault
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Engine starting difficulties or no start
- Rough idle, stalling, or misfires under load
- Poor acceleration and reduced engine performance
- Inconsistent RPM signal (surging or hesitation)
- Possible diagnostic trouble codes for related position sensors or correlation faults
What to check
- Read and record freeze frame and all related DTCs with a scan tool
- Clear codes, attempt to re-create and monitor live data during cranking and running
- Visually inspect sensor and reluctor/trigger wheel for physical damage, missing teeth, debris, or metal shavings
- Check sensor connector for corrosion, bent pins, or loose terminals; perform wiggle test while monitoring
- Measure sensor supply/reference voltage and ground at the connector (if applicable)
- Check wiring continuity and resistance between sensor and PCM; inspect for shorts to ground/power
Signal parameters
- Waveform type: square/digital (Hall/TTL) or sine/AC (variable reluctor), depending on sensor type
- Amplitude: low-voltage logic level for Hall sensors (typically 0.0–5.0 V) or AC amplitude for VR sensors (varies with RPM)
- Pulse count: expected number of pulses per revolution as specified by manufacturer (high-resolution typically many teeth per revolution)
- Frequency: proportional to engine RPM (increases with engine speed)
- Duty cycle/pulse width: consistent pulses with predictable spacing tied to trigger wheel geometry
- Signal integrity: clean, repeatable edges or sinusoid; absence of missing/skipped pulses during crank/run
Diagnostic algorithm
- Retrieve freeze-frame data and all active/pending DTCs; note when the fault occurred (crank vs running).
- Visually inspect sensor B, connector, and trigger wheel for damage, missing teeth, debris, or oil contamination.
- With battery charged, backprobe the sensor connector: verify reference power (if applicable), ground, and signal presence with a DVOM.
- Use an oscilloscope to capture the sensor's waveform during cranking and idle; look for missing pulses, irregular amplitude, distortion, or noise.
- Wiggle wiring and connectors while monitoring signal to find intermittent faults; repair any damaged wiring or terminals.
- Manually rotate engine (by crank bolt) and observe waveform/trigger wheel to confirm tooth count and consistent spacing; check for timing jump or damaged reluctor.
- If waveform and wiring are good but pulses are missing only under certain conditions, inspect for electromagnetic interference sources and verify proper sensor air gap and mounting.
- Replace the sensor or trigger wheel if physical damage or out-of-spec signal is confirmed; recheck codes and live data after repair.
- If problem persists after sensor/trigger/wiring replacement, verify PCM power/ground integrity and consider PCM testing or replacement as a last resort.
Likely causes
- Sensor air gap out of specification or sensor physically damaged
- Reluctor/trigger wheel missing or damaged teeth (physical defect)
- Connector corrosion or pins pushed out causing intermittent connection
- Wiring abrasion where harness flexes, causing intermittent open/short
- Timing component (chain/belt) slipped, changing trigger alignment
Fault status
Status
PCM detected fewer pulses than expected from Timing Reference High Resolution Signal B — signal missing/interrupted or pulse count below manufacturer specification.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Repair manuals
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