Code
P0338
Generic
P — Powertrain
Crankshaft Position Sensor A Circuit High
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring (short to battery/ignition voltage)
- Corroded, loose or damaged sensor connector or pins
- Failed crankshaft position (CKP) sensor (Hall or VR type)
- Short to an accessory power feed or ignition-switched supply
- Damaged or missing/cracked tone wheel (reluctor) or sensor air gap problem
- PCM/ECU internal fault or poor ground at PCM
Symptoms
- Check Engine Light (MIL) illuminated
- Hard or no-crank start, intermittent starting
- Engine stalls or runs roughly, misfires
- No or irregular tachometer signal
- Reduced engine power or limp mode depending on vehicle
What to check
- Read freeze-frame and live data for CKP signal and related codes (CMP correlation codes).
- Visual inspection of CKP sensor, connector, tone wheel/reluctor and wiring harness for damage or contamination.
- Wiggle test the harness and connector while monitoring live data to reproduce the fault.
- Measure reference supply and ground at the sensor with key ON (engine off).
- Probe signal at sensor and at the PCM pin to check for continuity and compare voltages.
- Use an oscilloscope to verify proper waveform shape, amplitude and timing while cranking/running.
Signal parameters
- Hall-effect (3-wire) CKP: reference typically ~5 V supply, signal is 0–5 V digital square wave. 'High' considered near supply (≈4–5 V), 'Low' near 0 V.
- VR (variable-reluctance, 2-wire) CKP: AC sine/alternating waveform. Amplitude varies with engine speed — small mV at cranking, rising with RPM. No DC reference present.
- Typical diagnostic thresholds: for Hall sensors a persistent signal voltage above expected active level (stuck high) will set a 'circuit high' fault; for VR sensors an unexpected DC offset or very high voltage may indicate short to supply.
- Actual resistance, voltages and waveform characteristics vary by vehicle — consult OEM electrical specifications before declaring out-of-range values.
Diagnostic algorithm
- Retrieve codes and freeze-frame using a scan tool. Note crank and cam rpm readings and any related codes (CMP/CKP correlation).
- Perform a visual inspection of sensor, connector, tone wheel, and wiring for damage, corrosion, oil/debris or rubbing through insulation.
- With ignition ON (engine off) check for reference voltage (if 3-wire Hall type) and good ground at the sensor connector. Reference should be present and stable.
- Measure continuity between sensor signal/ground wires and the PCM pins. Check for shorts to battery (+B) or ignition-switched circuits and shorts to ground.
- Probe the sensor signal while cranking and while the engine runs. Use an oscilloscope to inspect waveform — looking for stuck high DC level, missing pulses, noise, or abnormal amplitude.
- If waveform is abnormal at the PCM but correct at the sensor connector (or vice versa), isolate to harness/connector or PCM respectively. Repair wiring or connector damage discovered.
- If wiring and connectors check good but signal still abnormal, replace the CKP sensor and retest. Reclear codes and verify repair under various operating conditions.
- If fault persists after replacing sensor and repairing harness, bench-test or replace PCM only after confirming all other system items and referencing manufacturer guidance.
Likely causes
- Faulty CKP sensor
- Short to battery/ignition voltage in the sensor signal or reference wire
- Connector corrosion or pin damage at sensor or PCM
- Damaged tone wheel or incorrect sensor air gap
- PCM fault (least common)
Fault status
Status
P0338 stored when the PCM detects the crankshaft position sensor signal is continuously higher than the expected voltage threshold or the signal is out of the expected waveform parameters. The condition may be intermittent; further inspection of sensor, wiring, connectors and PCM is required.
Repair difficulty: Medium
Diagnostic time: 1.0 - 3.0 hours
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Code
P0338
GWM
P — Powertrain
- High reading of crankshaft position sensor A
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring (short to battery/ignition voltage)
- Corroded, loose or damaged sensor connector or pins
- Failed crankshaft position (CKP) sensor (Hall or VR type)
- Short to an accessory power feed or ignition-switched supply
- Damaged or missing/cracked tone wheel (reluctor) or sensor air gap problem
- PCM/ECU internal fault or poor ground at PCM
Symptoms
- Check Engine Light (MIL) illuminated
- Hard or no-crank start, intermittent starting
- Engine stalls or runs roughly, misfires
- No or irregular tachometer signal
- Reduced engine power or limp mode depending on vehicle
What to check
- Read freeze-frame and live data for CKP signal and related codes (CMP correlation codes).
- Visual inspection of CKP sensor, connector, tone wheel/reluctor and wiring harness for damage or contamination.
- Wiggle test the harness and connector while monitoring live data to reproduce the fault.
- Measure reference supply and ground at the sensor with key ON (engine off).
- Probe signal at sensor and at the PCM pin to check for continuity and compare voltages.
- Use an oscilloscope to verify proper waveform shape, amplitude and timing while cranking/running.
Signal parameters
- Hall-effect (3-wire) CKP: reference typically ~5 V supply, signal is 0–5 V digital square wave. 'High' considered near supply (≈4–5 V), 'Low' near 0 V.
- VR (variable-reluctance, 2-wire) CKP: AC sine/alternating waveform. Amplitude varies with engine speed — small mV at cranking, rising with RPM. No DC reference present.
- Typical diagnostic thresholds: for Hall sensors a persistent signal voltage above expected active level (stuck high) will set a 'circuit high' fault; for VR sensors an unexpected DC offset or very high voltage may indicate short to supply.
- Actual resistance, voltages and waveform characteristics vary by vehicle — consult OEM electrical specifications before declaring out-of-range values.
Diagnostic algorithm
- Retrieve codes and freeze-frame using a scan tool. Note crank and cam rpm readings and any related codes (CMP/CKP correlation).
- Perform a visual inspection of sensor, connector, tone wheel, and wiring for damage, corrosion, oil/debris or rubbing through insulation.
- With ignition ON (engine off) check for reference voltage (if 3-wire Hall type) and good ground at the sensor connector. Reference should be present and stable.
- Measure continuity between sensor signal/ground wires and the PCM pins. Check for shorts to battery (+B) or ignition-switched circuits and shorts to ground.
- Probe the sensor signal while cranking and while the engine runs. Use an oscilloscope to inspect waveform — looking for stuck high DC level, missing pulses, noise, or abnormal amplitude.
- If waveform is abnormal at the PCM but correct at the sensor connector (or vice versa), isolate to harness/connector or PCM respectively. Repair wiring or connector damage discovered.
- If wiring and connectors check good but signal still abnormal, replace the CKP sensor and retest. Reclear codes and verify repair under various operating conditions.
- If fault persists after replacing sensor and repairing harness, bench-test or replace PCM only after confirming all other system items and referencing manufacturer guidance.
Likely causes
- Faulty CKP sensor
- Short to battery/ignition voltage in the sensor signal or reference wire
- Connector corrosion or pin damage at sensor or PCM
- Damaged tone wheel or incorrect sensor air gap
- PCM fault (least common)
Fault status
Status
P0338 stored when the PCM detects the crankshaft position sensor signal is continuously higher than the expected voltage threshold or the signal is out of the expected waveform parameters. The condition may be intermittent; further inspection of sensor, wiring, connectors and PCM is required.
Repair difficulty: Medium
Diagnostic time: 1.0 - 3.0 hours
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Code
P0338
HUMMER
P — Powertrain
Crankshaft Position (CKP) Sensor Circuit High Duty Cycle
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring (short to battery/ignition voltage)
- Corroded, loose or damaged sensor connector or pins
- Failed crankshaft position (CKP) sensor (Hall or VR type)
- Short to an accessory power feed or ignition-switched supply
- Damaged or missing/cracked tone wheel (reluctor) or sensor air gap problem
- PCM/ECU internal fault or poor ground at PCM
Symptoms
- Check Engine Light (MIL) illuminated
- Hard or no-crank start, intermittent starting
- Engine stalls or runs roughly, misfires
- No or irregular tachometer signal
- Reduced engine power or limp mode depending on vehicle
What to check
- Read freeze-frame and live data for CKP signal and related codes (CMP correlation codes).
- Visual inspection of CKP sensor, connector, tone wheel/reluctor and wiring harness for damage or contamination.
- Wiggle test the harness and connector while monitoring live data to reproduce the fault.
- Measure reference supply and ground at the sensor with key ON (engine off).
- Probe signal at sensor and at the PCM pin to check for continuity and compare voltages.
- Use an oscilloscope to verify proper waveform shape, amplitude and timing while cranking/running.
Signal parameters
- Hall-effect (3-wire) CKP: reference typically ~5 V supply, signal is 0–5 V digital square wave. 'High' considered near supply (≈4–5 V), 'Low' near 0 V.
- VR (variable-reluctance, 2-wire) CKP: AC sine/alternating waveform. Amplitude varies with engine speed — small mV at cranking, rising with RPM. No DC reference present.
- Typical diagnostic thresholds: for Hall sensors a persistent signal voltage above expected active level (stuck high) will set a 'circuit high' fault; for VR sensors an unexpected DC offset or very high voltage may indicate short to supply.
- Actual resistance, voltages and waveform characteristics vary by vehicle — consult OEM electrical specifications before declaring out-of-range values.
Diagnostic algorithm
- Retrieve codes and freeze-frame using a scan tool. Note crank and cam rpm readings and any related codes (CMP/CKP correlation).
- Perform a visual inspection of sensor, connector, tone wheel, and wiring for damage, corrosion, oil/debris or rubbing through insulation.
- With ignition ON (engine off) check for reference voltage (if 3-wire Hall type) and good ground at the sensor connector. Reference should be present and stable.
- Measure continuity between sensor signal/ground wires and the PCM pins. Check for shorts to battery (+B) or ignition-switched circuits and shorts to ground.
- Probe the sensor signal while cranking and while the engine runs. Use an oscilloscope to inspect waveform — looking for stuck high DC level, missing pulses, noise, or abnormal amplitude.
- If waveform is abnormal at the PCM but correct at the sensor connector (or vice versa), isolate to harness/connector or PCM respectively. Repair wiring or connector damage discovered.
- If wiring and connectors check good but signal still abnormal, replace the CKP sensor and retest. Reclear codes and verify repair under various operating conditions.
- If fault persists after replacing sensor and repairing harness, bench-test or replace PCM only after confirming all other system items and referencing manufacturer guidance.
Likely causes
- Faulty CKP sensor
- Short to battery/ignition voltage in the sensor signal or reference wire
- Connector corrosion or pin damage at sensor or PCM
- Damaged tone wheel or incorrect sensor air gap
- PCM fault (least common)
Fault status
Status
P0338 stored when the PCM detects the crankshaft position sensor signal is continuously higher than the expected voltage threshold or the signal is out of the expected waveform parameters. The condition may be intermittent; further inspection of sensor, wiring, connectors and PCM is required.
Repair difficulty: Medium
Diagnostic time: 1.0 - 3.0 hours
Similar codes
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Manual library for HUMMER
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