Code
P0388
Generic
P — Powertrain
Crankshaft Position Sensor B Circuit High
Views:
UK: 33
EN: 73
RU: 42
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on CKP B signal wire
- Open or high-resistance ground or reference circuit
- Failed/cracked/crushed crankshaft position sensor (Bank B)
- Corroded or loose connector pins
- Damaged wiring harness (chafing, pinched, rodent damage)
- Oil/contaminant on sensor or tone wheel affecting signal
Symptoms
- Check Engine Light (MIL) illuminated with P0388 stored
- Engine may crank but not start or be difficult to start
- Intermittent no-start or stalling
- Rough idle, misfires or reduced power under load
- Reduced fuel economy or limp-home mode on some vehicles
- Erratic tachometer or no tach signal
What to check
- Read and record DTC(s) and freeze frame with a scan tool; note conditions when code set
- Inspect sensor connector and wiring for damage, corrosion, bent pins, or oil intrusion
- Visually inspect CKP tone wheel/reluctor for missing teeth, heavy debris or damage
- Check battery voltage and chassis/engine grounds for good connections
- Backprobe sensor connector and monitor signal with a multimeter (DC volts) or better with an oscilloscope
- Perform a wiggle test on wiring while monitoring live data for intermittent changes
Signal parameters
- Hall-effect (most modern CKP): square-wave signal ~0–5 V (logic high ~4.5–5 V, logic low ~0–0.5 V); 'circuit high' typically >4.5 V when it should toggle
- VR (magnetic) type: AC amplitude varies with rpm; low-speed amplitude ~0.05–1.0 Vrms, increasing with engine speed; DC offset should not be present
- Reference power (if sensor requires power) typically 5 V regulated or ignition-switched 12 V depending on design—check OEM specs
- Pulse frequency proportional to engine RPM; at idle expect pulses corresponding to number of teeth/revolutions on tone wheel
- When cranking, pulses should appear; a steady high voltage with no pulses suggests short/high condition
Diagnostic algorithm
- Confirm P0388 and any companion codes using a scan tool; record freeze-frame and live CKP B data.
- Visually inspect CKP B sensor, connector, and harness near the sensor and along the engine/transmission path for damage/corrosion/oil.
- With key ON engine OFF, backprobe the sensor connector: measure reference voltage (if present) and ground integrity. Compare to OEM spec.
- Monitor the CKP B signal while cranking with an oscilloscope if possible. Look for proper square wave (Hall) or AC waveform (VR). Note if voltage is stuck high.
- If signal is high with key ON but engine OFF, disconnect the sensor and re-measure at the harness. If the voltage disappears when sensor disconnected, suspect harness or PCM supply/ground; if it remains, suspect PCM.
- Check continuity from sensor connector pins to PCM pins for signal, reference, and ground; look for short to battery (measure resistance to battery +) and short to ground.
- Perform wiggle test on harness and connectors while monitoring live data to find intermittent faults.
- Replace sensor with a known-good or OEM part if wiring checks good and sensor out of spec. Re-test.
- If wiring and sensor are good but high circuit persists, inspect/replace connector terminals or repair wiring. If still present, suspect PCM fault and verify before replacement (confirm with bench/secondary tests or dealer PCM check).
- Clear codes and test drive under the conditions that set the code to verify repair. Document repairs and retest.
Likely causes
- Damaged signal wire shorted to constant 12V (most common for 'circuit high')
- Failed hall-effect CKP sensor stuck high
- Corroded connector at sensor or ECM causing high resistance and voltage reading errors
- Aftermarket sensor or incorrect replacement with wrong reference voltage type
- PCM internal fault (less common)
Fault status
Status
P0388 is set when the engine control module detects the Crankshaft Position Sensor B signal voltage is higher than expected (typically indicating a short to battery or stuck-high sensor output). Inspect sensor, wiring/connectors, and the PCM supply/grounds; repair or replace the faulty component and verify with live data.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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Code
P0388
GWM
P — Powertrain
- High Sensor Position B Crankshaft Position
Views:
UK: 26
EN: 47
RU: 29
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on CKP B signal wire
- Open or high-resistance ground or reference circuit
- Failed/cracked/crushed crankshaft position sensor (Bank B)
- Corroded or loose connector pins
- Damaged wiring harness (chafing, pinched, rodent damage)
- Oil/contaminant on sensor or tone wheel affecting signal
Symptoms
- Check Engine Light (MIL) illuminated with P0388 stored
- Engine may crank but not start or be difficult to start
- Intermittent no-start or stalling
- Rough idle, misfires or reduced power under load
- Reduced fuel economy or limp-home mode on some vehicles
- Erratic tachometer or no tach signal
What to check
- Read and record DTC(s) and freeze frame with a scan tool; note conditions when code set
- Inspect sensor connector and wiring for damage, corrosion, bent pins, or oil intrusion
- Visually inspect CKP tone wheel/reluctor for missing teeth, heavy debris or damage
- Check battery voltage and chassis/engine grounds for good connections
- Backprobe sensor connector and monitor signal with a multimeter (DC volts) or better with an oscilloscope
- Perform a wiggle test on wiring while monitoring live data for intermittent changes
Signal parameters
- Hall-effect (most modern CKP): square-wave signal ~0–5 V (logic high ~4.5–5 V, logic low ~0–0.5 V); 'circuit high' typically >4.5 V when it should toggle
- VR (magnetic) type: AC amplitude varies with rpm; low-speed amplitude ~0.05–1.0 Vrms, increasing with engine speed; DC offset should not be present
- Reference power (if sensor requires power) typically 5 V regulated or ignition-switched 12 V depending on design—check OEM specs
- Pulse frequency proportional to engine RPM; at idle expect pulses corresponding to number of teeth/revolutions on tone wheel
- When cranking, pulses should appear; a steady high voltage with no pulses suggests short/high condition
Diagnostic algorithm
- Confirm P0388 and any companion codes using a scan tool; record freeze-frame and live CKP B data.
- Visually inspect CKP B sensor, connector, and harness near the sensor and along the engine/transmission path for damage/corrosion/oil.
- With key ON engine OFF, backprobe the sensor connector: measure reference voltage (if present) and ground integrity. Compare to OEM spec.
- Monitor the CKP B signal while cranking with an oscilloscope if possible. Look for proper square wave (Hall) or AC waveform (VR). Note if voltage is stuck high.
- If signal is high with key ON but engine OFF, disconnect the sensor and re-measure at the harness. If the voltage disappears when sensor disconnected, suspect harness or PCM supply/ground; if it remains, suspect PCM.
- Check continuity from sensor connector pins to PCM pins for signal, reference, and ground; look for short to battery (measure resistance to battery +) and short to ground.
- Perform wiggle test on harness and connectors while monitoring live data to find intermittent faults.
- Replace sensor with a known-good or OEM part if wiring checks good and sensor out of spec. Re-test.
- If wiring and sensor are good but high circuit persists, inspect/replace connector terminals or repair wiring. If still present, suspect PCM fault and verify before replacement (confirm with bench/secondary tests or dealer PCM check).
- Clear codes and test drive under the conditions that set the code to verify repair. Document repairs and retest.
Likely causes
- Damaged signal wire shorted to constant 12V (most common for 'circuit high')
- Failed hall-effect CKP sensor stuck high
- Corroded connector at sensor or ECM causing high resistance and voltage reading errors
- Aftermarket sensor or incorrect replacement with wrong reference voltage type
- PCM internal fault (less common)
Fault status
Status
P0388 is set when the engine control module detects the Crankshaft Position Sensor B signal voltage is higher than expected (typically indicating a short to battery or stuck-high sensor output). Inspect sensor, wiring/connectors, and the PCM supply/grounds; repair or replace the faulty component and verify with live data.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
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Code
P0388
HUMMER
P — Powertrain
Crankshaft Position Sensor B Circuit High Input
Views:
UK: 23
EN: 59
RU: 29
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on CKP B signal wire
- Open or high-resistance ground or reference circuit
- Failed/cracked/crushed crankshaft position sensor (Bank B)
- Corroded or loose connector pins
- Damaged wiring harness (chafing, pinched, rodent damage)
- Oil/contaminant on sensor or tone wheel affecting signal
Symptoms
- Check Engine Light (MIL) illuminated with P0388 stored
- Engine may crank but not start or be difficult to start
- Intermittent no-start or stalling
- Rough idle, misfires or reduced power under load
- Reduced fuel economy or limp-home mode on some vehicles
- Erratic tachometer or no tach signal
What to check
- Read and record DTC(s) and freeze frame with a scan tool; note conditions when code set
- Inspect sensor connector and wiring for damage, corrosion, bent pins, or oil intrusion
- Visually inspect CKP tone wheel/reluctor for missing teeth, heavy debris or damage
- Check battery voltage and chassis/engine grounds for good connections
- Backprobe sensor connector and monitor signal with a multimeter (DC volts) or better with an oscilloscope
- Perform a wiggle test on wiring while monitoring live data for intermittent changes
Signal parameters
- Hall-effect (most modern CKP): square-wave signal ~0–5 V (logic high ~4.5–5 V, logic low ~0–0.5 V); 'circuit high' typically >4.5 V when it should toggle
- VR (magnetic) type: AC amplitude varies with rpm; low-speed amplitude ~0.05–1.0 Vrms, increasing with engine speed; DC offset should not be present
- Reference power (if sensor requires power) typically 5 V regulated or ignition-switched 12 V depending on design—check OEM specs
- Pulse frequency proportional to engine RPM; at idle expect pulses corresponding to number of teeth/revolutions on tone wheel
- When cranking, pulses should appear; a steady high voltage with no pulses suggests short/high condition
Diagnostic algorithm
- Confirm P0388 and any companion codes using a scan tool; record freeze-frame and live CKP B data.
- Visually inspect CKP B sensor, connector, and harness near the sensor and along the engine/transmission path for damage/corrosion/oil.
- With key ON engine OFF, backprobe the sensor connector: measure reference voltage (if present) and ground integrity. Compare to OEM spec.
- Monitor the CKP B signal while cranking with an oscilloscope if possible. Look for proper square wave (Hall) or AC waveform (VR). Note if voltage is stuck high.
- If signal is high with key ON but engine OFF, disconnect the sensor and re-measure at the harness. If the voltage disappears when sensor disconnected, suspect harness or PCM supply/ground; if it remains, suspect PCM.
- Check continuity from sensor connector pins to PCM pins for signal, reference, and ground; look for short to battery (measure resistance to battery +) and short to ground.
- Perform wiggle test on harness and connectors while monitoring live data to find intermittent faults.
- Replace sensor with a known-good or OEM part if wiring checks good and sensor out of spec. Re-test.
- If wiring and sensor are good but high circuit persists, inspect/replace connector terminals or repair wiring. If still present, suspect PCM fault and verify before replacement (confirm with bench/secondary tests or dealer PCM check).
- Clear codes and test drive under the conditions that set the code to verify repair. Document repairs and retest.
Likely causes
- Damaged signal wire shorted to constant 12V (most common for 'circuit high')
- Failed hall-effect CKP sensor stuck high
- Corroded connector at sensor or ECM causing high resistance and voltage reading errors
- Aftermarket sensor or incorrect replacement with wrong reference voltage type
- PCM internal fault (less common)
Fault status
Status
P0388 is set when the engine control module detects the Crankshaft Position Sensor B signal voltage is higher than expected (typically indicating a short to battery or stuck-high sensor output). Inspect sensor, wiring/connectors, and the PCM supply/grounds; repair or replace the faulty component and verify with live data.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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