Code
P0389
Generic
P — Powertrain
Crankshaft Position Sensor B Circuit Intermittent
AI status
Completed
Completed
100%
Causes
- Damaged, corroded, or loose connector at CKP sensor B
- Broken, chafed or shorted wiring harness between sensor and PCM/ECU
- Intermittent internal failure of the crankshaft position sensor (sensor B)
- Poor ground or reference voltage for the sensor circuit
- Reluctor ring damage, missing teeth, or excessive air gap that intermittently disrupts the signal
- Intermittent PCM/ECU input fault or poor connector at the PCM
Symptoms
- Intermittent illumination of MIL (Check Engine Light)
- Intermittent rough idle, stumbling, or misfire
- Hard starting or occasional no-start conditions
- Intermittent stalling while idling or during driving
- Reduced engine performance or limp mode on some vehicles
- Diagnostic trouble codes related to CKP B or related misfire/correlation codes
What to check
- Retrieve freeze frame and repair history with a scan tool; note RPM, load and engine temp when code set
- Clear codes then road-test and re-check; try to reproduce with various engine loads and temperatures
- Visually inspect sensor B connector and harness for damage, corrosion, or water entry
- Wiggle harness and connector while monitoring live sensor data on scan tool to look for intermittent signal changes
- Backprobe sensor connector and confirm reference voltage, ground, and signal presence with key ON/crank
- Use an oscilloscope to capture the sensor waveform while cranking and at idle/drive to confirm waveform continuity and shape
Signal parameters
- Hall-effect (3-wire) sensor: reference ~5 V (vehicle-specific), signal is square wave toggling roughly 0–5 V; frequency varies with RPM
- Magnetic/VR sensor: AC sine wave; amplitude increases with RPM (typical tens of mV at cranking to volts at high rpm)
- Typical frequency proportional to engine speed; no steady signal or complete dropouts indicate intermittent/open/short
- Expected idle frequency and amplitude are vehicle specific — compare to known-good waveform or factory spec
Diagnostic algorithm
- Scan vehicle for codes and record freeze-frame data; note conditions when P0389 set
- Visually inspect CKP sensor B, connector, and adjacent wiring for damage, oil/water contamination, corrosion, or loose mounting
- Securely clean and reseal any corroded connectors; repair broken or exposed wires (do not use temporary tape only)
- Backprobe connector and verify reference voltage and ground with key ON; if missing, trace wiring to PCM for open or short
- Use an oscilloscope to observe the CKP B waveform while cranking and running; look for signal dropouts, noise, or inconsistent amplitude
- Perform a wiggle test on the harness and connectors while monitoring the waveform to reproduce the intermittent behavior
- Measure resistance/continuity of sensor circuit to PCM; check for short to battery or ground
- If wiring and connectors are confirmed good and waveform inconsistent, replace CKP sensor B and retest
- If new sensor still intermittent, inspect reluctor ring/trigger wheel and engine timing components for damage or movement
- If all external checks are good, consider PCM/ECU input fault and inspect PCM connector and grounds; consult manufacturer procedures before PCM replacement
Likely causes
- Connector corrosion or bent terminals at sensor B
- Wire broken internally where harness flexes (common at engine mount or near firewall)
- Sensor B failing under temperature/vibration but passes static resistance checks
- Reluctor ring loosened or debris on ring causing sporadic signal loss
Fault status
Status
P0389 — Crankshaft Position Sensor B Circuit Intermittent. ECU detected intermittent or lost signal from CKP sensor B circuit. May cause MIL, misfires, hard starting, or stalling. Investigate sensor, wiring, connectors, reluctor ring, and PCM inputs.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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Code
P0389
GWM
P — Powertrain
- Crankshaft Position Sensor B Malfunction
AI status
Completed
Completed
100%
Causes
- Damaged, corroded, or loose connector at CKP sensor B
- Broken, chafed or shorted wiring harness between sensor and PCM/ECU
- Intermittent internal failure of the crankshaft position sensor (sensor B)
- Poor ground or reference voltage for the sensor circuit
- Reluctor ring damage, missing teeth, or excessive air gap that intermittently disrupts the signal
- Intermittent PCM/ECU input fault or poor connector at the PCM
Symptoms
- Intermittent illumination of MIL (Check Engine Light)
- Intermittent rough idle, stumbling, or misfire
- Hard starting or occasional no-start conditions
- Intermittent stalling while idling or during driving
- Reduced engine performance or limp mode on some vehicles
- Diagnostic trouble codes related to CKP B or related misfire/correlation codes
What to check
- Retrieve freeze frame and repair history with a scan tool; note RPM, load and engine temp when code set
- Clear codes then road-test and re-check; try to reproduce with various engine loads and temperatures
- Visually inspect sensor B connector and harness for damage, corrosion, or water entry
- Wiggle harness and connector while monitoring live sensor data on scan tool to look for intermittent signal changes
- Backprobe sensor connector and confirm reference voltage, ground, and signal presence with key ON/crank
- Use an oscilloscope to capture the sensor waveform while cranking and at idle/drive to confirm waveform continuity and shape
Signal parameters
- Hall-effect (3-wire) sensor: reference ~5 V (vehicle-specific), signal is square wave toggling roughly 0–5 V; frequency varies with RPM
- Magnetic/VR sensor: AC sine wave; amplitude increases with RPM (typical tens of mV at cranking to volts at high rpm)
- Typical frequency proportional to engine speed; no steady signal or complete dropouts indicate intermittent/open/short
- Expected idle frequency and amplitude are vehicle specific — compare to known-good waveform or factory spec
Diagnostic algorithm
- Scan vehicle for codes and record freeze-frame data; note conditions when P0389 set
- Visually inspect CKP sensor B, connector, and adjacent wiring for damage, oil/water contamination, corrosion, or loose mounting
- Securely clean and reseal any corroded connectors; repair broken or exposed wires (do not use temporary tape only)
- Backprobe connector and verify reference voltage and ground with key ON; if missing, trace wiring to PCM for open or short
- Use an oscilloscope to observe the CKP B waveform while cranking and running; look for signal dropouts, noise, or inconsistent amplitude
- Perform a wiggle test on the harness and connectors while monitoring the waveform to reproduce the intermittent behavior
- Measure resistance/continuity of sensor circuit to PCM; check for short to battery or ground
- If wiring and connectors are confirmed good and waveform inconsistent, replace CKP sensor B and retest
- If new sensor still intermittent, inspect reluctor ring/trigger wheel and engine timing components for damage or movement
- If all external checks are good, consider PCM/ECU input fault and inspect PCM connector and grounds; consult manufacturer procedures before PCM replacement
Likely causes
- Connector corrosion or bent terminals at sensor B
- Wire broken internally where harness flexes (common at engine mount or near firewall)
- Sensor B failing under temperature/vibration but passes static resistance checks
- Reluctor ring loosened or debris on ring causing sporadic signal loss
Fault status
Status
P0389 — Crankshaft Position Sensor B Circuit Intermittent. ECU detected intermittent or lost signal from CKP sensor B circuit. May cause MIL, misfires, hard starting, or stalling. Investigate sensor, wiring, connectors, reluctor ring, and PCM inputs.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
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Code
P0389
HUMMER
P — Powertrain
Crankshaft Position Sensor B Circuit Intermittent
AI status
Completed
Completed
100%
Causes
- Damaged, corroded, or loose connector at CKP sensor B
- Broken, chafed or shorted wiring harness between sensor and PCM/ECU
- Intermittent internal failure of the crankshaft position sensor (sensor B)
- Poor ground or reference voltage for the sensor circuit
- Reluctor ring damage, missing teeth, or excessive air gap that intermittently disrupts the signal
- Intermittent PCM/ECU input fault or poor connector at the PCM
Symptoms
- Intermittent illumination of MIL (Check Engine Light)
- Intermittent rough idle, stumbling, or misfire
- Hard starting or occasional no-start conditions
- Intermittent stalling while idling or during driving
- Reduced engine performance or limp mode on some vehicles
- Diagnostic trouble codes related to CKP B or related misfire/correlation codes
What to check
- Retrieve freeze frame and repair history with a scan tool; note RPM, load and engine temp when code set
- Clear codes then road-test and re-check; try to reproduce with various engine loads and temperatures
- Visually inspect sensor B connector and harness for damage, corrosion, or water entry
- Wiggle harness and connector while monitoring live sensor data on scan tool to look for intermittent signal changes
- Backprobe sensor connector and confirm reference voltage, ground, and signal presence with key ON/crank
- Use an oscilloscope to capture the sensor waveform while cranking and at idle/drive to confirm waveform continuity and shape
Signal parameters
- Hall-effect (3-wire) sensor: reference ~5 V (vehicle-specific), signal is square wave toggling roughly 0–5 V; frequency varies with RPM
- Magnetic/VR sensor: AC sine wave; amplitude increases with RPM (typical tens of mV at cranking to volts at high rpm)
- Typical frequency proportional to engine speed; no steady signal or complete dropouts indicate intermittent/open/short
- Expected idle frequency and amplitude are vehicle specific — compare to known-good waveform or factory spec
Diagnostic algorithm
- Scan vehicle for codes and record freeze-frame data; note conditions when P0389 set
- Visually inspect CKP sensor B, connector, and adjacent wiring for damage, oil/water contamination, corrosion, or loose mounting
- Securely clean and reseal any corroded connectors; repair broken or exposed wires (do not use temporary tape only)
- Backprobe connector and verify reference voltage and ground with key ON; if missing, trace wiring to PCM for open or short
- Use an oscilloscope to observe the CKP B waveform while cranking and running; look for signal dropouts, noise, or inconsistent amplitude
- Perform a wiggle test on the harness and connectors while monitoring the waveform to reproduce the intermittent behavior
- Measure resistance/continuity of sensor circuit to PCM; check for short to battery or ground
- If wiring and connectors are confirmed good and waveform inconsistent, replace CKP sensor B and retest
- If new sensor still intermittent, inspect reluctor ring/trigger wheel and engine timing components for damage or movement
- If all external checks are good, consider PCM/ECU input fault and inspect PCM connector and grounds; consult manufacturer procedures before PCM replacement
Likely causes
- Connector corrosion or bent terminals at sensor B
- Wire broken internally where harness flexes (common at engine mount or near firewall)
- Sensor B failing under temperature/vibration but passes static resistance checks
- Reluctor ring loosened or debris on ring causing sporadic signal loss
Fault status
Status
P0389 — Crankshaft Position Sensor B Circuit Intermittent. ECU detected intermittent or lost signal from CKP sensor B circuit. May cause MIL, misfires, hard starting, or stalling. Investigate sensor, wiring, connectors, reluctor ring, and PCM inputs.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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