Camshaft Position Sensor "B" Circuit Range/Performance (Bank 2)
The PCM detected a signal from the camshaft position sensor B (Bank 2) that is outside the expected voltage or frequency range. This sensor helps the engine computer time fuel injection and ignition precisely, and a faulty signal can cause rough running, reduced power, or starting issues. The vehicle may enter limp mode to protect the engine while you drive to a repair facility.
What You Might Notice
- Check engine light illuminated
- Lack of engine power or acceleration
- No start condition or hard starting
- Engine stalling at idle or while driving
- Rough idle or hesitation during acceleration
Most Common Causes
- 1
Faulty Camshaft Position Sensor B
The sensor itself may be failing electrically or mechanically, sending out-of-range signals to the PCM. This is the most common cause of P0391.
- 2
Poor Wiring Connection at Sensor B
Corroded, loose, or damaged wiring or connectors at the camshaft position sensor B circuit can cause intermittent or incorrect signal voltage.
- 3
Electrical Short or Open Circuit
A broken wire, damaged harness, or short to ground in the sensor B circuit will prevent proper signal transmission to the PCM.
- 4
PCM or Module Communication Fault
Less commonly, the PCM itself may have a fault processing the sensor signal, though sensor and wiring issues are far more typical.
How to Diagnose It
- 1
Check Faulty Camshaft Position Sensor B — The sensor itself may be failing electrically or mechanically, sending out-of-range signals to the PCM. This is the most common cause of P0391.
- 2
Check Poor Wiring Connection at Sensor B — Corroded, loose, or damaged wiring or connectors at the camshaft position sensor B circuit can cause intermittent or incorrect signal voltage.
- 3
Check Electrical Short or Open Circuit — A broken wire, damaged harness, or short to ground in the sensor B circuit will prevent proper signal transmission to the PCM.
- 4
Check PCM or Module Communication Fault — Less commonly, the PCM itself may have a fault processing the sensor signal, though sensor and wiring issues are far more typical.
How to Fix It
- 1
Inspect and Test Camshaft Position Sensor B
Use a multimeter to check the sensor's resistance and voltage output while the engine cranks. Compare to manufacturer specifications for Bank 2. Replace the sensor if readings are out of range.
- 2
Check Wiring and Connectors
Inspect the sensor harness and connector for corrosion, bent pins, loose terminals, or damaged insulation. Clean corroded connectors with electrical contact cleaner and reseat firmly. Repair or replace damaged wiring.
- 3
Test Circuit Continuity and Voltage
Backprobe the sensor connector with a multimeter to verify power supply voltage (typically 5V) and that the signal line is not shorted to ground. Check for open circuits using continuity mode.
- 4
Clear Code and Perform Road Test
After repairs, clear the code with a scan tool and road test the vehicle to confirm the check engine light does not return and power/performance are restored.
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