P0391 - Camshaft Position Sensor B Circuit Range/Performance (Bank 2)
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0391 is an SAE diagnostic trouble code regarding the Camshaft Position Sensor (CMP) B on Bank 2. The 'Range/Performance' designation indicates that the PCM has detected an erratic or irrational signal that does not correlate correctly with the Crankshaft Position Sensor (CKP) signal. While the sensor is technically functioning, the pulse width, frequency, or timing of the signal is outside of the calibrated parameters. This often involves issues with the Variable Valve Timing (VVT) system, mechanical timing misalignment, or excessive electrical interference (EMI) affecting the Hall-effect sensor feedback.
Possible Causes
Faulty Camshaft Position Sensor (internal component failure or magnetic interference)
Incorrect engine oil weight or sludge buildup affecting VVT actuator performance
Wiring harness damage or corroded connectors causing excessive resistance
Mechanical timing issue (stretched timing chain or jumped belt)
Damaged reluctor ring (tone wheel) on the camshaft
Symptoms
Recommended Solution
- Visual Inspection: Check sensor B connector on Bank 2 for oil contamination or corrosion. Ensure engine oil is at the correct level and viscosity.
- Voltage Testing: Use a multimeter to verify reference voltage (typically 5V) and a clean ground. Signal wire should show a clean toggle between low and high when the engine is turned manually.
- Oscilloscope Analysis: Compare CMP and CKP waveforms to check for timing correlation and signal integrity. Look for rounded 'square' waves or dropouts.
- Replacement: Replace the Camshaft Position Sensor if electrical tests fail. If timing is off mechanically, inspect timing chain tensioners and VVT solenoids.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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