P0391 Camshaft Position Sensor B Circuit Range/Performance (Bank 2)

P0391 points to a range or performance issue in Camshaft Position Sensor B circuit on Bank 2. The Bank 2 cam B signal is present but implausible.

Code details

Generic OBD-II · P0

System: Ignition / Misfire
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the Bank 2 cam sensor before checking timing, oil control, and cam target integrity.

Symptoms of P0391

Rough idle, shaking, or a stumble under acceleration.
A flashing check-engine light during an active misfire.
Power loss and higher fuel consumption.

Common causes of P0391

Worn spark plugs, ignition coils, or plug wires.
Fuel-delivery problems — injectors, pressure, or a lean/rich mixture.
Vacuum leaks, low compression, or a mechanical fault in that cylinder.

Useful checks before replacing parts

Compare Bank 2 cam B timing, crankshaft correlation, VVT command versus actual movement, oil condition, freeze-frame RPM, and correlation codes.
Inspect sensor mounting, cam target alignment, timing chain or belt condition, phaser behavior, wiring resistance, and connector fit.
Check whether the signal becomes implausible during startup, hot idle, acceleration, deceleration, or VVT actuation.

Related OBD-II codes

These nearby ignition / misfire entries can help compare wording and pin down the fault area.