Engine

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

Severity: medium Drive with care, to a shop

What P0391 means

The engine control module compares the bank 2 camshaft position sensor "B" signal with the crankshaft sensor signal. If the pulses arrive at the wrong time or have the wrong shape, it sets P0391. "B" is usually the exhaust camshaft on bank 2, but this varies by manufacturer. The cause may be the sensor, its wiring, or camshaft timing that has drifted.

Symptoms

  • Check engine light on
  • Rough idle or misfires
  • Hesitation and reduced power
  • Hard starting or no start
  • Higher fuel consumption
  • Occasional stalling

Possible causes

  1. Failed camshaft position sensor "B"
  2. Damaged wiring or poor connector contact
  3. Stretched timing chain or misaligned timing belt
  4. Damaged or dirty reluctor/tone wheel
  5. Oil or metal debris on the sensor
  6. Faulty variable valve timing phaser
  7. Rarely, an ECM input circuit fault

How to diagnose

  1. Scan for codes and freeze frame data, and look for other timing or misfire codes
  2. Inspect the sensor, connector and harness for chafing, corrosion and oil
  3. Test sensor power, ground and signal wires with a multimeter per the wiring diagram
  4. Compare camshaft and crankshaft signals with a scope
  5. Remove the sensor and inspect its tip and the tone wheel
  6. Check cam timing and chain or belt wear using marks and scan tool data
  7. Check VVT phaser operation and oil pressure
  8. Clear the code and confirm it does not return

Common fixes

  • Replace camshaft position sensor "B"
  • Repair the wiring or replace the connector
  • Replace the timing chain, belt or tensioners and reset timing
  • Replace the tone wheel or VVT phaser
  • Repair or replace the ECM (very rare)

Questions and answers

What does P0391 mean?

The ECM found that the bank 2 camshaft sensor "B" signal does not match what it expects. The sensor, wiring or camshaft timing may be at fault.

Can I drive with P0391?

Only briefly and carefully, to a shop. The engine may stall, and a timing problem can lead to serious engine damage.

Will replacing the sensor fix it?

Not always. Check the wiring, connector and timing chain or belt first, or the code will likely return.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.