Error code

OBD2 P0391

OBD2P0391
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Camshaft Position Sensor 'B' Circuit Range/Performance.

Severity

moderateCan drive, but performance will be poor and fuel efficiency may decrease.

Summary

P0391 indicates an issue with the camshaft position sensor B circuit range or performance on bank 2 of your engine.

Symptoms

  • Hesitation upon acceleration
  • General lack of engine performance
  • Diminished fuel efficiency
  • Overheated catalytic converter due to timing issues
  • Spark detonation (backfire) when decelerating
  • Spark knock (pinging) when accelerating

Common Causes

  • Defective camshaft sensor or crankshaft sensor
  • Open or shorted wiring to the camshaft sensor
  • Corroded or fluid-soaked connector/camshaft sensor
  • Faulty PCM or PCM programming error

Diagnosis

  1. Perform a visual inspection of all system-related wiring harnesses and connectors.
  2. Test voltage and ground signals at the camshaft sensor using a digital volt/ohmmeter (DVOM).
  3. Disconnect the electrical connector from the camshaft sensor and test it for resistance values.
  4. Use an oscilloscope to observe waveform patterns and check for unexpected spikes or glitches.

Fixes

  • Replace defective camshaft position sensor B if necessary.

FAQ

What should I do if my car has P0391?

Start by checking the wiring and connectors for any signs of damage or corrosion. Test the camshaft position sensor B using a DVOM and oscilloscope to determine if it needs replacement.

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

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