P0391 medium Severity

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

May cause check engine light illumination, rough idle, hesitation, reduced power, and possible no‑start or stalling conditions.

Overview

OBD‑II trouble code P0391 indicates an out‑of‑range or performance issue with the camshaft position sensor "B" circuit on engine bank 2, often linked to sensor signal errors, wiring faults, timing discrepancies, or related component failures.

Common Symptoms

  • Illuminated check engine light
  • Rough idle or misfire on bank 2
  • Hesitation or reduced engine power
  • Difficulty starting or no start condition
  • Increased fuel consumption

Most Common Causes

Faulty camshaft position sensor "B" high

Sensor fails to provide correct signal to the PCM, triggering the code.

Wiring harness damage or connector issues high

Corroded, frayed, or shorted wiring can distort the sensor signal.

Timing chain/belt out of specification medium

Mechanical timing misalignment affects sensor signal relative to crankshaft position.

Faulty reluctor/tone wheel medium

Damaged or misaligned reluctor can produce erratic sensor readings.

PCM/ECM input circuit failure low

Less common cause where control module misinterprets sensor data.

Diagnostic Steps

  1. Connect an OBD‑II scanner and confirm presence of P0391; check for related codes.
    Expected: P0391 appears, possibly with other cam/crank sensor codes.
    Interpretation: Confirms issue is present in camshaft sensor B circuit.
  2. Perform a visual inspection of camshaft sensor B wiring and connectors.
    Expected: No broken wires, corrosion, or loose connectors.
    Interpretation: If issues found, repair may resolve the code.
  3. Test camshaft position sensor B signal with multimeter/scan tool
    Expected: Sensor output within manufacturer specifications (voltage range).
    Interpretation: Out‑of‑spec signal indicates sensor or wiring fault.
  4. Check engine mechanical timing (chain/belt alignment and condition).
    Expected: Timing marks aligned per OEM specs.
    Interpretation: If off, correct timing before further testing.
  5. If wiring and sensor are good, test PCM input for proper signal interpretation.
    Expected: PCM reads stable sensor signal.
    Interpretation: Irregular readings suggest PCM input fault.

Repair Solutions

Replace camshaft position sensor B medium
Estimated Cost: $80 - $200

OEM or quality aftermarket sensor recommended; clear codes and retest.

Repair or replace damaged wiring/connectors medium
Estimated Cost: $20 - $150

Ensure good connections and proper insulation.

Correct engine mechanical timing hard
Estimated Cost: $300 - $1000

Labor‑intensive; required if timing chain/belt is stretched or misaligned.

PCM repair or replacement hard
Estimated Cost: $500 - $1500

Consider only after all other causes are ruled out.

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Assuming only crankshaft sensor fault without verifying camshaft sensor circuit
  • Replacing camshaft sensor without checking wiring harness and connectors
  • Ignoring timing chain/belt condition which can influence sensor readings

Frequently Asked Questions

Technical definition of P0391 OBD-II Code

Camshaft Position Sensor "B" Circuit Range/Performance (Bank 2) is the standard definition for P0391. This diagnostic code is triggered when the ECU detects a problem in the Ignition.

Is it safe to drive with a P0391 code?

You should treat P0391 as a medium issue. May cause check engine light illumination, rough idle, hesitation, reduced power, and possible no‑start or stalling conditions.

Common signs of the P0391 error code

Drivers often report: Illuminated check engine light, Rough idle or misfire on bank 2, Hesitation or reduced engine power when this code is present.

Potential causes for OBDII code P0391

It can be caused by several factors, most notably: Faulty camshaft position sensor "B", Wiring harness damage or connector issues, Timing chain/belt out of specification.

What is the price difference for fixing P0391?

It depends on what needs to be fixed. Repair or replace damaged wiring/connectors repairs are cheaper (~$150), while PCM repair or replacement repairs are on the higher end (~$1500).

Does code P0391 apply to Chevrolet vehicles?

Yes, P0391 is a generic code that applies to all OBD-II compliant vehicles, including Ford, Toyota, Honda, Chevrolet, Nissan, Dodge, BMW, and more.

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