P0391

Universal

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

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The engine computer monitors the Bank 2 Camshaft Position Sensor B signal to track camshaft position and coordinate engine timing. This code means the signal is outside the expected range or does not behave as expected. It can affect starting, running, or engine performance, but the code alone does not prove the sensor has failed.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the engine stalls, runs very poorly, or loses power, stop somewhere safe and arrange an inspection rather than continuing to drive. If the vehicle runs normally, arrange diagnosis soon and watch for worsening symptoms.

Common Symptoms

  • The check-engine light may be on, even if no drivability change is noticeable.
  • Starting may take longer or be difficult if the engine computer cannot reliably use the camshaft position signal.
  • The engine may run unevenly or lose power if timing control is affected.
  • The engine may stall in some cases if the signal becomes unreliable.
  • There may be no noticeable symptoms aside from the stored code.

Common Causes

  • A degraded or damaged Bank 2 Camshaft Position Sensor B may produce an inaccurate or inconsistent signal.
  • A loose, corroded, damaged, or poorly connected sensor connector or wiring may interfere with the signal.
  • Damage or irregularity in the camshaft signal target or related mechanical components may affect the signal pattern.
  • Mechanical camshaft timing or a variable valve timing system problem, where fitted, may cause the observed camshaft position to differ from expected behavior.
  • An engine computer or other circuit fault is possible, but should be considered only after the sensor circuit and related mechanical causes are checked.

Diagnostic Steps

  1. Note whether the check-engine light is steady or flashing and whether the engine stalls, runs roughly, or loses power; stop driving if it becomes unsafe to continue.
  2. With the engine off and cool, visually inspect accessible wiring and connectors associated with the Bank 2 Camshaft Position Sensor B for looseness or obvious damage. Do not pull on wires or disconnect components while the engine is running.
  3. Check the engine oil level using the vehicle's owner information. Correct oil level matters for engine operation and may be relevant to variable valve timing systems, where fitted.
  4. If a scan tool is available, record this and any related codes before clearing anything; related codes can help distinguish a sensor-signal issue from a broader timing or circuit problem.
  5. If the code returns or symptoms are present, have the circuit and camshaft/crankshaft signals tested using vehicle-specific service information rather than replacing a part based on the code alone.

When to Call a Professional

A technician can review related codes and freeze-frame data, check the sensor circuit and connectors, and compare camshaft and crankshaft signals. If the electrical signals are sound, further checks may include mechanical timing and the variable valve timing system, as applicable to the vehicle.

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Commonly Asked Questions

Does P0391 mean the camshaft position sensor must be replaced?

No. It identifies a Bank 2 Camshaft Position Sensor B circuit range/performance condition. Wiring, connectors, signal targets, or mechanical timing can also cause the monitored signal to be out of range or behave unexpectedly.

What does “B” and “Bank 2” identify?

They distinguish a particular camshaft sensor circuit and engine bank. Their exact physical locations depend on the vehicle's engine layout, so use model-, year-, and engine-specific service information.

Can I drive with P0391?

If the engine runs normally, a short trip for diagnosis may be possible, but arrange inspection soon. Do not continue driving if the engine stalls, runs very poorly, or loses power.

How is P0391 distinguished from a wiring or timing problem?

Diagnosis checks the connector and wiring, evaluates the sensor signal, and compares camshaft and crankshaft behavior. If the electrical signals are plausible, a technician may investigate mechanical timing or variable valve timing, where applicable.

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