P0391 Code: Meaning, Symptoms, Causes & Fix

Overview

Symptoms

• hard start when cold
• rough running or misfire
• engine noise or unstable timing

Common causes

• Sensor drift or delayed actuation affecting camshaft position sensor b circuit range/performance (bank 2)
• Mechanical restriction affecting response
• Connector pin damage/corrosion or harness stress near related components

How to diagnose P0391

1. Confirm P0391 and capture freeze-frame data with a professional scan tool.
2. Inspect wiring, connectors, and grounds related to camshaft position sensor b circuit range/performance (bank 2) for obvious defects.
3. Compare commanded vs actual values in live data under the same operating condition.
4. Check for related DTCs to identify the root-cause chain before replacing parts.
5. After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code P0391

High: This code is high severity because the affected system can directly impact drivability, safety, or catalyst/engine protection.

Can you drive with P0391?

Driving with P0391 should be limited to a short trip for diagnosis/repair. Continued driving can cause expensive secondary damage.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

1. Repair obvious wiring/connector faults first to prevent repeat parts replacement.
2. Address the root fault mode (performance) in the camshaft position sensor b circuit range/performance (bank 2) circuit/system.
3. Apply the required relearn/adaptation procedure if specified by service information.
4. Road-test and verify P0391 remains cleared under the conditions that originally set the code.

Fix options

• Clean/repair mechanical restriction where applicable.
• Test component operation against service specs.
• Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$700-$3200

Common mistakes when diagnosing P0391

• Replacing parts without verifying voltage, ground, and signal integrity first.
• Ignoring related stored/pending codes that indicate upstream faults.
• Skipping post-repair verification drive cycle and readiness checks.

P0391 in common vehicles

P0391 appears across makes such as BMW, Mercedes-Benz, Audi, Volvo. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes P0391?

P0391 is commonly set by performance faults affecting camshaft position sensor b circuit range/performance (bank 2).

How much does it cost to fix P0391?

For P0391, repair costs are typically $700-$3200 depending on exact root cause, labor rates, and part quality.

Can I clear P0391 without repair?

You can clear P0391 temporarily, but the code usually returns until the underlying fault is corrected.

Helpful tools

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