P0391 – Camshaft Position Sensor “B” Circuit Range/Performance Bank 2

P0391 is an OBD-II trouble code that points to a problem with the camshaft position sensor “B” on Bank 2 of your engine. When this code sets, your engine computer is telling you it’s not happy with the camshaft signal it’s receiving. That can affect timing, power, fuel economy, and even starting. While P0391 doesn’t always mean your engine is about to fail, you shouldn’t ignore it. Understanding what it means, how it feels when driving, and how to diagnose it will help you decide your next steps with confidence.

What Does P0391 Mean?

P0391 stands for “Camshaft Position Sensor ‘B’ Circuit Range/Performance (Bank 2).” In plain language, your ECU is seeing a camshaft signal from the Bank 2 exhaust or secondary cam sensor (often called sensor “B”) that is out of the expected range, erratic, or not synchronized with the crankshaft signal.

Bank 2 is the side of a V6 or V8 engine that does not contain cylinder #1. On many engines, sensor “B” is the exhaust camshaft sensor for that bank. When the signal is weak, noisy, or out of time, the ECU sets P0391 and usually turns on the check engine light.

Quick Reference

• Code: P0391
• Meaning: Camshaft Position Sensor “B” Circuit Range/Performance (Bank 2)
• Common Culprits: Bad cam sensor, wiring issues, timing problems, oil contamination
• Severity: Moderate – can cause drivability issues and long-term engine damage if ignored
• Typical Fixes: Replace cam sensor, repair wiring, correct timing, address oil or VVT issues

Real-World Example / Field Notes

In the shop, I see P0391 a lot on higher-mileage V6 SUVs and trucks. A typical case: a customer comes in with a check engine light, rough idle, and occasional hard starting. Scan tool shows P0391 and maybe a misfire code. Live data reveals the Bank 2 exhaust cam signal dropping out intermittently when the engine warms up. Pulling the sensor shows oil-soaked connectors and brittle wiring near the valve cover. Replacing the cam sensor and repairing the harness usually clears the code and smooths out the idle immediately.

Symptoms of P0391

• Check engine light on: P0391 will almost always trigger the MIL and store a permanent code until repaired.
• Rough idle: Incorrect cam timing feedback can cause unstable idle, shaking, or surging at stoplights.
• Hard starting: The ECU may struggle to sync crank and cam signals, leading to extended cranking or no-start when hot.
• Loss of power: You may notice sluggish acceleration, especially under load or at higher RPM.
• Poor fuel economy: Incorrect valve timing and fuel delivery can reduce MPG over time.
• Engine hesitation or stumble: Intermittent cam signal dropouts can cause brief misfires or hesitation.
• Occasional stalling: In more severe cases, the engine may stall when coming to a stop or during low-speed driving.

Common Causes of P0391

Most Common Causes

• Failed camshaft position sensor “B” (Bank 2): The sensor itself often fails internally, especially from heat and age, causing weak or erratic output voltage.
• Damaged wiring or connectors: Melted insulation, broken wires, corroded pins, or oil-soaked connectors near the valve cover are very common.
• Timing chain or belt wear: Excessive slack, jumped timing, or a worn tensioner can cause the cam and crank signals to be out of sync.
• VVT (variable valve timing) issues: A sticking VVT solenoid or phaser on Bank 2 can move the camshaft to a position the ECU doesn’t expect.
• Low or dirty engine oil: Poor oil quality can affect VVT operation and camshaft timing, especially on engines that rely heavily on oil pressure for cam control.

Less Common Causes

• Faulty crankshaft position sensor: If the crank signal is off, the ECU may think the cam is at fault and set P0391 along with other codes.
• Mechanical camshaft damage: Worn cam lobes, damaged reluctor wheel, or misaligned tone ring can distort the sensor signal.
• ECU software or internal failure: Rare, but a corrupted calibration or failing ECU driver circuit can misinterpret a good sensor signal.
• Aftermarket remote start or wiring add-ons: Poorly installed electronics can introduce noise or voltage drops in the sensor circuit.
• Water intrusion: Flood damage or heavy water exposure can corrode internal wiring harnesses feeding the cam sensor.

Diagnosis: Step-by-Step Guide

You’ll want a basic tool set, a quality OBD-II scan tool (preferably one that can read live data and Mode $06), a digital multimeter, and access to wiring diagrams or service information for your specific vehicle. A lab scope is ideal but not absolutely necessary for a basic home diagnosis.

1. Confirm the code: Connect your scan tool, read all stored and pending codes, and note freeze-frame data. Look for related cam/crank or VVT codes that might point to a bigger timing issue.
2. Visual inspection: Locate the Bank 2 camshaft position sensor “B.” Inspect the connector and wiring for oil contamination, broken clips, chafing, or burns near exhaust components.
3. Check engine oil condition and level: Verify the oil is clean and at the proper level. Old, sludged oil can cause VVT problems that trigger P0391.
4. Wiggle test: With the engine idling and live data up, gently wiggle the harness and connector for the cam sensor. Watch for signal dropouts or sudden changes in RPM or camshaft data.
5. Test sensor power and ground: Using a multimeter, check for proper 5V reference (or specified voltage) and a solid ground at the sensor connector, following your wiring diagram.
6. Check sensor signal: Backprobe the signal wire and look for a changing voltage as the engine runs. A flat line, extreme noise, or no change indicates a bad sensor or wiring issue.
7. Compare cam and crank correlation: Use the scan tool’s data stream or Mode $06 to look at cam/crank correlation or VVT performance. If correlation is off, suspect timing chain, belt, or VVT problems.
8. Inspect timing components (if needed): If you hear chain rattle, see correlation faults, or have high mileage, remove covers as needed to inspect timing marks, guides, and tensioners.
9. Swap test (if applicable): On engines with identical cam sensors on Bank 1 and Bank 2, swap sensors side to side. If the code follows the sensor (becomes a Bank 1 code), the sensor is bad.
10. Clear codes and road test: After repairs or tests, clear the codes and perform a road test with live data to confirm the cam signal is stable and P0391 does not return.

Pro tip: Don’t just throw a cam sensor at it. Spend a few minutes checking wiring and oil condition first. I’ve fixed many P0391 issues with a simple connector repair or oil service on engines with sticky VVT systems.

Possible Fixes & Repair Costs

Most P0391 repairs are straightforward once you pinpoint the cause. Typical fixes include replacing the Bank 2 camshaft position sensor “B,” repairing or replacing damaged wiring/connectors, correcting timing chain or belt issues, cleaning or replacing VVT solenoids, and performing an oil and filter change with the correct grade. At a repair shop, you’re usually looking at about $150–$350 for a sensor and wiring repair, $250–$600 for VVT-related work, and $800–$2,000+ if timing chain or belt replacement is required. Costs vary by vehicle, engine design, labor rates, and parts quality.

Can I Still Drive With P0391?

In many cases, you can still drive with P0391 for a short period, especially if the engine runs fairly smoothly and the only symptom is a check engine light. However, drivability can worsen without warning. If the cam signal drops out completely, you may experience stalling, hard starting, or a no-start condition. Driving long-term with this code can also stress the catalytic converters and other components. If the engine runs rough, stalls, or feels unsafe, park it and tow it to a shop instead of risking further damage.

What Happens If You Ignore P0391?

Ignoring P0391 can turn a relatively simple repair into a much more expensive one. Prolonged timing issues and misfires can overheat and damage catalytic converters, foul spark plugs, and increase fuel consumption. If the root cause is a worn timing chain or failing VVT system, continued driving may lead to severe engine damage or a no-start situation. It’s best to diagnose and repair the issue as soon as you can.

Last updated: February 13, 2026

Vehicles Commonly Affected by P0391

P0391 shows up frequently on modern V6 and V8 engines with variable valve timing. You’ll commonly see it on Ford and Lincoln SUVs and trucks (3.5L/3.7L V6, some V8s), GM vehicles such as Chevrolet and GMC pickups and crossovers (3.6L V6, 5.3L/6.0L V8), Chrysler, Dodge, and Jeep models with Pentastar and HEMI engines, and various Hyundai, Kia, Nissan, and Infiniti V6 engines. It can appear on European brands as well, but it’s especially common where heat, oil leaks, and tight engine bays stress the cam sensors and wiring.