P0390 – Camshaft Position Sensor “B” Circuit Bank 2

P0390 is an OBD-II trouble code that points to a problem with the camshaft position sensor “B” on Bank 2. In plain English, your engine computer is not happy with the signal it’s getting from one of the cam sensors on the side of the engine that does not contain cylinder #1. This can cause hard starting, rough running, and poor fuel economy. The fix might be as simple as a bad sensor or wiring, but it can also indicate deeper timing or engine issues if ignored.

What Does P0390 Mean?

P0390 stands for “Camshaft Position Sensor ‘B’ Circuit (Bank 2).” Your ECU uses camshaft position sensors to know exactly where the camshafts are in relation to the crankshaft. That timing information is critical for fuel injection and ignition.

When the ECU sees an incorrect, missing, or unstable signal from the Bank 2 “B” cam sensor, it sets P0390 and usually turns on the check engine light. On many engines, “B” refers to the exhaust camshaft sensor, but always check your service information for your specific vehicle.

Quick Reference

• Code: P0390
• Meaning: Camshaft Position Sensor “B” Circuit Malfunction – Bank 2
• Severity: Moderate – can lead to drivability problems and stalling
• Common Fixes: Replace cam sensor, repair wiring, correct timing issues
• Systems Affected: Engine performance, fuel economy, starting

Real-World Example / Field Notes

In the shop, I see P0390 most often on higher-mileage V6 and V8 engines where heat and oil have cooked the cam sensor and its connector. A typical case: a customer comes in with a check engine light, occasional long crank, and rough idle when hot. Scan tool shows P0390 and maybe a random misfire code. Scope testing reveals a noisy or flat cam signal on Bank 2 “B.” Replacing the sensor and repairing a brittle harness section usually brings the engine right back to normal, especially if the timing chain and guides are still in good shape.

Symptoms of P0390

• Check engine light on: P0390 is usually stored as a confirmed fault, not just pending.
• Hard starting or no-start: The ECU may struggle to sync fuel and spark without a clean cam signal.
• Rough idle: Unstable timing control can make the engine shake or surge at idle.
• Loss of power: Variable valve timing (VVT) may be disabled, reducing performance.
• Poor fuel economy: The engine may run richer and less efficiently when timing is off.
• Engine stalling: In some cases, the engine can stall coming to a stop or at idle.
• Misfire or hesitation: You may feel misfires, hesitation, or jerking under acceleration.

Common Causes of P0390

Most Common Causes

• Failed camshaft position sensor “B” (Bank 2): Internal electronics fail from age, heat, or oil contamination.
• Damaged wiring or connector at the sensor: Broken wires, corroded pins, or loose terminals interrupt the signal.
• Oil contamination in the connector: Leaking valve cover gaskets can let oil wick into the connector and cause signal issues.
• Incorrect sensor installation: After engine work, the wrong sensor type or improper seating can cause P0390.
• Timing chain or belt stretch/misalignment: If mechanical timing is off, the cam signal won’t match what the ECU expects.

Less Common Causes

• Faulty crankshaft position sensor: The ECU compares crank and cam signals; a bad crank sensor can make the cam look “wrong.”
• Internal ECU fault: Rare, but a failing engine computer can misread a good cam signal.
• Damaged camshaft reluctor/trigger wheel: Bent, cracked, or missing teeth will distort the sensor’s signal.
• Aftermarket remote start or wiring mods: Poorly installed electronics can interfere with sensor power or ground circuits.
• Severe sludge or debris at the sensor tip: Metal shavings or sludge buildup can weaken the sensor’s ability to read the cam.

Diagnosis: Step-by-Step Guide

You’ll want a basic scan tool, a digital multimeter, and ideally a wiring diagram. A lab scope is great for pros, but most DIYers can get far with a meter and visual inspection. Always work with the engine off when unplugging connectors, and disconnect the battery if you’re repairing wiring.

1. Confirm the code: Use a scan tool to verify P0390 is present. Check for related cam/crank or VVT codes that might point to a broader issue.
2. Check freeze-frame data: Note engine RPM, load, and temperature when P0390 set. This helps you reproduce the conditions.
3. Visual inspection of Bank 2 sensor “B”: Locate the cam sensor on Bank 2 (often the rear or firewall side on V engines). Check for cracked housings, oil-soaked connectors, or broken retainers.
4. Inspect wiring and connector: Look for chafed insulation, melted sections near exhaust components, and green corrosion at the pins. Gently tug each wire to find hidden breaks.
5. Check sensor power and ground: With key on, back-probe the connector (refer to a wiring diagram) and verify proper 5V reference and good ground using a multimeter.
6. Test signal circuit: With the sensor plugged in and engine cranking or running, check for a pulsing signal voltage on the signal wire. A lab scope will show a square wave; a meter should show fluctuating voltage.
7. Swap sensors (where possible): On some engines, you can swap Bank 1 and Bank 2 “B” sensors. If the code moves to the other bank, the sensor is likely bad.
8. Check mechanical timing: If sensors and wiring check out, verify timing chain/belt alignment. Look for excessive slack, broken guides, or misaligned timing marks.
9. Advanced scan data: Use live data or Mode $06 to compare camshaft timing values and correlation tests between banks.
10. ECU evaluation: Only after all other tests pass should you suspect the ECU. Confirm power, ground, and continuity before replacing it.

Pro tip: Don’t just clear P0390 and throw in a new sensor. Spend a few minutes inspecting the harness and connector. Fixing a $5 broken wire can save you from burning up a brand-new $80 sensor.

Possible Fixes & Repair Costs

Most P0390 repairs are straightforward once you pinpoint the cause. Common fixes include replacing the Bank 2 camshaft position sensor “B,” repairing or replacing damaged wiring/connectors, cleaning oil-contaminated plugs, and correcting timing chain or belt issues. Typical repair costs at a shop range from about $120–$300 for a sensor replacement, $150–$400 for wiring repairs depending on access, and $700–$1,800 or more if timing components need to be replaced. Labor rates, vehicle design, and parts quality (OEM vs aftermarket) all affect the final cost.

Can I Still Drive With P0390?

In many cases, you can still drive with P0390, but it’s not ideal. Some vehicles will start and run with reduced power and poor fuel economy, while others may stall unexpectedly. If you notice hard starting, rough idle, or stalling, you should avoid long trips and heavy traffic until it’s diagnosed. Driving short distances to a repair shop is usually fine, but towing is smarter if the engine is cutting out or refusing to start.

What Happens If You Ignore P0390?

Ignoring P0390 can turn a relatively small electrical issue into a bigger mechanical or safety problem. Long-term mis-timed fuel and spark can foul spark plugs, damage catalytic converters, and increase fuel consumption. If the root cause is a stretched timing chain or failing guides, you risk serious internal engine damage if they let go. It’s best to address the code sooner rather than later.

Related Sensor Camshaft Codes

Compare nearby sensor camshaft trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P0365 – Camshaft Position Sensor “B” Circuit Bank 1
• P0385 – Crankshaft Position Sensor “B” Circuit
• P0335 – Crankshaft Position Sensor “A” Circuit
• P0394 – Camshaft Position Sensor “B” Circuit Intermittent Bank 2
• P0393 – Camshaft Position Sensor “B” Circuit High Bank 2
• P0392 – Camshaft Position Sensor “B” Circuit Low Bank 2

Key Takeaways

• P0390 points to a problem with the Bank 2 camshaft position sensor “B” circuit, often the exhaust cam sensor.
• Common causes are a bad sensor, damaged wiring, oil-contaminated connectors, or timing issues.
• Symptoms range from a simple check engine light to hard starting, rough idle, and loss of power.
• Most fixes are affordable if caught early; ignoring the code can lead to more expensive engine repairs.
• Proper diagnosis with a scan tool and basic electrical checks is the best way to avoid unnecessary parts replacement.

Vehicles Commonly Affected by P0390

P0390 shows up most often on V6 and V8 engines where there are multiple cam sensors and banks. It’s commonly seen on Ford and Lincoln 3.5L/3.7L and 5.4L engines, GM V6/V8s (Chevrolet, GMC, Cadillac), and many Toyota and Lexus V6 models. Nissan and Infiniti VQ-series V6 engines, Hyundai and Kia V6s, and some Honda/Acura V6s can also set this code. Any modern multi-cam, multi-bank engine with variable valve timing can experience P0390 when sensors, wiring, or timing components start to age.

FAQ

Can I clear P0390 and keep driving if the car feels fine?

You can clear the code, but if the underlying problem is still there, P0390 will usually return. Even if the car feels okay now, the issue can worsen and lead to hard starting, stalling, or catalytic converter damage. It’s better to diagnose and fix it rather than repeatedly clearing the code.

Is P0390 caused by low oil level?

Low oil level doesn’t directly trigger P0390, but it can contribute. Low or dirty oil affects variable valve timing operation and can cause extra wear or heat around the cam sensors. If your oil is very low or sludged, correct that first, then recheck for codes and symptoms.

How do I know which side is Bank 2 for P0390?

Bank 2 is the side of the engine that does not contain cylinder #1. On many transverse V6 engines, Bank 2 is the rear bank near the firewall, but not always. The best way is to check a factory service manual or a reliable repair database for your specific engine layout.

Can a bad crankshaft sensor cause P0390?

Yes, it can. The ECU constantly compares camshaft and crankshaft signals. If the crank sensor is failing or its signal is noisy, the ECU may think the cam signal is out of sync and set cam-related codes like P0390. That’s why it’s important to look at both sensors during diagnosis.

How urgent is it to fix P0390?

You usually don’t need to stop driving immediately, but you shouldn’t postpone the repair for long. If you’re experiencing hard starting, stalling, or major power loss, treat it as urgent and get it checked right away. Fixing P0390 early is cheaper and safer than waiting for related damage to show up.