P0398 – Ignition Coil “Q” Primary/Secondary Circuit

P0398 is an OBD-II trouble code that points to a problem with the camshaft position sensor “B” circuit on Bank 2, specifically an intermittent or out-of-range signal. In simple terms, your engine computer is losing reliable information about camshaft position on one side of the engine. That information is critical for timing fuel injection and ignition. When it goes bad, you can get rough running, poor fuel economy, or no-start conditions. This guide walks you through what P0398 means, common causes, symptoms, diagnosis steps, and typical repair costs.

What Does P0398 Mean?

P0398 stands for “Camshaft Position Sensor ‘B’ Circuit High (Bank 2) – Intermittent/Erratic.” Bank 2 is the side of the engine that does not contain cylinder 1, and sensor “B” usually refers to the exhaust camshaft sensor or the secondary cam sensor on that bank, depending on design.

Your ECU (engine control unit) constantly monitors the camshaft position sensor signal. If it sees voltage or signal patterns that are too high, noisy, or cutting in and out on Bank 2 sensor B, it sets code P0398 and turns on the check engine light. This is often an electrical issue, but mechanical timing or internal engine problems can also trigger it.

Quick Reference

• Code: P0398
• Meaning: Camshaft position sensor “B” circuit high / intermittent (Bank 2)
• Severity: Moderate to high, depending on symptoms
• Typical causes: Bad cam sensor, wiring faults, connector corrosion, timing issues
• Typical fixes: Replace sensor, repair wiring, correct timing, rare ECU repair

Real-World Example / Field Notes

In the shop, I usually see P0398 on higher-mileage V6 and V8 engines with dual cam sensors per bank. One recent case was a mid-2000s SUV that came in with a rough idle and occasional stalling at stoplights. The owner had already replaced spark plugs and coils, but the problem remained. Scan data showed an unstable camshaft signal on Bank 2 exhaust. The connector at the cam sensor was full of oil and green corrosion from a slow valve cover leak. Cleaning the connector, repairing one broken wire, and replacing the sensor cleared the code and smoothed the idle instantly.

Symptoms of P0398

• Check engine light on: The MIL/SES light will almost always be illuminated.
• Rough idle: Engine may shake or idle unevenly, especially when warm.
• Hard starting: Longer crank times or intermittent no-start when the signal drops out.
• Loss of power: Reduced acceleration, sluggish throttle response, or hesitation.
• Poor fuel economy: Incorrect timing can cause increased fuel consumption.
• Engine misfire: Occasional or persistent misfires, sometimes with additional misfire codes.
• Stalling: Engine may stall when coming to a stop or at idle if the signal cuts out.
• Variable valve timing issues: VVT systems may default to a failsafe mode, reducing performance.

Common Causes of P0398

Most Common Causes

• Failed camshaft position sensor “B” (Bank 2): Internal sensor failure is very common, especially on high-mileage engines or where the sensor is exposed to heat and oil.
• Damaged wiring harness: Chafed, pinched, or broken wires between the cam sensor and ECU can cause intermittent or high-voltage readings.
• Corroded or loose connector: Oil intrusion, moisture, and road salt can corrode terminals, causing poor contact and noisy signals.
• Incorrect sensor installation: After previous repairs, a sensor not seated fully, wrong part number, or incorrect air gap can trigger P0398.
• Low-quality aftermarket sensor: Cheap sensors sometimes produce unstable signals that the ECU flags as out of range.

Less Common Causes

• Timing chain or belt issues: Excessive slack, a jumped tooth, or worn guides can cause the camshaft position to disagree with the crankshaft signal.
• Failed reluctor ring / tone wheel: Cracked, bent, or misaligned tone wheel on the camshaft can distort the signal.
• Internal engine wear: Severe camshaft or bearing wear can cause erratic positioning that shows up as an electrical fault.
• ECU / PCM fault: Rare, but an internal driver or processing issue in the engine computer can misread a good sensor.
• Ground or power supply problems: Poor engine grounds or low reference voltage affecting multiple sensors.

Diagnosis: Step-by-Step Guide

You’ll want a basic OBD-II scan tool (preferably one that can read live data and Mode $06), a digital multimeter, and ideally an oscilloscope for viewing sensor waveforms. A wiring diagram for your specific vehicle and access to service information are also very helpful.

1. Confirm the code: Use a scan tool to verify P0398 is present. Note any related codes (like other cam/crank or VVT codes) that may point to a bigger timing issue.
2. Check freeze frame data: Look at engine RPM, load, and temperature when the code set. This helps you reproduce the conditions that caused the fault.
3. Visual inspection: Locate camshaft position sensor “B” on Bank 2. Inspect the sensor, wiring, and connector for oil contamination, broken insulation, rubbing on brackets, or loose plugs.
4. Wiggle test: With the engine idling, gently move the harness and connector while watching live data for the cam sensor or for the engine to stumble. If the signal drops or the engine reacts, you likely have a wiring or connector issue.
5. Check power and ground: Using a multimeter, verify that the sensor has proper 5V reference (or 12V, depending on design) and a good ground. Any missing or low voltage needs to be traced back to the source.
6. Signal voltage test: Back-probe the signal wire and monitor voltage while the engine is running. You should see a steady switching pattern (often between about 0.5–4.5V). Spikes, dropouts, or a flat line indicate a problem.
7. Compare with other bank / sensor: If possible, compare Bank 2 sensor B data with Bank 1 or sensor A. Large differences in pattern or timing can confirm a fault on Bank 2.
8. Scope test (advanced): With an oscilloscope, view the cam sensor waveform and compare it to the crankshaft sensor signal. Irregular spacing or missing teeth may point to a tone wheel or timing issue rather than just the sensor.
9. Inspect mechanical timing: If electrical tests look good but the code persists, remove necessary covers and check timing marks, chain/belt condition, and tensioners.
10. Clear codes and road test: After repairs, clear P0398 and perform a road test under similar conditions to the freeze frame data. Re-scan to confirm the code does not return.

Pro tip: Before condemning the ECU, temporarily swap cam sensors between banks (if they are identical and accessible). If the fault follows the sensor to the other bank, you’ve confirmed a bad sensor rather than a wiring or ECU issue.

Possible Fixes & Repair Costs

Repairs for P0398 range from simple sensor replacement to more involved timing work. A typical camshaft position sensor “B” replacement on Bank 2 usually costs around $120–$350 parts and labor at most independent shops, depending on access and vehicle type. Wiring repairs can run $100–$300 if harness sections need to be spliced or replaced. If timing chain or belt issues are found, expect $600–$1,500 or more. ECU replacement or reprogramming, while rare, can push costs above $800. Labor rates, vehicle design, and parts quality all affect the final price.

Can I Still Drive With P0398?

In many cases, you can still drive with P0398 for a short period, but it’s not ideal. If the engine runs reasonably well and the only symptom is a check engine light, you may be able to drive to a shop or finish a short trip. However, if you notice severe rough running, stalling, or hard starting, you risk being stranded or causing additional damage. The ECU may switch to a backup strategy that reduces power and fuel economy, and prolonged driving with incorrect timing can stress the catalytic converters and other components.

What Happens If You Ignore P0398?

Ignoring P0398 can turn a relatively simple electrical repair into a more expensive mechanical problem. Erratic cam timing can lead to long-term misfires, raw fuel entering the exhaust, and overheated catalytic converters. If the underlying issue is a worn timing chain or tensioner, continued driving can eventually cause serious internal engine damage. Addressing the code early usually saves money and prevents inconvenient breakdowns.

Last updated: March 1, 2026

Vehicles Commonly Affected by P0398

P0398 shows up most often on multi-bank engines with dual cam sensors, such as V6 and V8 setups. In the field, I see it frequently on:

• GM / Chevrolet / GMC: V6 and V8 trucks and SUVs with variable valve timing.
• Ford / Lincoln: Modular V8 and some V6 engines with separate intake and exhaust cam sensors.
• Chrysler / Dodge / Jeep / RAM: Pentastar V6 and HEMI V8 engines.
• Toyota / Lexus: V6 and V8 models using multiple cam sensors per bank.
• Nissan / Infiniti: VQ-series V6 and VK-series V8 engines.

That said, any OBD-II vehicle with a dual-bank, dual-cam sensor setup can set P0398 if the Bank 2 sensor B signal becomes unstable.