What it means
Knock sensor B signal is in electrical range but plausibility check fails — typically a loose mounting, wrong torque, or sensor element drift.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Knock sensor B monitors engine vibration, and the controller checks whether its signal is plausible for engine speed and operating conditions. P0331 means the signal is present but its behavior falls outside the expected range or performance pattern; a loose sensor or a deteriorating sensor can distort what the controller detects.
Common causes
Most likely first.
- Sensor loose
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Check-engine light
- Reduced engine power or acceleration
- Engine knocking may be more noticeable
How to diagnose it
- Review freeze-frame and live knock-sensor data, along with related codes, to see whether the implausible reading occurs at particular engine speeds or loads.
- Identify sensor B using the vehicle wiring information, then inspect its mounting and connector for looseness, corrosion, or damaged wiring.
- If the sensor has been disturbed, verify its mounting and tightening procedure against the manufacturer's specification; incorrect mounting can affect vibration detection.
- Check the sensor circuit and signal using the manufacturer's diagnostic procedure to distinguish a sensor fault from a wiring problem.
- Investigate network or module faults only if vehicle service information identifies sensor B data as network-routed and the sensor circuit checks out.
Common fixes
- Secure sensor B and mount it according to the manufacturer's procedure.
- Repair damaged wiring or a loose or corroded sensor connector.
- Replace sensor B if it fails the specified signal or performance test.
- Address a confirmed control-module or network fault only after circuit and sensor checks.
Can I keep driving?
Use light throttle and avoid heavy acceleration while the controller's knock response may be unreliable. If knocking becomes pronounced or power drops sharply, stop driving and have the cause checked.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.