P0331Knock/Combustion Vibration Sensor B Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- The knock sensor is a piezoelectric structure-borne sound sensor bolted to the engine block; the module evaluates its signal per cylinder and retards ignition when it detects knock. Sensor B is the second sensor – bank 2 on V engines, but on some four-cylinders also bank 1. With a fault the module retards ignition across the board as protection – noticeable loss of power and higher consumption. P0331 means the circuit is electrically sound but the signal is implausible. GM sets it when the filtered background noise stays below a threshold – typically a loose sensor or one not bolted down properly – in the first trip; Saab's GM-based engines also when excessive knock persists on several cylinders or a whole bank for 8–10 s. Ford does not use this code.
- What you may notice
- Check engine light on
- Loss of power, sluggish response from ignition retard
- Higher fuel consumption
- Likely causes
- LikelySensor loose, wrongly torqued or mounted with sealant or on a dirty surface
- PossibleEngine software or calibration (bulletins for some models)
- PossibleGenuine knock on a whole bank or mechanical noise
- RareSensor aged or damaged (low sensitivity)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €0 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.