P0333
Knock/Combustion Vibration Sensor B Circuit High.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 3
- AreaIgnition system or misfire
- 33
- FaultThe specific fault in that area
What it means
P0333 is the generic code for a high signal in the circuit of knock or combustion vibration sensor B, which is usually the sensor on the second bank of the engine. The engine control unit has seen the sensor signal voltage or activity sitting above the expected range, or has detected a fault in the circuit. As the knock signal can no longer be trusted, the control unit normally retards the ignition timing as a precaution.
Symptoms
- Malfunction indicator lamp on
- Reduced power and flat acceleration
- Poorer fuel economy
- Pinking or rattle under load if knock is not being detected
- Rough running or hesitation under load
- Engine running in a protective limp mode on some models
Possible causes
- Faulty knock sensor B (internal fault or sensor failure)likely
- Damaged, chafed or corroded wiring to the sensor, including a short to voltage or a signal wire shorted to a power supplylikely
- Poor connection at the sensor or control unit connector, such as corrosion, bent pins or water ingresslikely
- Sensor loose or incorrectly torqued, or mounting surface contaminated, giving a false signalpossible
- Mechanical engine noise being picked up, such as worn bearings, piston slap or loose components near the sensorpossible
- Fault inside the engine control unitrare
- Outdated control unit software where a known fault exists for that enginerare
How to diagnose
- Read all stored and pending codes and the freeze frame data to see engine load, speed and temperature when the fault set, and check for other knock or misfire codes.
- Check which physical sensor is sensor B for this engine, as the location and bank numbering depend on the model and engine layout.
- Visually inspect the sensor wiring and connector for chafing, heat damage, oil contamination, corrosion and water ingress.
- Check the sensor is fitted correctly and the mounting bolt is tightened to the manufacturer's torque, as it is sensitive to this.
- With the ignition on, check the reference and signal circuit voltages against the manufacturer's data, and check the signal and wiring for shorts to voltage and for continuity.
- Measure the sensor resistance or output where the manufacturer gives a specification, and compare against the other bank's sensor if fitted.
- Watch live data for knock activity or retard at idle and when the engine is warm, and listen for any genuine mechanical noise.
- Check for any manufacturer service bulletins or software updates for the engine, if all the above checks are fine.
How to fix
- Repair or replace damaged wiring and clean or replace corroded connectors.
- Replace the knock sensor B if it is out of specification, using the correct type and tightening to the specified torque.
- Clean the mounting face and refit the sensor correctly if it was loose or contaminated.
- Repair any underlying mechanical fault causing excess noise, once confirmed.
- Update the control unit software only if a manufacturer bulletin lists this as a known cause for the engine.
- Replace or repair the control unit only after wiring and sensor have been proven good.
Can I keep driving?
The car can usually be driven for a short time, but the timing will be retarded and the engine may not protect itself from real knock. Avoid heavy load and book the repair soon to prevent possible engine damage and poor economy.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.