P1333
Knock Sensor 4 High Input.
- BMW
- Powertrain
- Manufacturer code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 1
- Defined byThe manufacturer
- 3
- AreaIgnition system or misfire
- 33
- FaultThe specific fault in that area
What it means
P1333 is a BMW-specific code for Knock Sensor 4 High Input. The engine control unit saw the signal voltage from the fourth knock sensor circuit stay above its expected range. This usually points to a wiring fault, a poor connection or a failed sensor. Which cylinders knock sensor 4 covers depends on the engine, so check model-specific data.
Symptoms
- Engine warning light on
- Reduced power or flat response under load
- Slightly worse fuel economy
- Rough or hesitant running in some conditions
- Possible pinking or knocking noise under load if the engine is no longer protected
Possible causes
- Faulty knock sensor 4likely
- Damaged, chafed or oil-soaked wiring to the sensor, causing a short to voltage or a high signallikely
- Corroded, loose or contaminated connector at the sensor or control unitpossible
- Incorrect sensor mounting torque or poor contact with the engine blockpossible
- Coolant or oil leak contaminating the sensor or harnesspossible
- Fault inside the engine control unit's knock sensing circuitrare
How to diagnose
- Read all stored codes and freeze frame data, and note whether other knock sensor codes are also present.
- Check the engine for obvious mechanical noise or a leak near the sensor before assuming an electrical fault.
- Inspect the sensor wiring and connector for chafing, heat damage, oil or coolant contamination and corrosion, following the harness route for your engine.
- Confirm the sensor is the correct part for that position and is fitted and tightened to the manufacturer's torque.
- Check the sensor circuit for a short to voltage, an open circuit or high resistance, using the wiring diagram and test values for your model.
- Check the sensor's resistance or signal against manufacturer data, with the connector unplugged where specified.
- Inspect the control unit connector pins for spread, corrosion or moisture.
- Clear the code and road test, watching live knock sensor and ignition retard data to confirm the fault does not return.
How to fix
- Repair or replace damaged wiring and terminals in the knock sensor 4 circuit.
- Clean or replace a corroded or contaminated connector.
- Replace knock sensor 4 with the correct part and tighten it to the specified torque.
- Fix any oil or coolant leak that is soaking the sensor or harness, then replace any affected parts.
- Only after all else is ruled out, have the control unit tested and repaired or replaced as the manufacturer advises.
Can I keep driving?
Medium severity
The car can usually be driven for a short time, but the engine may run with reduced timing and power, and knock protection could be compromised. Get it diagnosed soon and avoid heavy loads or hard acceleration until it is fixed.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.