Faulty knock sensor 4 (open or shorted internally, or damaged by heat/age); Damaged or corroded wiring harness and connector at the knock sensor; Poor electrical connection at the DME connector for the knock sensor circuit; Knock sensor installed with incorrect torque or loose mounting, altering its signal; Engine mechanical noise (e.g., loose internal components) mimicking a high knock signal; Water or oil contamination in the knock sensor connector causing high resistance; Failed DME internal circuit for the knock sensor input (rare)

DTC codes / BMW codes / P1333

P1333 · BMWKnock Sensor 4 High Input

Q: What does code P1333 mean?

Knock Sensor 4 High Input. P1333 on a BMW means the engine control module (DME) has detected an abnormally high voltage signal from the knock sensor assigned to cylinder 4, indicating a fault in that sensor's circuit or the sensor itself. The DME monitors the knock sensor's return voltage to detect engine knock, and a high input tells the module the signal is outside its expected range, so it may retard ignition timing as a protective measure.

P1333 on a BMW means the engine control module (DME) has detected an abnormally high voltage signal from the knock sensor assigned to cylinder 4, indicating a fault in that sensor's circuit or the sensor itself. The DME monitors the knock sensor's return voltage to detect engine knock, and a high input tells the module the signal is outside its expected range, so it may retard ignition timing as a protective measure.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Reduced engine performance or sluggish acceleration because the DME may default to a safe ignition timing map
Poor fuel economy as the engine runs with retarded timing
Occasional engine misfire or rough running under load if the fault affects knock detection
In rare cases, a slight knocking or pinging sound if the DME cannot properly detect and correct knock

Common causes, most likely first

Faulty knock sensor 4 (open or shorted internally, or damaged by heat/age)
Damaged or corroded wiring harness and connector at the knock sensor
Poor electrical connection at the DME connector for the knock sensor circuit
Knock sensor installed with incorrect torque or loose mounting, altering its signal
Engine mechanical noise (e.g., loose internal components) mimicking a high knock signal
Water or oil contamination in the knock sensor connector causing high resistance
Failed DME internal circuit for the knock sensor input (rare)

How to diagnose and fix it

Scan all modules for stored codes and freeze-frame data to confirm P1333 is current and not a ghost code
Visually inspect the knock sensor 4 and its wiring for damage, corrosion, or loose connection
Check the sensor's mounting bolt torque and ensure the mating surface is clean and free of debris
Measure resistance and voltage on the knock sensor circuit according to BMW service information
Swap the knock sensor with a known-good one from another cylinder to see if the code follows the sensor
Repair or replace damaged wiring or connector pins as needed
Clear codes and perform a road test to verify the repair, replacing the sensor if the code returns

Knock sensor 4 high input: what techs overlook

A high input code often results from a poor ground or loose sensor mounting rather than a failed sensor, so always check torque and cleanliness before replacement.
The DME may set P1333 due to interference from other engine noises, such as a failing timing chain tensioner, which can be misdiagnosed as a sensor fault.
On some BMW engines, the knock sensor for cylinder 4 is located under the intake manifold, making it labor-intensive to access, so confirm the fault before committing to replacement.
After replacing a knock sensor, the DME adaptation values may need to be reset with a capable scan tool to prevent the code from reappearing immediately.
P1333 can be stored intermittently due to a chafed wire that only shorts when the engine moves under load, so wiggle-test the harness while monitoring live data.

Can I keep driving with P1333?

You can usually continue driving with P1333, but avoid heavy acceleration or towing until the fault is repaired, as the engine may be running with reduced timing advance and performance. Prolonged driving with a knock sensor fault can lead to increased emissions and potential engine damage if knock goes undetected.

Tools that help

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Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.