Failed knock sensor 4 due to internal damage, heat exposure, or contamination; Damaged or corroded electrical connector at the knock sensor; Open or shorted wiring in the knock sensor 4 circuit, often from chafing or rodent damage; Loose or improperly torqued knock sensor mounting bolt, altering the sensor's ability to detect vibrations; Engine mechanical noise (such as a failing timing chain tensioner or valve train tick) mimicking knock and confusing the sensor; Faulty engine control module (ECM) knock sensor input circuit, though this is rare

DTC codes / BMW codes / P1385

P1385 · BMWKnock Sensor 4 Circuit

Q: What does code P1385 mean?

Knock Sensor 4 Circuit. P1385 on a BMW indicates that the engine control module has detected an abnormal signal from the knock sensor assigned to cylinder bank 4, which is typically the sensor monitoring the rear-most cylinders on V12 or high-cylinder-count engines. The circuit voltage or resistance falls outside the expected range, preventing the computer from reliably detecting detonation and adjusting ignition timing to protect the engine.

P1385 on a BMW indicates that the engine control module has detected an abnormal signal from the knock sensor assigned to cylinder bank 4, which is typically the sensor monitoring the rear-most cylinders on V12 or high-cylinder-count engines. The circuit voltage or resistance falls outside the expected range, preventing the computer from reliably detecting detonation and adjusting ignition timing to protect the engine.

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 due to the computer defaulting to a conservative ignition timing map
Audible engine knock or pinging under load if the fault allows timing to advance without proper knock detection
Rough running or misfire-like behavior in severe cases where the faulty sensor signal disrupts timing control
Poor fuel economy as the engine management system retards timing to a safe baseline

Common causes, most likely first

Failed knock sensor 4 due to internal damage, heat exposure, or contamination
Damaged or corroded electrical connector at the knock sensor
Open or shorted wiring in the knock sensor 4 circuit, often from chafing or rodent damage
Loose or improperly torqued knock sensor mounting bolt, altering the sensor's ability to detect vibrations
Engine mechanical noise (such as a failing timing chain tensioner or valve train tick) mimicking knock and confusing the sensor
Faulty engine control module (ECM) knock sensor input circuit, though this is rare

How to diagnose and fix it

Perform a visual inspection of the knock sensor 4 and its wiring for obvious damage, corrosion, or loose connections
Check the sensor's mounting bolt torque and ensure the mating surface is clean and free of debris
Measure the resistance of the knock sensor with a multimeter and compare to BMW specifications for your engine
Back-probe the sensor connector and check for the presence of the reference voltage or bias signal from the ECM
Inspect the wiring harness between the sensor and ECM for continuity, shorts to ground, and shorts to voltage
If the sensor fails electrical tests, replace it with a quality OEM-equivalent part and clear the fault memory
After repairs, verify the code does not return during a test drive that includes acceleration under load

Knock sensor 4 faults that fool technicians

A loose knock sensor bolt is a common cause of P1385 that many technicians overlook because the sensor itself tests fine on the bench, but the improper torque prevents it from picking up vibrations correctly.
On BMW V12 engines, knock sensor 4 is often located in a difficult-to-reach area, and a faulty sensor can sometimes be caused by oil or coolant contamination from a leaking gasket above it.
The code does not always mean the sensor is dead; a poor ground connection at the engine block can skew the sensor signal and set the same fault.
Mechanical noises from a failing accessory drive belt tensioner or a loose heat shield can be misinterpreted by the knock sensor as detonation, leading to a false P1385.
Replacing the sensor without checking the connector pins for tension loss or corrosion often results in the code returning within a few hundred miles.

Can I keep driving with P1385?

You can generally continue driving with P1385, but avoid heavy acceleration or towing until the fault is repaired, as the engine may be running with reduced timing advance and could be susceptible to knock damage under load. If you hear audible pinging or experience significant power loss, have the vehicle checked promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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