P0325 on a Mercedes-Benz: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

You can drive, but the engine runs with reduced timing protection and fuel economy may drop, so have the knock sensor checked soon.

What P0325 means on a Mercedes-Benz

On a Mercedes-Benz, P0325 means the knock sensor on bank 1 is not sending a proper signal to the engine computer. The sensor detects engine knock so the computer can adjust ignition timing; a bad sensor circuit leaves the engine without that protection.

Is P0325 common on Mercedes-Benzs?

P0325 appears on Mercedes V6 and V8 models, especially C-Class, E-Class, GLC, and ML. Knock sensor failure and wiring or connector issues near the sensor are the usual causes, and on many engines the sensor is buried under the intake manifold.

Commonly reported on: C-Class, E-Class, GLC, ML.

Symptoms

Check engine light on
Reduced fuel economy
Engine pinging under load
Slight loss of power

Common causes

most common: Failed knock sensor
common: Chafed or damaged sensor wiring harness
common: Corroded or loose sensor connector
rare: Engine computer issue

How to fix it

Fix	DIY?	Typical cost
Replace the knock sensor	Mechanic	$300–700
Repair the wiring harness near the sensor	Mechanic	$150–400
Clean and reseat the sensor connector	Yes	$20–80

Frequently asked questions

Can I drive a Mercedes-Benz with a P0325 code?

Yes, in most cases. The engine still runs, but without knock protection it may ping under load, and fuel economy can drop, so get it checked soon.

What usually causes P0325 on a Mercedes-Benz?

A failed knock sensor or wiring damage near the sensor, which is common on Mercedes V6 and V8 engines. On many models the sensor sits under the intake manifold.

How much does it cost to fix P0325 on a Mercedes-Benz?

Replacing the knock sensor typically runs $300–700 with parts and labor because access is tight. A wiring repair is usually $150–400.