What does code P0325 mean on a Mercedes-Benz and is it safe to drive?
P0325: Knock Sensor 1 Circuit Malfunction (Bank 1). Here's what it means on your Mercedes-Benz, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
What this code means
The PCM isn't receiving a valid signal from knock sensor 1. Without knock feedback, the PCM retards ignition timing as a safety measure, reducing power and economy.
Common causes for your Mercedes-Benz
- Failed knock sensor
- Corroded or broken wiring/connector at the sensor
- Actual engine knock from carbon buildup or low-octane fuel
Symptoms
- Check Engine Light
- Reduced power and fuel economy (PCM retards timing)
- Possible audible knock or ping under load
Typical fixes
- Replace knock sensor
- Repair wiring and connector
- Use correct octane fuel and address carbon buildup
Repair cost range
For a Mercedes-Benz, repairs for P0325 often fall between $150 and $500, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Mercedes-Benz
Mercedes P0325 on M272 3.5L V6 is important in context of the balance shaft gear failure—a worn balance shaft causes mechanical vibration that the knock sensor may misinterpret, or conversely, sensor damage from severe vibration can set P0325. On M274 2.0T turbocharged engines, the knock sensor harness routes near the turbo exhaust housing; heat damage to the insulation is a common P0325 cause. On AMG-variant engines using higher compression ratios, a non-functional knock sensor is a serious protection issue; do not drive extended distances with active P0325.
Most commonly affected models