N55 Knock sensor shows 19 volts
Hi guys,
Car in question is a BMW F10 535i (225 kW).
I’m chasing an issue with the knock sensor and some irregular misfires. The misfire usually shows up on cylinders 1 and 3, and for some reason the knock sensor is reading 19 volts. The voltage goes back to normal once the engine warms up, but there are still no error codes at all.
To rule things out, I swapped parts from cyl 1 to cyl 2:
- coils
- spark plugs
- injectors
Compression was also tested and everything looks normal.
The car has no catalytic converter, and when I unplug the O2 sensor, the misfire suddenly shifts from 1 and 3 to 4 and 5. Still doesn’t explain why the knock sensor is showing 19 volts. Could it be the ECU? A bad knock sensor? Wiring shorting somewhere? Not sure where it would even get that much voltage.
No error codes for anything, and the car drives fine. The issue is only noticeable at idle.
Any kind of information is appreciated!
Thanks in advance!
Posted Dec 7, 2025, 11:52 PM UTC