knock sensor on 540i -- how robust?

Hi all:

How reliable are the knock sensors on the BMW 540i?
At 100K miles, should they be changed?

On my previous car (a nissan), the knock sensors were known to be flaky and/or over-sensitive with age, and yet show no fault codes.

How easy is it to access the knock sensor on a 540i?

I've not heard of anyone replacing them. I'm sure they would throw a CEL if failed or failing since they are an integral part of the motor control system.

I believe they are located in the valley, one against each bank of cylinders. That means the intake manifold and the valley pan would have to come off.

Yeah, the knock sensor in my Nissan was also in the valley.

But how would the engine computer actually know that the knock sensor was bad?

When a car really is pinging, will that cause erratic o2 sensor readings? If so, then that would be how the computer could cross reference the knock sensor vs. the O2 to see if the knock sensor was really bad.

But its my understanding that knocking or pinging is the spontaneous ignition of all the fuel, so maybe the O2 sensor wouldn't indicate very rich or very lean in either direction with such a condition. So if that were true, then how would the engine computer have any way of knowing the knock sensor was bad?

Looking at the manual for my Peake code reader, there are fault codes for bad knock sensors - right down to which one of the four is bad.

Originally Posted by Fulltone74

Yeah, the knock sensor in my Nissan was also in the valley.

But how would the engine computer actually know that the knock sensor was bad?

When a car really is pinging, will that cause erratic o2 sensor readings? If so, then that would be how the computer could cross reference the knock sensor vs. the O2 to see if the knock sensor was really bad.

But its my understanding that knocking or pinging is the spontaneous ignition of all the fuel, so maybe the O2 sensor wouldn't indicate very rich or very lean in either direction with such a condition. So if that were true, then how would the engine computer have any way of knowing the knock sensor was bad?

Pre-ignition and detonation are different but both would cause a knock. In both cases all the fuel/air mixture is burned but not instantaneously. The oxygen sensor would not be able to detect the condition.

Many systems on the car are self diagnosing by sending a test signal to the unit. So even if your car was not knocking but your knock sensor went out the system would detect it and send a CEL.