knock sensor ohms

Is there any way to test the resistance on a knock sensor? I want to make sure they are faulty before I replace.

Are they giving you any codes, if not they should be good.
They are piezoelectric devices, not sure you can get an ohm reading from them.

Originally Posted by JimLev

Are they giving you any codes, if not they should be good.
They are piezoelectric devices, not sure you can get an ohm reading from them.

Correct but they need to be torqued very specifically. Sometimes you can retorque them and theyll work fine. I like to remove and clean the mounting area, then retorque. Never done an E39 but its worked on other cars...

Dunno if it adds any value, but I typed /knock sensor F3 in the bestlinks and this came up which may be of some help:
- How to better understand the piezoelectric knock sensor operation (1)

Originally Posted by Flug540

I finished rebuilding my sensors over the weekend. Wasn't too bad, the first one took the longest time while I was trying to figure out the best technique. Below are some photos of the process and what they look like now. On the first two photos you can see what happens to the original internal insulation when you pull the outer shell. Resistance on all sensors actually gone up slightly, now it's about 4.98 MOhm, which I think shows that the original insulation already was beginning to conduct.

Originally Posted by bluebee

Dunno if it adds any value, but I typed /knock sensor F3 in the bestlinks and this came up which may be of some help:

Cool post. I've never seen that bad insulation deterioration that's for sure! Interesting that the Bosch knock sensors look exactly the same as every other European car I've ever seen one on... I wonder if they are all identical just with different end connectors.

Originally Posted by geargrinder

I wonder if they are all identical just with different end connectors.

I wonder also.

What would be nice, if someone gets a chance, is to snap a photo of the knock sensors in situ, on the engine, so that I can post it to this engine thread:
- Getting to know your M54 engine, a photo & identification guide to every visible part in the engine bay (1)