I’ve got a ‘99 E350 with a P0325 - Knock Sensor code. I have not noticed any knocking or poor performance issues with the vehicle. I have reset the code several times and it keeps reoccurring. I suspect that the knock sensor is bad or that its wiring has been compromised. But, as the sensor is so conveniently located, I’d like to confirm a faulty unit before removing the intake to replace it. Is there any easy way to test the sensor without removing it first? The only info I’ve found online involves a scope. Alternatively, I’m thinking about buying a replacement sensor and plugging it in without installing it on the engine. I’m thinking that if I were to drive with a new one plugged in but not mounted for a while without a reoccurrence of the code, that would essentially confirm a bad sensor. If the engine were performing poorly, I’d be hesitant to do this, but as it seems to be running fine, I’m thinking it would be okay...no different than driving it with a bad sensor, right? I’m assuming that the ECU only adjusts timing based upon input from the knock sensor when the knock sensor detects pre-detonation? Does anyone have any knowledge or thoughts on this? TIA.

 

Well, I guess no one here knows much about knock sensors (KS). I was able to find a few threads on here, but like mine, very few responses. So, if anyone stumbles upon this thread here’s what I found with mine, for what it’s worth. I went and pulled the KS off of a parts donor van that I have. The intake had already been pulled, so that was no big deal and gave me a good idea of where the thing is located in case I decided to try the remove the alternator approach to get to it. Since no one could tell me how to test it and/or if running the vehicle with an unmounted KS was a good idea or not, I decided to give it a try. I figured that it couldn’t be any worse than running it with a bad KS. I pulled the doghouse and when I went to unplug the bad KS, I found that the wire harness, right behind the KS side of the plug was damaged. It looked almost like it had been cut, but not all the way through. I’m not quite sure how that might have happened. I had expected to find the wiring harness damaged at some point, but I was more expecting that a mouse had chewed it down in the engine valley. I sure didn’t expect to find damage in an accessible location. I got lucky. I pulled the plug apart and was able to solder the three wires, apply heat shrink and reassemble the plug. All fixed and (so far, knock on wood) no more CEL.

So so for anyone reading this any having a similar problem, I think it is safe to say that running you vehicle with an uninstalled KS for a while in order to verify a bad KS before removing the intake to replace it would be fine, assuming that you aren’t having other issues that are causing poor performance that might necessitate your KS being more “actively involved”. I was driving mine for quite some time with the wires cut (two of three were completely severed and the third was mostly severed) and I noticed no significant performance issues. I will certainly try a new KS plugged in but not installed to see if it cured the CEL before pulling the intake and replacing it, if I have a similar issue in the future.

Good luck!

 

This is good info for what seems to be an issue not many have dealt with their own selves. It is odd the wire harness could be affected as you describe considering where its located. Could that be due varmints chewing through it?

 

It was a pretty clean cut. I didn’t test to see if it was possible, but my best guess is that it got clipped by the edge of the doghouse as it was being reinstalled at some point. That’s the only thing that makes any sense to me.