E36 M3 Knock Sensor Replacement DIY, Not So Easy

Date: 05/03/11
Mileage: 147,000

So after I initially broke down my car was throwing the code 1226. Which is "Failed Knock Sensor #2." Instead of realizing this code was just stored in the computer for about a year now, I took it as the cause of my no-start situation. I ordered 2 knock sensors from RMEuropean for about $65 a piece. I figured I would do both while I'm in there.

I had read on BFC that you can do #2 (the rear most KS) without removing the intake manifold. Honestly this is bullshit and you have to remove it. Unless you have removed every single other thing down there already, broken factory clips and don't care about torquing things down correcting, and have tiny monkey hands, (my hands are already not big), then maybe you could do it. But honestly it just takes another 20 minutes to pull the intake manifold off. Just do it, it sucks, but makes life a lot easier.

So this is what I was dealing with. Car got dropped off in the street by the tow truck. At least it was under a tree!

So the first sensor is pretty easy. All you need to do is really remove the alternator ducting tube and intake.

It's just behind the ICV. This extension basically shows the location of the first knock sensor. You don't have to do much, you can easily use a torque wrench at this point.

I pulled the first sensor out and it looked fine. Of course my problem was the KS#2 but I thought I would replace it anyway. It looks like someone already did the easy one. Oh well, I sold it for $40.

Next up is the bitch sensor. Like I said there is no real way to get the bracket off that protects the sensor without removing the intake manifold. Next step, remove the intake manifold. To do this, remove the fuel lines from the fuel rail and every other thing that is attached to the manifold. The front 6 nuts are easy to loosen, the rear most nut is the bitch. I had to get in there with a 11mm open end wrench and get my hand under the manifold and remove it slowly. Not sure how else you can get that nut off.

To remove the entire manifold I also loosed the wiring harness cover that is under the cowl. This helped as I ripped it out and placed it out of the way.

Gratuitous shot of my baller chrome pink top injectors.

While you're down there, it would be a good time to clean the ICV if you haven't done that already. Ok, so here is the shot of the bracket that is covering the rear knock sensor.

With the manifold removed it's easy enough to remove this bracket. I think it is 2 13mm bolts. Underneath the bracket you can see the cracked up knock sensor that has been throwing faults.

Remove this guy and remember which plug it's plugged into. Last thing you want to do is plug it into the CPS or something. It can be easy to confuse when you're removing things so label your harness or be conscious of it.

So here's some shots of what were working with.

Obvious why it wasn't working. Here's a shot of the old one and new one side by side.

Funny thing is that the knock sensor #1 looked just like this new one here. There was little wear on it. This leads me to believe that KS#1 was changed with the last 20k miles or so. Makes sense because it's easy to change out. Not the same for #2. That looks about as old as the car itself.

When reinstalling everything the torque value on the knock sensors themselves is very low. Like 12ft-lbs or something. They just barely tighten to the block. If you haven't put in new intake manifold gaskets in a while, like never, I would do that too.

Impressions are that the car pulls a little more solid now. Before there would be a flat spot in the beginning but now that is all smoothed out. I recommend doing this if you are throwing the code.