Maybe overthinking this. I was recently battling some misfires, lean/rich, and assorted other issues which included this code. Believe I've solved the misfires but this code still keep showing up along with the P1461, which is low signal to cat bank 1 (a mystery code for most). If BMW is like most other makes, the knock sensor code will not on it's own trigger the CES light but when another code does, in this case 1461, it's there lurking in the background and many think the codes go together which is not the case. The P039 can be sitting there and you'd never know until a new code triggered the light and you took a read.
My question is this. Is it more likely the P039 telling me there is a knock being sensed, or that the knock sensor has gone bad?
P-codes are always P and then 4 numbers.
There is no valid code P0039 or P0390 that I could find for any E38 ECU.
What code reader are you using, and what code are you actually getting? Does it start with a P on the reader?
BMW also has their own fault codes, which depending on reader can be displayed in decimal or hex.
For the M73 DME, code "39" would be "EWS 3.3 tampering protection" , which only shows up in one of the two documents I have for codes. Hex code "0x39" (57 decimal) would be misfire on cylinder 8, the same as P0308.
In general, knock sensor codes indicate a problem with the knock sensor (in my experience it's always been damaged wiring).
I should just wipe this post out and start over lol.
i meant knock sensor, and the code is P0325
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