Actually it's 7 red/white wires connected together: (like shown on the diagram I linked on my previous post)
*1x 1,5 mm2 supply from fuse F4
*4x 0,5 mm2 lambda heating
*2x 1,5 mm2 EGS

https://bmwteka.com/wds/en/e53/57056cbb

I think this is the guy who did his own head gasket so the harness is probably pinched or damaged behind the cylinder head/valve cover. Might be wise to check for something obvious before getting into the Ebox and cutting wires.

Under my car were splices that were melted. PO did a great hack job. Harness just laying on the exhaust.

Doesn't hurt to make sure it's good under there.

:iagree:

This, because I almost pinched those harnesses under my valve cover on my e46 doing the m56 valve cover mod. Very easy to screw up that way if not paying attention.

Yes makes sense to see if that main harness got pinched. The "cutting wires" is 2/10 difficulty since they are already terminated in a crimp terminal. If you cut of the terminal careful with a Dremel or sharp small diagonal cutter you won't even have to strip any wires to reassemble.


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Thanks all. I was thinking about pulling the valve cover today, and may still but I don’t suspect that’s the problem. Oddly, all of the O2 wires appear sound and rubber insulator still good. One of the downstream ones has a good bit of the rubber insulator torn so I stripped a good bit of it off expecting an obvious break or shorted spot. Found none.

I connected my Multimeter with the red probe in the hot side of the fuse 4 slot and the O2 harness and got 12v on pins 1 and 3 and something like 7.5v on pins 2 and 4 with key in pod 2. Both banks. ( pins have no real reference point but it simply was every other one was 12v)

Not sure this proves or disproves anything but it was my understanding that only one of the 4 O2 wires (red/ws heater) received voltage.

Of course it started raining and the car is outside….


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Mention of a 6-wire connector or possible a 7 wire from the wiring diagram. Possible this is all on one bus (connector) that can be unplugged to test for continuity?


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No need to remove the valve cover unless it's pinched on the harness.

You should check the harness from the back of engine over to the eBox

An endoscope or inspection camera comes in handy for these sort of tasks.

Yes, it does. I have one.... can't believe I forgot i did. I buried it away after I used it last year.

Fairly inexpensive on Amazon. Used one on my n54 when it shredded a belt. Those are notorious for pulling the belt into the oil pan through the crank.

Came in handy to look inside my oil pan.

Definitely will be handy to look in the tight spaces where Those harnesses run.