Dreaded trans. Failsafe prog.
 

The pre-cats are right in front of me but can’t seem to locate the downstream connectors. Are you saying they are likely in keepers on the rear behind the intake or valve cover?


Ok, I just figured out they are under the vanity cover. Duh.


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They are clipped on top between the valve cover and the intake manifold. Under the beauty panel.

https://www.pelicanparts.com/BMW/tec...mall/pic07.jpg

Thanks, beat me too it…..


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Minor update: looks as if someone changed the downstream O2 (or at least one) as one of the connectors was missing from under the vanity cover. Just laying on the back of the engine . Cable heat tube was heavily frayed either from heat or critter chewing but so far no sign of short or damaged wire.

Ran out of time, back at it tomorrow.


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Unplug the damaged wire and see if they fuse doesn’t blow

Well, I tried the unplug thing. No joy. I have now unplugged all 4 O2’s individually resulting in 4 dead fuses……

I’m going to have to test for continuity at the connectors and hope that the short is somewhere accessible.

I suppose it’s possible the TCM module has the short? Any advice on testing that that can be done with a multimeter.

For clarity, the fuse blows in Key Pos 2 not started.
Once started the data stream shows both down stream O2’s getting voltage, neither upstream. Odd, since the fuse connects to all 4.


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Plug all 4 o2's back in and unplug the TCM and see if the fuse blows in pos 2?

The o2 sensors "produce" a signal voltage they don't "get" voltage. The voltage supplies only the o2 heaters to get them "producing" a voltage faster as they need to be hot to work . Are you saying that the fuse doesn't blow until you connect any one of the 4 O2 sensors??

I think he says fuse blows when zero O₂ plugged in. You need to unplug the TCM (EGS) and you can meausure the wire squid to ground vs. Blow fuses to test.

Four O₂ heater will look like a short on a DMM so leave those unplugged. Unplug the EGS and see if the wire is shorted before putting in a new fuse.

The egs can be opened to check for a mechanical short eg: pin to chassis. I can't remember if egs or DME needed to be drilled open. One uses rivets but a simple machine screw can replace the rivet.


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There's definitely a short somewhere popping that fuse. Whether the o2 runs are connected together or not doesn't make a difference. Just means the short is on the harness before the connections. Which means a little harder to find.

Somewhere you have wires touching each other or shorting to ground making that fuse pop. I would be very surprised if the egs is shorted. That said, unplug the egs and see if the fuse still pops. If it does, it's not the egs.