Dreaded trans. Failsafe prog.

[Oldmactech]

Thanks. I went through the O2 wiring this am and all looks good. I don’t exactly know how to test the continuity on the O2s but am checking in the manual to find the O2 power connectors. I did disconnect both upstream 02’s and started the car and yet another fuse blew. Not a good test but that somewhat tells me the O2’s are not the problem but still tracing.

I did reclean and reconnect the TCM wiring, blew the fuse again. I suspect the TCM is the culprit. Haven’t found the trick to remove it from the container but I trust that I’ll figure it out.

I did notice that one of the harness connectors to the TCM contained a few wires that apparently had either been spliced or repaired as evidence of clear shrink tubing. Normal?


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[TheFixer]

Originally Posted by Oldmactech

Thanks. I went through the O2 wiring this am and all looks good. I don’t exactly know how to test the continuity on the O2s but am checking in the manual to find the O2 power connectors. I did disconnect both upstream 02’s and started the car and yet another fuse blew. Not a good test but that somewhat tells me the O2’s are not the problem but still tracing.

I did reclean and reconnect the TCM wiring, blew the fuse again. I suspect the TCM is the culprit. Haven’t found the trick to remove it from the container but I trust that I’ll figure it out.

I did notice that one of the harness connectors to the TCM contained a few wires that apparently had either been spliced or repaired as evidence of clear shrink tubing. Normal?


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The spliced in looking wires are normal.

You need to follow those o2 wires to the dme. Pre and post wires. The short could be before where the wires disconnect. Mine was. Buried close towards the firewall on the edge of the back exhaust header.

TCM comes out pretty easy. There's little plastic clippy things that you press on so you can slide it out.

I have a couple spare tcms. 30 bucks plus shipping if you do need one. You can code it with pa soft.

I really doubt the tcm is bad though.

[Oldmactech]

Thanks. So your short was near the TCM? The O2’s are on a harness connector that plugs in to the TCM?


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[TheFixer]

Originally Posted by Oldmactech

Thanks. So your short was near the TCM? The O2’s are on a harness connector that plugs in to the TCM?


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My short was near the back of the valve cover. The wire harness was laying on the exhaust manifold. It burned through.

https://youtu.be/funoO_3PTeU

[TheFixer]

Originally Posted by Oldmactech

Thanks. So your short was near the TCM? The O2’s are on a harness connector that plugs in to the TCM?


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There are 4 o2 wiring runs. They go to the dme. But power is supplied through that fuse that is also supplying the egs. Aka....tcm

[Clavurion]

Actually it's the voltage for lambda sensor heating (all four) which comes from that E-box fuse F4 and also to EGS (TCM as you call it). A wire from that fuse and wires to those loads are connected together (X6962) and bundled in the E-box wiring. So they are not connected to DME. So if you want to investigate the cause of that burning fuse you can separate the wires (red/white) from that bundle and measure which one is shorted. As you can see in that diagram the lambda sensor heating has 0,5 mm2 wires and both supply wires to EGS are 1,5 mm2.

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

[TheFixer]

Originally Posted by Clavurion

Actually it's the voltage for lambda sensor heating (all four) which comes from that E-box fuse F4 and also to EGS (TCM as you call it). A wire from that fuse and wires to those loads are connected together (X6962) and bundled in the E-box wiring. So they are not connected to DME.

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

Awesome.... thanks for clarification.

[andrewwynn]

It also goes to my aftermarket angel eyes


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[Oldmactech]

Thanks very much.
So, the red/ white stripe wire from the f4 fuse is shorting? Measure continuity and resistance from the male pins at the O2 connectors? Will it display voltage with the key in pos2? Not crazy about starting the car with me laying under it.

Do the downstream O2’s have the same connectors, not seeing any?

I have 3 of the 4 O2’s disconnected, fuse 4 still blows.


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[andrewwynn]

Measure from the red/white to ground. It will be a pretty low resistance though the four O2 heaters. Unplug them all and then you should get a fairly normal resistance. O2 heater is about 2 Ω which is practically a short. 12/.5=24A from all four.

The connectors for post cat sensors are both on top of the motor the pre cat are above the exhaust manifold. Keep track which came from where with some tape etc.