Can bad 02 Sensor wire cause Limp Mode to Trans?

[KZOO325i]

Hey Guys, Happy Corona- Apocalypse to you all, I hope everyone is cooping well.
My 2002 325i with auto Trans just went into limp mode, feels like stuck in 4th?
I suspect some damage to the O2 Sensor wires? Can anyone confirm this is even possible?
Thanks much for any responses.

[Muzz258]

It could do, might do, don't really know.

If your auto trans has gone into limp mode, you will have the "cog of death" amber warning light on the dash. Time to get a good scanner with BMW software to read the trouble codes in the transmission computer (EGS) and engine computer (DME). Once you get the codes, you'll have the clues needed to fix the problem. Before then, we are all just guessing and you will end up throwing parts randomly at the car in the hope of fixing the problem.

There are many options for a good BMW scanner, here are two:
- Foxwell NT530 scanner with BMW software https://www.foxwelltool.com/wholesal...installed.html

- BMW INPA software (free) running on a windows computer with special cables (cheap) https://www.bimmerforums.com/forum/s...xperimentation

Once you get the codes, post them here along with the descriptions and we can help you.

[dworthy]

+1

No need to guess here, get the codes read and report back, or get the proper tool to read codes.

[KZOO325i]

I have damage to those wires and it coincided with the Limp mode, so educated guess. Exposed wires coming from the front 02 sensor (bank 1 sensor 1?) just after the attachment. Someone mentioned BMW doesn't sell the 02 sensor wires?

[dworthy]

If you are close to the replacement mileage, just replace them IMO. So 100k is the typical replacement mileage, and Amazon sells them (Bosch) for a pretty decent price of less than 200 bucks for the front two.

[KZOO325i]

Im sure they are orig. but its not the 02 sensor thats damaged, its the Wires. I suspect it caused my Trans Limp mode to come on,
and wondering how to fix/splice O2 Sensor wires now.

[dworthy]

A bad or missing signal from the MAF will cause limp mode, as for the oxygen sensors, I just don't know.

[whiskychaser]

Bosch advise against cutting or soldering the O2 sensor wires. That is hardly surprising when you consider the signal voltage only hovers around 1v. If you have got a plausible MAF signal and your mixture is out of scope, the DME will use a stored map and ignore the O2 sensor signals. It will turn on the SES light but that will not result in an issue with the trans. So if the O2 sensor wires are cut, replace the sensor. Then get the fault codes read in the DME and EGS as Muzz 258 suggests.

[KZOO325i]

Thanks for the reply guys. Whiskeychaser: Why would I replace the 02 sensor if the wire to it isn't intact? I can see why they wouldn't advise it, but alas, here I am with a burned wire to it. The Trans Limp mode came at the same time as the burned wire so I expected it to be the cause. Those wires are so small & fused together, I don't see how they could be spliced?

[bluptgm3]

Are you saying that the wires ‘up-stream’ from the O2 sensor connection in the engine harness are bad or the O2 sensor leads to the engine harness are bad?
Either way, I’m surprised the engine itself is not in ‘limp’ mode.

So 100k is the typical replacement mileage, and Amazon sells them (Bosch) for a pretty decent price of less than 200 bucks for the front two.

NTK makes the Bosch sensors. NTK are typically less expensive.



Sent from my iPhone using Tapatalk

[whiskychaser]

Whiskeychaser: Why would I replace the 02 sensor if the wire to it isn't intact? I can see why they wouldn't advise it, but alas, here I am with a burned wire to it. The Trans Limp mode came at the same time as the burned wire so I expected it to be the cause. Those wires are so small & fused together, I don't see how they could be spliced?

Looks like you have answered your own question. If it is still not clear, just consider the wires and O2 sensor as a unit - that is how you would buy one. But before you go shopping, you need to find out why the wire is burned. Has it touched the exhaust or is there a short? You don't want to wreck the DME or cause an engine fire

[KZOO325i]

Yes I need to do further inspection today. The Trans Fuse keeps blowing.

[whiskychaser]

My guess is you have a dead short on the O2 sensor heater circuit and you are blowing fuse 4. That fuse is one of the power sources for the TCM too. If you have not done so already, I'd disconnect that sensor PDQ

[KZOO325i]

Thanks for your reply Whiskeychaser, I hope to be have to get better weather tomorrow to get underneath it.

[KZOO325i]

Update: Yes a frayed 02 sensor wire can cause a Trans Limp mode. I unplugged the bank 1 sensor 1 02 sensor wire, Taped up the frayed ends and no issue with trans now.

[dworthy]

Good to know, thanks for coming back to let us know.

[bluptgm3]

Update: Yes a frayed 02 sensor wire can cause a Trans Limp mode. I unplugged the bank 1 sensor 1 02 sensor wire, Taped up the frayed ends and no issue with trans now.

You may consider ‘self-vulcanizing’ tape IF this is to be a long term repair.

https://en.m.wikipedia.org/wiki/Self-amalgamating_tape


Sent from my iPhone using Tapatalk