I recently had a new conductor assembly put in the truck as well as a new shifter (used shifter, new to the truck). Car was running fine for a week then Sunday, started the truck and it would not shift out of 2nd gear. I would guess it's limp mode but there was no CEL. Shut it down, came back 3 hours later and tried again. Still wouldn't shift out of 2nd and still no CEL.

Took the truck back to the shop on Monday and it drove fine on the way there. After them having the truck for 2 days, the report from the shop is that there are no engine codes, no transmission codes and the truck is driving fine for them every time they test drive it. What the $%^& could it be? The shop owner said if the truck had been in limp mode, there would be evidence of it and there isn't and code indicating limp mode.

Any ideas?

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1999 ML 430

Brake light switch. If it shifts out using the override and then it operates normally, it's probably the brake light switch. See if the brake lights work. Even if they do work it could still be the switch, because there are 2 sets of contacts. One will let the brake lights work (the normally open contacts), if the normally closed set go out the brake lights will work, but the shifter and other components of the truck need to see both sets working.

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Interesting, thanks for the suggestion. For ~$15 it's definitely worth a shot. I'll update after I replace it.

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1999 ML 430

BTW, would this throw any kind of code? There's nothing in the ECU or TCU.

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1999 ML 430

Most likely the shifter!

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How would you test the shifter to see if that's the problem?

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1999 ML 430

Of course the ONLY way to prove that is when the trans IS in limp mode.
And then a MB scanner is required!

You would have to monitor live data in the trans ECU & see what gear the shifter shows.

It would show "2" instead of "D"...and that would not set a code!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Ok, now I see why he has wanted to keep the car. He's test driving the truck trying to get the live data when it happens again.

He was a MB tech for 10 years and his shop is a Mercedes only shop so I'd bet he has the MB scanner. Sounds like you are most likely spot on with the shifter. I'm assuming that problem could present as intermittent?

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1999 ML 430

This is a quote from your original post.

"He has diagnosed the problem as a defective gear shifter module. $882 to replace new and $640 to replace with a used part...."

Correct me if I'm wrong, but didn't we find that the shifter in your ML is the early version, which uses the gear recognition switch, and not the later ESM type?

Also, I believe your problem began after the conductor plate was replaced, right? If so, the new conductor plate may be the problem.

Assuming that all the diagnosis/work performed up to this point has been done properly, the next thing to do is check the four signal wires from the gear selector switch to the transmission ECU. Depending on the position of the shifter, the voltage at each of these wires will be either >11 or <1. These inputs let the trans ECU know what gear is selected. If one of these values is implausible the transmission goes into "limp" mode.

Correct. The shifter is the early model with the GRS, not the ESM.

I don't think it's the conductor plate issue because... The conductor plate had been having issues for a while. As I was getting ready to take the car in for repair for that, the reverse lights would not go on. The fuse was ok, the bulbs were ok and it was determined that the gear recognition switch was the problem. The mechanic I was referred to botched the job pretty badly and I had a second mechanic complete the repair but I'm not sure how well he did it. So, I'm guessing that the problem that happened after the conductor assembly was replaced could have been lingering as a result of the botched replacement of the gear recognition switch in the original shifter. The shop owner replaced the shifter with a used shifter.

As to why it's happening with the replacement shifter, the only thing I can think of based on what I've been told here is that the new/used shifter I got may be faulty?

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1999 ML 430

Make sure he has a "scanner" that can read the "Actual Values" as well as the transmission "Adaptation Data".

The actual values will tell him, among other things, if the trans ECU know the position of the shifter. The adaptation data will tell him if one of the shift members (inside the transmission) is to blame.

Thanks, I'll ask him the above tomorrow and report back.

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1999 ML 430

Here is what the shop owner just emailed me. I've been updating him all day with all the suggestions here.

"Yes I have the same dealer Mercedes scanner as the Mercedes dealer has. I checked out all this. I dont see any problem at this time its working perfectly fine. I have 6 month warranty on your gear shifter. I believe you can drive your car without any problem. please do call me or stop by to pick up your car. Thanks."

If I tell him to put a brand new shifter in the truck, not a used part like he did previously, would that most likely solve the problem? To say I'm irritated with his response is an understatement. I don't see why he would think the truck is ok and that it won't happen again.

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1999 ML 430

I just re-read this... If it's a shift member inside the transmission, is that a huge deal to repair? It sounds like it.

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1999 ML 430

Your guy said everything looks good, so apparently that's not your problem.

If it were, it would require a tear-down and inspection.