2001 ML320 STUCK in Limp Mode, have Searched! - PeachParts Mercedes-Benz Forum

johnathan1 · #1 07-28-2016, 02:05 AM

Ok, I'm not sure if I should start a new thread, so I'll just ask here first.

My particular 2001 ML320 has a check light, BAS light, flashing Low Range light on startup and is stuck in limp mode.

I am getting codes:

C1142 - Lateral Acceleration Sensor, Open/Shorted

different module:
P2061-004
P2061-016
P2061-064

New codes from today:
P114214
P102400

I have replaced the conductor plate, 13-pin connector, and renewed fluid and filter. I also repaired melted wiring going to the 13-pin connector.

None of this made any difference.

Clearing the codes doesn't make any difference. The lights stay off for about a minute, then come back on.

I'm at a loss with this one. I am assuming the Acceleration sensor is a separate issue and will not put the car in limp mode?

Could I be looking at a bad TCM? When I try to access the "Transmission" computer in my scanner it only says "Communication error".

TimFreeh · #2 07-28-2016, 07:43 AM

The melted wire going to the 13 pin connector kinda caught my attention.... How did it get melted? Have you run continuity checks between the 13 pin connector and the transmission ECM to verify that you don't have more than 1 melted wire?

johnathan1 · #3 07-28-2016, 03:25 PM

All 13 of them apparently got melted when whoever replaced the catalytic convertors didn't replace the heat shield. I cut, and resoldered each one and replaced them.

I'm thinking all of those wires shorting on each other may have destroyed the TCM, but when I disconnect that particular box, the instrument cluster shift readout disappears, and reappears when plugged back in. So it is definitely doing SOMEthing, but it's hard to say if it's working 100%. Is there a way to test the TCM other than looking for specific codes?

TimFreeh · #4 07-29-2016, 08:54 AM

If you can't communicate with the TCM with your scan tool there is certainly some sort of issue. Can't really say if the issue(s) is related to faulty wiring between the transmission and the TCM, or a damaged TCM caused by previously damaged/shorted wires.

What kind of scan tool are you using?

I don't think a faulty lateral acceleration sensor will cause the transmission to go into limp-home mode but I do know that if a 722.6 enters limp-home mode with certain stored fault codes it will NOT reset itself after the condition that caused the limp-home mode is corrected.

To get it out of limp-home mode you must erase the codes and reset the transmission using SDS or another appropriate scan tool. If you can't communicate with the TCM this is going to be a bit problematic.

johnathan1 · #5 07-29-2016, 12:49 PM

I am using an iCarsoft scan tool specifically for MB. I believe this one should have no problem erasing codes and pulling the car out of limp mode.

I can't seem to communicate with the TCM at all, even though all wiring now appears to be sound and the TCM itself looks perfectly fine, as does all of it's wiring. No fluid ingress, nothing at all.

What could be causing this? Is there something here I am overlooking? I would think that as long as the wiring to the transmission and the TCM are sound, then it should be able to communicate, correct? Other reason would be a totally dead TCM, but how often does that happen? Also, why would my shift indicator work with TCM plugged, and not without it? Surely that has to be a sign that it is at least powering on?

johnathan1 · #6 07-29-2016, 12:52 PM

Oh, and another thing...

If it WERE in fact a dead TCM, wouldn't it throw a specific code for that? (maybe one of my other codes that are unspecified??) The only code that offers a description is the Lateral Acceleration Sensor, the rest of the codes I can't find any information on AT ALL! Could this be a clue?

TimFreeh · #7 07-29-2016, 03:18 PM

The lateral acceleration error code is being generated by the ESP system, it has nothing to do with the TCM problem or the limp-home mode.

I don't think there is a 'dead TCM' code but even it there were you'd have to get in contact with the TCM to determine it its dead right? The fact that you can't establish communications with the TCM means one of two possibilities
1) the TCM is dead or the wiring to it is faulty. BTW the wires you repaired wouldn't stop a scan tool from communication with the TCM because on this transmission the TCM isn't housed in the transmission like the later 722.9 versions or 2) your scan tool isn't capable of communication with the TCM.

I'm not familiar with the icarsoft scan tool but in earlier years I used a Snap-on MT2500 and it would not always reliably communicate with all modules of the different cars I worked on. I do remember it being able to communicate with TCM's in W210 but not in a W202 even though they used the same 722.6 transmission. I also had troubles communication with airbag modules, sometimes it would work and sometimes it wouldn't work.

I would say its a good sign that the range recognition works when you plug in the TCM and it doesn't work with the TCM disconnected since transmission range information on this car is CAN related.

Have you ever used the your scan tool to access other MB TCM's? Do you know an independent shop in the area that has the real MB SDS scan tool? You're not going to fix this problem until you can establish communication with the TCM.

johnathan1 · #8 07-30-2016, 04:02 AM

I was pretty sure the C1142 code wouldn't limp the car, but since it was basically the only code I was able to decipher, that maybe it was worth asking.

You are absolutely right that it could be the scanner. I'm taking it to a friend tomorrow who has MB SDS and will update.

Thank you SO much TimFreeh, for giving this issue your attention and a second set of eyes.

johnathan1 · #9 07-30-2016, 08:34 PM

Well, you were right! My particular model isn't supported on this scanner for accessing the TCM. (Gee, why not??) So I will be returning it.

Anyway, I took it to a friend with a Snap-On Solus ultra and we pulled the TCM codes. Had no problem communicating, there were TONS of codes stored. At least 15 in the TCM alone! Cleared them all, only one came back, a code for the "Transmission Temperature Sensor" which appears to be stuck at 210F degrees. Shorted wiring to it??

After codes were cleared it would shift somewhat normally, but still harsh into drive, and didn't really feel "right". It shifted kind-of "ok" for about a half mile then went RIGHT back into limp mode. At first I could just turn it off and then back on, then it was stuck again after about three cycles. I didn't notice any slippage or anything like that, and it was shifting, just not properly. It would shift late, and jerk into first when coming to a stop.

So, NOW my question is, would a bad temp sensor cause these types of issues/limp mode? I couldn't go back and scan again after driving to see if anymore codes came up since he had closed up shop for the weekend.

Quote:

Originally Posted by TimFreeh

The lateral acceleration error code is being generated by the ESP system, it has nothing to do with the TCM problem or the limp-home mode.

I don't think there is a 'dead TCM' code but even it there were you'd have to get in contact with the TCM to determine it its dead right? The fact that you can't establish communications with the TCM means one of two possibilities
1) the TCM is dead or the wiring to it is faulty. BTW the wires you repaired wouldn't stop a scan tool from communication with the TCM because on this transmission the TCM isn't housed in the transmission like the later 722.9 versions or 2) your scan tool isn't capable of communication with the TCM.

I'm not familiar with the icarsoft scan tool but in earlier years I used a Snap-on MT2500 and it would not always reliably communicate with all modules of the different cars I worked on. I do remember it being able to communicate with TCM's in W210 but not in a W202 even though they used the same 722.6 transmission. I also had troubles communication with airbag modules, sometimes it would work and sometimes it wouldn't work.

I would say its a good sign that the range recognition works when you plug in the TCM and it doesn't work with the TCM disconnected since transmission range information on this car is CAN related.

Have you ever used the your scan tool to access other MB TCM's? Do you know an independent shop in the area that has the real MB SDS scan tool? You're not going to fix this problem until you can establish communication with the TCM.

TimFreeh · #10 07-31-2016, 02:34 PM

I would not think that a error code for the ATF temp sensor would cause limp home mode. I do know that the ATF temp data is used when the TCM is formulating shifting strategies but I don't think it would be so important as to cause limp home mode.

When I use SDS to monitor ATF temps the data is always reported in celsius, was the snap on scan tool reporting 212F? In the 722.6 the ATF temp sensor is wired in series with the P,N reed contact switch. For the TCM to get ATF temp info the car must be in "D" or "R", if the car is in neutral or park the TCM will not receive ATF temp data and I believe it defaults the ATF temp to whatever the engine temp.

In looking at my Intro to the 722.6 manual there is a table that shows DTC's that will cause limp-home mode and the ATF temp error indicates that it would not cause limp-home mode but then references footnote "C". Footnote "C" states "with implausible signal input, control module defaults to a variable substitution value (with loss of one rear speed sensor input)"

It's not really clear to me why the loss of ATF temp data would result in losing data about the rear speed sensor situation but if true I could certainly see the lose of a rear speed sensor immediately causing limp-home mode.

I'd go back and see what codes show up in the TCM.

Zulfiqar · #11 08-01-2016, 12:49 PM

I would suggest you remove the 13 pin connector and look at the pins closely with a light and magnifying glass, it maybe that the connector has damaged pins.

johnathan1 · #12 08-03-2016, 04:33 AM

Still haven't looked into this further. Too many customers cars to repair before I can get to my own. I will post once I have more information.

It is likely there are more codes now that it has been driven, will have to recheck later. I have been in contact with iCarsoft and I have to say, they are very helpful, but haven't been able to provide a solution for me. Will see what their engineering department has to say within a few days hopefully.

I checked the 13-pin connector, it looks perfectly fine.

Zulfiqar · #13 08-08-2016, 11:57 AM

if you can retest the codes - it would point to the right direction. The speed sensors acting up can do this. Both of them are built into the conductor plate. You might want to scope the sensors to see if you lose a pulse while moving. If you do then you found your issue.

The deeper level error codes are 2 digit and change if the code goes from active to pending.

johnathan1 · #14 08-27-2016, 10:29 PM

SOLVED

I replaced the wiring going to the 13-pin connector, reset codes and all is well.

tyl604 · #15 08-27-2016, 10:57 PM

What do you mean about repairing the wiring? Did it not work to repair the wiring in the first post and did you later just install a new set of purchased wires?