2011 GL 450, 151k miles. Owned by me for 11 years.

On occasion, my vehicle enters limp mode. After starting, it will shift into drive and reverse and park, but shifts hard and will not change forward gears. For several months when this would occur (maybe once in 20 starts), there would be no MIL lights.

I know it will occur before I even start the engine:
How do I know? When I switch the ignition to the "ON" position, the front parking sensor lights on the glareshield all illuminate (this is normal). The lights should all extinguish upon initialization (proximity lights and activation lights in the middle). However, when the transmission is going to act up, the parking monitor system will not deactivate -- the lights remain on and are trying to measure the distance to surrounding objects (you'll also hear the activation beep). I should not hear this until I put it into gear with the engine running. In other words, it thinks it's in gear, but it's not (and engine not running). I know this actually means the CAN bus components have no idea what gear it's in.
**The kicker is, I can turn the ignition switch one click to the left (to "ACC") and then turn it back to the "ON" position and the parking monitor system behaves normally. At that point, I can start the vehicle, and it drives perfectly. I have never had it display this weird behavior on multiple subsequent starts.

Battery health:
Not too long after it started occurring, I checked the UB voltage on the display and noticed that resting voltage was 11.9 volts ... I know the battery was toast at that point. It had begun to crank slowly. So, I replaced the battery.
**The condition quit occurring for about 2 weeks. I thought "great, that was the problem" ... Well, that did not solve the problem. It reared its head again after that 2-week hiatus ... same frequency.

FINALLY, a couple of weeks ago, I got a check engine light when it misbehaved and plugged in a basic OBDII scanner that I have. Code U010187. TCM communication problem. The dealer is just right down the street, so I restarted the vehicle and drove right to the dealer. Ultimately, they said I have a bad TCM/conductor plate. They ran STAR diagnostics and confirmed the code. Then they cleared the code and reran the diag. The code did not reappear and has not since.

My question to this group:
They want $5k to replace the whole valve body (which they don't recommend because of mileage -- they want me to replace the whole tranny for $10k). I have had the dealer service this tranny every 40k miles by the book, and they had just serviced it a few months ago. The thing shifts like butter and always has. I'm not sure I'm fully on board with a bad conductor plate. The reason is, there are no speed sensor or turbine codes or anything like that in the STAR report. When they cleared the codes at the dealer, the TCM had a C103 code stored (not active), but that's for the shifter. I honestly don't think the shifter module is bad either.
**What do y'all think? Has anyone seen this U010187 code with no corresponding speed sensor or turbine speed codes from the TCM itself? I don't want to either have the dealer install a whole valve body OR have me drop the pan on the tranny and take the conductor plate off the valve body and send it to one of these board repair shops just to have this problem persist. Anywhere else I should be looking on this vehicle? Should I just trust that the dealer has thoroughly evaluated the problem and believe them that the conductor plate needs to be repaired/replaced?

Thank you!
Russ

 

You gotta get a real Mercedes scan tool to read this out. He OBD two readers with generic one directional capability, will lie to you.

It’s very likely the conductor plate and if you don’t want to spend the five grand on a new one at the dealer, you can send a virgin one to a third-party for programming to your van for about five 600 bucks.

Or you could just go the cheapskate Way drop the pan and shoot some electronics cleaner at the contractor plates, sometime they just get gummed up or varnished over which is what causes this error.

I had this happen in a prior GL and a tranny flush staved off the problem for a while.

 

Thank you so much for the response. When the Check Engine light came on (the only time it has), I rushed it to the dealer. They did a full STAR diag on it (twice) and gave me the full printouts. There were a bunch of stored codes, but nothing active other than U010187. When they cleared the active codes and ran the STAR diag the second time, the TCM reported no internal stored codes (no speed sensors or turbine speed issues, etc.). Lots of other modules indicated they couldn't talk to the TCM on the first run, but that was all resolved the second time.

I'm wondering if I've got bad wiring to the TCM or some relay that doesn't want to engage on initial power up. Again, this never occurs on the road, just at start up. When the aforementioned light show occurs, we know to just reset the ignition. I would think the TCM would give us more info about what's going on.

I may try to have my board repaired, or try for the virgin board. Any recommendations on a business that could program a virgin unit? I'm not sure the dealer would do it at all if it wasn't purchased through them.

Thanks!