Mercedes-Benz Forum banner
Cancel
Create thread New Garage Forums

w210 limp home mode, transmission won't shift, bad battery

Jump to Latest
36K views 14 replies 8 participants last post by  Paulv5  
T
#1 ·
I hope this post helps others with the W210 transmission limp home mode issue. I recently had two problems with my 2002 W210. The first problem was that the SRS light came on. The second problem was that the automatic transmission would not shift out of what I thought was 1st but was probably second. The problem with the transmission occurred on the first start of the day after a cold night. The car has 57,000 miles on it. I searched the forums and the most common source of the transmission problem seemed to be the shift module switch inside the car. The most common source of the SRS problem seemed to be the seat sensor in the passenger seat which controls whether the passenger side airbag is activated. Since I have an Easy Care warranty I decided to take it to the local dealer. The dealer diagnosed the problem as a bad ECU unit for the transmission and a bad ECU for the SRS. The transmission ECU was $1,250.00 plus $205.00 labor. The SRS control unit was $792.00 plus $346.95 labor. To its credit, Easy Care paid for both repairs. I drove the car home. The next day I didn't drive it much but the following day I began having the same transmission limp home mode shift problem, except this time it would happen every time I would go to drive the car, probably about 4 times that day. I would have to pull over, turn it off and turn it back on to get it out of the limp home mode. Today I went to start the car to take it back to the dealer and the battery almost wouldn't turn over the motor. After a couple of tries the car started. On the way to the dealer I stopped for gas. When I left the gas station the car was in limp home mode again. I pulled over to do the restart routine to get it out of limp home mode, this time the check engine light came on. I turned it off again waited 10 seconds and restarted it. The car then shifted normally but the check engine light was still on. When I got to the dealer, I told the service rep I thought the battery was going bad and that was the source of the problem. Couple of hours later the dealer confirmed the battery was bad. The service rep said they were getting all sorts of low voltage codes. The battery was replaced and the car is running fine so far. The first time I took the car in, I told the service rep I had read a post where a guy was having similar problems with the car going into limp home mode on cold mornings and it was eventually determined that the battery was going bad and the low voltage was causing the car to go into limp home mode. The service rep is telling me that the transmission ECU unit was definitely bad and it is just a coincidence that my battery also went bad. The SRS light has never come back on again since the SRS control unit was replaced. My recommendation for anybody having problems with their transmission going into limp home mode is to check your battery. I would expect that this would be a common problem and I am surprised that the dealer didn't check the battery first. I would also suggest that the Mercedes-Benz 722.6 transmission FAQ sticky in this forum make mention of a failing battery being the potential cause of the transmission going into limp home mode.
 
#4 ·
Thanks for the tip.

Did the dealer run the full Star diagnostics? If they did a bad battery would have surely have shown up. Maybe you got a rookie tech who didn't know how to use it. Furthermore there are some dishonest dealers out there and yours might have milked the warranty company.
 
T
#5 ·
I'm not sure if they ran the full diagnostic or not. They ran some sort of diagnostic which was apparently good enough for the warranty companies rep. According to the dealer he had to come by and approve the repair because of the amount. Just to clarify I'm not saying the ECU unit did not need to be replaced. The dealer could be right. I'm not a Mercedes tech. I just suspect it was related to the battery based on the post I read which indicated a bad battery caused the limp home mode problem in that case and the fact that the problem persisted in my case until the battery was replaced. By the way the car is still running fine since I returned to the dealer and they replaced the battery.
 
T
#7 ·
I'm don't know how the star diagnostic system works and whether for example low voltage codes are stored or what the threshold is to trigger a code. If there not stored and the battery was just starting to go bad at the time of the first visit to the dealership, I guess it is possible the approximatley 30 mile drive to the delearship could give the battery a sufficient charge so that it would not generate a low voltage code at the time the diagnostic was performed. This seems consistent with the battery discharging some over night and causing the limp home mode problem initially only on the first start of the day. Maybe someone in the forum with more technical knowlege can confirm whether or not this is possible.
 
P
#10 ·
I do know if this will help, but all the previous comments on the battery voltage are important. On our model of cars anything less than 11 volts will cause problems.

As more and more electronics are placed on the cars voltage availability becomes even more important.

I think it's the 211 or maybe it's the 212 but there are two batteries and they have placed a battery control module in the system to monitor and shut down users as the battery ages and alerts you to that fact.

Therefore a good healthy battery is very important!!
 
F
#9 ·
Did happen to my 2000 E320 2 years back. Started one morning, stuck in 2nd gear, no gear selector light. Drove to an indy with SDS. Low battery voltage confirmed on the SDS. Replaced the battery and cleared all the codes. So far so good. Our car is run by electronics. Low voltage battery = low current to the electronics. I am no MB tech, just speaking from experience. Just my 0.02.
 
T
#12 ·
For what it is worth here is another post with the same problem:

Primary said:
I am so bad for providing details about my issue. Hopefully my explaination will help someone out there some day...

I had this issue. Car would not upshift in the AM. Could not force it by reving past 3000 RPM or driving faster than 30 mph. My only remedy was to pull over, stop the car, and restart the car. Then, problem was gone the rest of the day.

Sun goes down.. Moon comes up.. Sun comes up again... BOOM.. problem happens again.

Here is what the deal was. BAD/OLD BATTERY

The reason this would happen for the first start of the day was that by then, the battery had time to lose just enough charge for the car's computer to pick up a low voltage alarm. Once that alarm is triggered, the car goes into a 'crippled/limp' mode and does not let you get out of 2nd gear, even if the battery charges a little and gets lifted back into the correct voltage range. The alarm persists.. until the car is turned off.

When I was stopping the car and restarting, the battery now was able to give the car's computer a rating in the proper range. Therefore, limp-mode was not being triggered and I was able to go about my day.

Eventually, my battery just could not hold the correct voltage and my restart technique was no longer a viable option. Took the car to my Mercedes mechanic, he found the low voltage code in the computer, changed the battery (damn expensive deep cycle batteries!). I'm back on the road.
Click to expand...
 
C
#13 ·
this post has been very helpful as i'm having a similar issue, except i'm also triggering a p0748 code and my car won't leave limp mode. my car died at a stop light and wouldn't move in any gear, so i tightened down the battery terminals and voila it will shift into gear but stuck in limp mode

i've read online that my problem is probably a mismatched ETC module (i did a tranny/engine swap) so i will try to test that as soon as possible

is the general consensus here that once limp mode is triggered by a bad battery, the transmission is no longer in limp mode once the battery is replaced? my car won't leave limp mode no matter what so i'm thinking my problem was a mixture of badly connected battery and also mismatched ETC module, any feedback would be great
 
#15 ·
The conductor plate needs to be checked. $5 ELM327 Blutooth & Torquepro yeilded speed sensor code for me. Clear the code & see if normal trans. Relatively straight to change. A few more steps than a trans fluid/filter change. Requires remove valve body to replace plate. Scanner fault shows up as a tranny speed sensor failure. Been a while but I've done three of these and completely cured problem. Also replaced conductor plate plug on passenger side of trans. Used Valvoline Maxlife ful synthetic.

Hope tjis helps.
 
Mercedes-Benz Forum
posts
7.8M
members
748K
Since
1999
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!
Full Forum Listing
Explore Our Forums
W126 S,SE,SEC,SEL,SD,SDL Class R/C107 SL/SLC Class W163 M-Class W124 E,CE,D,TD Class W210 E-Class