P2806 and the ISM transmission module
Thread Starter
Newbie
Joined: Jul 2023
Posts: 12
Likes: 3
13 gl550
P2806 and the ISM transmission module
We've had some REALLY cold temps in the midwest and when it got into the negatives my GL550 said it was done. Selecting a gear at the stalk, the transmission did nothing. So I suspected the ISM is going bad. I noticed my battery voltage was a bit low so I also replaced the battery with a new one. Today when it was warmer I decided to do a little more investigation with my Autel scanner and I was able to reprogram the ism/servo shift points and got the car to start again and after clearing all the codes (there were a lot, for random things like seats, etc which I suspect was due to low battery voltage) it started working again, car started and I was able to drive it around. I have a feeling I should start the process of ordering another ISM as it seems they're very common to go out and I imagine that driving around in snow and sleet it probably froze the ISM to death. So I would hate to get stranded and I hear towing these cars when that happens is a nightmare as theres no real "emergency" way to get the car out of park without unbolting the ISM and manually moving the shift lever.
Anyone else had a problem like this? Unfortunately my autel model (ms808-bt) cant program the ISM with the vin, I saw in a video that you can take it to mercedes in neutral with the new ISM unplugged and they supposedly will code the new one "free of charge." Any truth to that? If I gotta pay I'd rather just invest in a higher end Autel like the MS906-pro that CAN do the coding.
Anyone else had a problem like this? Unfortunately my autel model (ms808-bt) cant program the ISM with the vin, I saw in a video that you can take it to mercedes in neutral with the new ISM unplugged and they supposedly will code the new one "free of charge." Any truth to that? If I gotta pay I'd rather just invest in a higher end Autel like the MS906-pro that CAN do the coding.
Last edited by KA0TYK; Feb 5, 2026 at 08:08 PM.
Junior Member
Joined: Dec 2022
Posts: 57
Likes: 13
2012 MB R350 Bluetec
I have had the message multiple times where it says "drive to workshop without shifting gears" for 2 months. I am almost certain this is the usual ISM warning message.
We have had very frigid temps last 2 months in Ontario. Other than the scary warning with red illumination, I have so far been fine ignoring it. Car has shifted fine without leaving me stranded.
We have had very frigid temps last 2 months in Ontario. Other than the scary warning with red illumination, I have so far been fine ignoring it. Car has shifted fine without leaving me stranded.
We've had some REALLY cold temps in the midwest and when it got into the negatives my GL550 said it was done. Selecting a gear at the stalk, the transmission did nothing. So I suspected the ISM is going bad. I noticed my battery voltage was a bit low so I also replaced the battery with a new one. Today when it was warmer I decided to do a little more investigation with my Autel scanner and I was able to reprogram the ism/servo shift points and got the car to start again and after clearing all the codes (there were a lot, for random things like seats, etc which I suspect was due to low battery voltage) it started working again, car started and I was able to drive it around. I have a feeling I should start the process of ordering another ISM as it seems they're very common to go out and I imagine that driving around in snow and sleet it probably froze the ISM to death. So I would hate to get stranded and I hear towing these cars when that happens is a nightmare as theres no real "emergency" way to get the car out of park without unbolting the ISM and manually moving the shift lever.
Anyone else had a problem like this? Unfortunately my autel model (ms808-bt) cant program the ISM with the vin, I saw in a video that you can take it to mercedes in neutral with the new ISM unplugged and they supposedly will code the new one "free of charge." Any truth to that? If I gotta pay I'd rather just invest in a higher end Autel like the MS906-pro that CAN do the coding.
Anyone else had a problem like this? Unfortunately my autel model (ms808-bt) cant program the ISM with the vin, I saw in a video that you can take it to mercedes in neutral with the new ISM unplugged and they supposedly will code the new one "free of charge." Any truth to that? If I gotta pay I'd rather just invest in a higher end Autel like the MS906-pro that CAN do the coding.
Newbie
Joined: Feb 2026
Posts: 2
Likes: 0
From: Pennsylvania
DURAMAX 2500HD
Try unhooking the battery with key on engine off overnight. Or unplug ISM about 2 minutes, then plug it back in electrically. You may have to remove an under-belly shield to access plug. Driver side of transmission case. I am struggling with my Metris, we also are having very low temps. However, she is in a 65* shop & Autel cannot code on these vehicles. Autel can retrain ISM and shifter on column. Dealer claims we cannot buy ISM (not allowed) and we are in business since 1989.
