I have a 2006 C5500 Kodiak 6.6 with a check transmission light and loss of exhaust brake and speedo cuts out. Had lost communications with the TCM and had a used one reprogramed by Allison repair shop. Now the check engine code is gone for the TCM. The check engine light is for loss of communication with GPM . Went to town for first voyage after replacing the TCM and it did not seen to want to shift out of first gear so turned around for home and disconnected the batteries for twenty minuets and tried again and seemed to be fine but got to the outskirts of town and lost the speedo and the light with wrench and gear came on and limped it to where we were going and let it sit and restarted and ran normal. Went to advance auto and read codes and still only had GPM code. Also drove it around thirty miles after this and lost the speedo for just a second and everything else was still normal. I have seen other posts with similar things but they don't come back and say what fixed it.
wrench and gear light
- Thread starter bwedge
- Start date
Update. I replaced the speed sensor thinking that would fix the speedometer issue but it didn't. Drove about five miles and the speedometer dropped out and came right back up but it stayed in fifth gear and no engine brake to help stop it. Had to give it a lot of pedal to get to a place to pull over. No wrench and gear light this time. Let it sit a couple minutes and restarted and back to normal.
Need to go back to the Allison shop or somewhere that can get codes from the TCM. I assume GPM is the glow plug module? You're on the right track with the speed sensor, check out the wiring for it as well as the connector at the TCM. Pins could be damaged or dirty, get some male pins and do a drag test on them when the connector is off