hello i have a 2006 gmc 3500 with 6.6 allison automatic last week my trans started shifting very smooth was feeling the shift points before its not slipping i have got on it still works great but the tap shift doesnt work if you put it in manual mode it doesnt show on the dash its drive or first and also the tow/haul doesnt work and the engine brake also dont work i just took it to the shop and the said a shift control in the trans needs changed he thinks but not for sure could you please help thanks
Allison 6sp: tap shifter problems
- Thread starter JG31RACING
- Start date
I don't think that is it. Sounds more like a broken wire in the column. Maybe Ben will show up soon a nd see this.
i have seen this on here about the wire for tow haul but the shop seems to think its that switch because it dont even light up on the dash that its in m mode if it did light up and the gear tap switch wouldnt work i would think that it is a wire but i just dont no where to start thanks
either TCM wiring or bad NSBU is my guess?? (or IMS as they call it on the 6-speed)
Could be bad wiring in the column too; I dont know what the TCM defaults to when it doesnt see any driver-shift-request signal (open circuit) from the shifter. I will look into it.
Could be bad wiring in the column too; I dont know what the TCM defaults to when it doesnt see any driver-shift-request signal (open circuit) from the shifter. I will look into it.
Look for codes. If the tap-shift buttons have lost their connection due to a bad wire, the TCM will throw a DTC about it. Also, sounds like too many things wrong to be a TCM wiring problem. The reason I say this is in the LBZ's, the T/H wires go to the BCM which then sends a Class2 message to the TCM to enter T/H. The Tap-Shift wires go straight to the TCM. Shift lever wiring is possible though. If T/H AND Tap-shift don't work, It's PROBABLY a bad wire (or two) from the shift lever. You said it's only D or 1? So if you go to M you don't get the 1 2 3 (4) 5 6 display? That could be the IMS, but the T/H not working sounds like shift lever wire.