Allison 5sp: P0748 and can't find the problem

[BombDocDiesel]

This is kicking my butt. I have pulled the entire harness apart looking for shorts or abrasions. I have also used the DVOM to check each wire from the connectors to the TCM. I pulled the VB over the weekend and checked the internal harness and the solenoids. I had a spare VB laying around and ran the same tests on it with the same results. I even went through the entire checklist in the ATSG with the DVOM. I can't find anything wrong. Is it possible that I have a bad TCM? I bought a new one so I can keep trouble shooting. I'm still waiting for a new flash so I can re-load the TCM I have just to make sure.

 

[Mike L.]

This is kicking my butt. I have pulled the entire harness apart looking for shorts or abrasions. I have also used the DVOM to check each wire from the connectors to the TCM. I pulled the VB over the weekend and checked the internal harness and the solenoids. I had a spare VB laying around and ran the same tests on it with the same results. I even went through the entire checklist in the ATSG with the DVOM. I can't find anything wrong. Is it possible that I have a bad TCM? I bought a new one so I can keep trouble shooting. I'm still waiting for a new flash so I can re-load the TCM I have just to make sure.

Give me a call.

 

[BombDocDiesel]

Is there a difference between internal harnesses in the 5 speeds from different years? I have two VBs and two harnesses. One is black and the other that almost clear/yellowish looking color. We tried the new TCM, no codes now but no transmission either.

I'm about to ask Destroked if they changed their external stand-alone harness configurations since mine was made. This is driving me crazy. It looks like I won't be driving it before heading to the sand box.