Trans won't go in fwd or rev

[Chris611]

Yesterday I was sled pulling and the second pull, when I got to the end of the track, the transmission would not go in rev. I tried forward and it wouldn't do that either. I shifted to neutral at the end of the pull like always. The shifter on the column moved easier than normal. There wasn't near the drag that there normally is when shifting between R,N,D. Also when I went to Park, the doors didn't unlock like normal. I ended up shutting the truck off and then it all worked fine. I have no codes.

Any thoughts on what happened?

 

[Mike L.]

Sounds like the main linkage cable came out of its retainer. See if the cable if flopping around under the truck.

 

[Chris611]

Thanks Mike.

I just went out and looked under the truck and the cable is still in its retainer. The shifter felt loose when it wouldn't go in gear, but after I shut the truck off and started it back up, the shift then had "normal" tension. Drove it home with no problems.

It was like the truck didn't know I was moving the shifter. The door locks didn't cycle when I went into and out of Park like they would normally. Seems like an electrical/TCM deal.

 

[Mike L.]

NSBU needs to move before the door locks will work so this tells me the cable wasn't moving the lever on the Alli or. something came loose inside where the linkage comes through the case.

 

[Chris611]

Could this be the neutral safety switch? It would explain the no lock and unlock when I put the shifter in Park. I looked an my neutral swtich is black with a single connector. This seems like a new style. Do they still have issues?

EDIT- sorry mike, I was posting at the same time as you.

Where should I look on the cable? I felt the down by the tranny and it felt solid. Is there an area where I should look for a cable problem?

 

[Chris611]

Mike, I had the plastic off around the column and it appears that the shift cable is secured from the column to the trans. Is it true that the transmission will go into rev and 3rd even if the NBSU is not hooked up or functioning properly? Or will the TCM disable the trans if it doesn't see the NSBU output?

 

[Mike L.]

Mike, I had the plastic off around the column and it appears that the shift cable is secured from the column to the trans. Is it true that the transmission will go into rev and 3rd even if the NBSU is not hooked up or functioning properly? Or will the TCM disable the trans if it doesn't see the NSBU output?

Disconnecting the main harness connector in back of trans will give you 3rd and rev. This is an induced limp mode.

 

[ripmf666]

Mike I know on my 01 2500 with the 8.1 and Allison I had to replace the main shift cable,Went under the driver side plastic step cover it was stretched out and not going into gear all the way, Do we still have that on the newer truck and can that cause this to happen?

 

[Mike L.]

Mike I know on my 01 2500 with the 8.1 and Allison I had to replace the main shift cable,Went under the driver side plastic step cover it was stretched out and not going into gear all the way, Do we still have that on the newer truck and can that cause this to happen?

Yes. I would check the cable from the column to the trans and see if everything is tight and in place.

 

[ripmf666]

Ok so this info might help him out some.

http://www.duramaxdiesels.com/forum/showthread.php?t=15090

http://www.duramaxdiesels.com/forum/showthread.php?p=234385#post234385

 

[Chris611]

Disconnecting the main harness connector in back of trans will give you 3rd and rev. This is an induced limp mode.

So since I couldn't get it to go into reverse, this rules out the NSBU as being the problem, correct? When this happened Sunday, I remember seeing the line under the PRND31 indicating the correct gear. It was following the column shifter. The trans just would not go in gear. I am assuming this is electrical since shuting off the truck and then restarting it fixed it. Is there anything mechanical that would fix itself by restarting the truck?