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Gm Tech Cam
Gm Tech Cam, Service Technician
Category: Transmissions
Satisfied Customers: 29457
Experience:  11 years experience, specializing in Trans, Elec and Dmax
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Chevrolet Silverado 2500 HD LS: I have an 01chevy 2500hd duramax/Allis

Customer Question

I have an 01chevy 2500hd duramax/Allison lost shift indicator and trans temp , I've replaced the nsbu switch (tan) any good ideas ? Thanks Jason
Submitted: 2 years ago.
Category: Transmissions
Expert:  Gm Tech Cam replied 2 years ago.
Hello, I'm Cam.
Good morning Jaskn. I am sorry for the delay, I was offline and thought someone else would assist you. As they have not, I will gladly.
Other than the display being out, does the transmission shift properly? If so the. It's not a switch or wiring issue. This is why, the computer must have the switch to know the position for proper shifting. It will likely turn Out to be a cluster issue if this is the case.
If you are having shift issues such as range shift inhibited , it will be wiring, the pressure switch manifold inside the pan or the transmission module.
Please have a look and let me know which so we can expand on it Jason.
Customer: replied 2 years ago.

It does seem to shift fine, occasionally it hits real hard coming out of park, throws general 0700 code then i have to clear it out to get moving again . Since last night it did it again and now no reverse lights .when I first cycle key the trans temp gauge jumps up and immediately drops back to zero

Customer: replied 2 years ago.

And now going into drve takes several tries...

Expert:  Gm Tech Cam replied 2 years ago.
Ok so it's a wiring or module issue. If you wiggle the round connector on the back passengers side of the transmission, does that change it? Is there tension on that connector pushing it sideways?
Customer: replied 2 years ago.

No change , I moved it around while someone inside watching dash

Expert:  Gm Tech Cam replied 2 years ago.
Ok, let's try unplugging that carefully and check the wiring between that connector and the transmission module. Check closely beside the power steering pump.
Customer: replied 2 years ago.

I pulled the trans harness out and disconnected the tcm so I could ring out each wire end to end , the only thing I've found is the light green wire(f) and the black with white stripe (d) on the gray nsbu connector both ring when cconnected in number 1 terminal on "gray" tcm connector

Expert:  Gm Tech Cam replied 2 years ago.
When you say ring, are you checking continuity? Resistance?
Customer: replied 2 years ago.

Continuity, just put all back together no change . Drl's are still on , reverse lights still off , no trans temp or gear indicator

Expert:  Gm Tech Cam replied 2 years ago.
The F and D, were those on the NS BU or into the round connector?
Customer: replied 2 years ago.

Nsbu

Expert:  Gm Tech Cam replied 2 years ago.
OK, I made some headway. That light green wire, that is supposed to have power in reverse from the NS BU. So if you apply power to that it should make the back up lights come on.
So if it does not get power then lets see if the pink wire gets power. IT should with the key on. If no then the B/U LP fuse in the underhood fuse block may be bad.
For the temp signal, test the resistance with a meter from the yellow black at the red TCM connector to the black wire also in the Red connector. Let me know what the resistance is.
Customer: replied 2 years ago.

I'll give it a try tomorrow afternoon I just put it together and heading home from the shop appreciate your help

Expert:  Gm Tech Cam replied 2 years ago.
No problem. I hope to be able to reply quicker tomorrow. I got stuck with a timing chain job that I did not start, so got busy
Customer: replied 2 years ago.

I understand , I'm a welder and small jobs always seem to snow ball , the hour different time zones are a challenge too

Expert:  Gm Tech Cam replied 2 years ago.
That does not help, no. But tomorrow will be better.