# Need help reverse messed up 02 chev 2500HD



## nrplowguy (Apr 15, 2008)

I have a 2002 Chevy 2500HD with the duramax with the Allison 1000. My truck started not having reverse. When I start it, it is fine but about 10 seconds in or so it will pop out and it will never go back in. I can then shut of the truck wait about 5 seconds or so start it up and it will go right in then pop out 10 sec later(sucks when doing tight non drive threw driveways). I was due for a transmission service thought that was the cause no avail. I was told that it might be my neutral start backup switch I can now start it in neutral now but no help on the reverse. I talked to someone at Allison he has worked there for like 8 years and he said he has yet to hear something like this with no symptoms before hand. ANYONE PLEASE HELP would like to get some idea of what it could be so when I bring it in I can know what to expect……..


Chubb


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## ponderosa (Jan 8, 2006)

i had the same problem this winter on a 2001 chevy with a allison we put in a new neutral safety switch all better good luck


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## B&B (Nov 4, 2006)

Yes, sounds like the classic symptoms of a NSBU switch. $60-$80 from the Allison dealer. 20 minutes to swap out. Also check the trans harness as it snakes down toward the trans. Some 01-02's were improperly routed and rubbed through the sheathing and into the wiring harness.


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## nrplowguy (Apr 15, 2008)

i replaced the nsbu switch to no avail. Where about were the trouble spots on the harness so i can pin point it if you guys know where abouts they might be


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## B&B (Nov 4, 2006)

If you follow the wiring from the trans up the truck you can check it for any chaffed spots. They like to rub through near the rear of the engine. Also check the ground wire on the frame. located directly below the driver side rocker panel. Make sure they're clean and tight.

Few questions Chubb:

Who did you purchase the switch from? Genuine Allison/GM is what you want.

Are you sure the NSBU switch is properly adjusted? Did you follow the correct change procedure?

Does your shift indicator on the dash display properly/correctly? Have you even had a "shift range inhibit" message in the display, or has the shift indicator ever blinked on and off.

Has the check engine light come on due to this problem? (have you had it scanned for trans codes?)

Make sure the fluid level is correct. The Allisons can be very temperamental in relation to fluid level.

The 01-02's also had problems with the trans losing pump prime...but usually only did that after an extended period of non use (over night).


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## nrplowguy (Apr 15, 2008)

yes i my NSBU switch is an Allison one and i marked it before i put it on so it would be correct. my reverse light when it is acting up will blink on and off and when it is blinking i have delayed engagement going from reverse to drive and also to park. when i put it into park from reverse i can hear a loud click from the tranny right under the drivers seat. My SES light is on and my friend scanned it and it said that it was tourqe converter electrical and tourqe converter electrical stuck on. levels are good. i will try and take a look at my wiring and see what i can come up with. i got warranty left but all the dealers around me are beings jerks and wont look at it without any money down well i just got back to work so not much money inflow..............


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## B&B (Nov 4, 2006)

nrplowguy;552812 said:


> when i put it into park from reverse i can hear a loud click from the tranny right under the drivers seat.


 Thats completely normal for the Allisons, it's the parking pawl engaging when park is selected. If you've ever seen the size of the park pawl in an Allison in comparison to other transmissions it'd be clear why you can hear it engage with a very solid audible "clunk". Very massive indeed.

Sounds like you've got the basics covered. I'd also clear the codes if you haven't already done so. Very important on the Allisons after performing a repair. Check over the wiring with a fine tooth comb and be sure to check the grounds, and especially the battery terminals as well.


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## nrplowguy (Apr 15, 2008)

Ok Thanks i will see what i a can do and will let you all know what it is so you guys can possibly pass it on to others


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## Yaz (Apr 13, 2005)

See if your mechanic can read codes from the TCM and ECM. If you have all forward ranges with no reverse and you have a good NSB and no shorts, bad grounds etc I suspect the F solenoid may be the problem in the trany. I read they had a problem with them during 02 model year. A code check will help diagnose it.


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## nrplowguy (Apr 15, 2008)

*got it figured out*

well I brought it in and they told me it was the TCC solenoid and the internal wiring harness at the same time my injector decided to go out well with 200 miles left on warranty it had good timing


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