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Allison help!!!!!

Discussion in 'Chevy Trucks' started by 86CrewcabK30, Feb 20, 2007.

  1. 86CrewcabK30

    86CrewcabK30 Junior Member
    from iowa
    Messages: 21

    I have an '02 2500HD with the 8.1/Allison combination. About a month ago I started having problems with what I thought was the NSBU switch from everything I had read. The problem was intermittent, on dry days it worked fine, on wet days it would act up. I would have park, neutral, and 3rd gear only in wet conditions. I finally had enough when the last time my check engine light came on with it. I went to my local dealer and bought a new NSBU and installed it and it made no difference. I was wondering if anyone else had run into this situation or if the NSBU switch I got may be defective off the shelf? Could it be the harness or the transmission ECM ($$$)? It has been a great truck so far. I just want to get an idea of what this may cost before I get it to the dealer. Sure glad I still have the '86 tonner for backup! Thanks in advance for your help!
     
  2. lawnmedic

    lawnmedic Senior Member
    Messages: 703

    Did you get the computer read and flashed. No reason to throw parts at a problem if the computer can tell you whats wrong....
     
  3. 86CrewcabK30

    86CrewcabK30 Junior Member
    from iowa
    Messages: 21

    I haven't yet. I just wondered if there was anything I could do before taking it in. Thanks!
     
  4. snyps

    snyps Senior Member
    Messages: 101

    Are any of the gear indicators flashing. Mine was doing the same thing but the indicator was flashing when it happned. Also bring it to a local parts store they should be able to run the codes for you for free and see what you get. I googled the codes and say a ton about that switch being the problem.

    Also to have that switch put in there is a new style that requires a tech 2 programmer hooked up and something to be done to the computer. Not sure if it is just clearing the codes or something else.

    Good Luck
     
  5. 86CrewcabK30

    86CrewcabK30 Junior Member
    from iowa
    Messages: 21

    Snyps the Park indicator comes on when I start it and then the check engine light comes on. Nothing other than that. The switch I put on is the updated tan switch. Do I have to have it programmed after installing the new switch? Thanks for the reply!
     
  6. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    No, it's not nessesary to reprogram the switch after a replacement. Are you sure you installed the switch correctly? Did you have any trouble sliding it over the shift shaft sticking out of the trans case? When you take the switch out of the box it should have had a plastic holder tool on it to hold the switch in the Neutral position,so the trans need's to be in Neutral too in order to install the switch.Since your check engine light is on you should definitely have the TCM (transmission control module) scanned for code's as their's gonna be one or more stored codes in it. Also, on an Allison trans, when you only have a limited number of gear position's like reverse and 3rd, this mean's that the TCM has discovered a problem and it put's the trans into "limp mode" in order to protect itself. Without a doubt, the next step you should take is getting it scanned.
     
  7. 86CrewcabK30

    86CrewcabK30 Junior Member
    from iowa
    Messages: 21

    Thanks for the information. I scheduled it in for 7AM tomorrow morning to be looked at. I will post what they find. I followed the installation instructions to the letter. Had the neutral assurance bracket on it and checked it during installation. It did go on the shaft tightly, so I lightly sanded the crud off the shaft until it went on without alot of force. I don't think I damaged the switch. The electrical connectors were tough to get out of the old one, but the terminals looked good when I got them off. I guess I will find out for sure tomorrow.
     
  8. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Sounds like you did the install correctly, so more than likely they wont find any problems with the switch. Your old switch is probably ok too so you might want to hang on to it for a spare.Keep us posted on what they find.:)
     
  9. Turf Masters

    Turf Masters Member
    Messages: 93

    Have the same problem!

    Had the same problem last storm 2/14.There was a recall from 02-05 for the trans module.I have 2 06's and both had to have new transmission modules installed on the Allison.No problem when its dry,only in wet conditions.

    Glenn.
     
  10. snyps

    snyps Senior Member
    Messages: 101

    This information:

    A flashing PRNDL display may be the result of incorrect sensor inputs or transmission abuse protection modes being received by the TCM. The following are some of these conditions.

    • The transfer case is/was in Neutral.
    • The transfer case is/was shifted into Neutral when the vehicle is moving.
    • A decrease of the input turbine speed was not detected when the gear selector was moved into any gear.
    • A low transmission fluid Level.
    • A misadjusted PNP/NSBU switch.
    • Turbine input speed or output speed sensor failure.
    • Failures of the shift solenoids to route the transmission oil to the proper clutch assemblies within the transmission.
    • Failures of the transmission clutch packs (C1 or C5 for first gear, C3 or C5 for Reverse).
    • Failure to detect proper line pressures when a gear range is selected, which may be the result of normal maintenance such as a transmission fluid change having been completed, or the transmission pan was removed for a filter replacement or other type service.

    is from this link www.diesel-central.com/Tech/GM-TSB/Service Bulletin.doc it states that you have to re flash computer not the switch. It might be necessary and in my case it was for the new switch to work correctly.

    I hope this helps, good luck!
     
  11. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    I've never had to reflash a TCM after changing the NSBU switch. The TCM should only need reprogrammed after changing the TCM itself or changing any of the internal solenoids. What was the deal on your truck synps? Why did they reprogram it? Are you sure they didn't just do a "Fastlearn" (GM lingo) procedure?
     
  12. StathemLawncare

    StathemLawncare Member
    Messages: 37

    I have an 03 Duramax with allison. Same problem as your having.It is the range shift piece on the driverside of transmission. there are to electric plugs on it. Mine was cracked.Check engine light came on but went off after a couple days.It is very easy to fix yourself. Took about one hour.I think it was around $180 for the part.
     
  13. snyps

    snyps Senior Member
    Messages: 101

    I had to drive the truck with it like that for about 50 miles before it was fixed. I just know I put the part on and it didn't fix the issue until they hooked it up to the tech2. These trucks are just way to smart sometimes. The bad part was I was in 4lo when it happened during our October storm and it wouldn't shift out for about an hour.. I was just stuck at the end of the driveway fing with it until I could get it into 4hi so I could get out of there.

    The tech service bulletin says to do it, so there has to be some reason why. I don't see those being wrong very often. I bet it has something to do with the pressures in the tranny being off and having to clear codes and such, but I am not a GM tech so I am not sure.

    I guess more information the better. But just for the sake of people that read this down the road that haven't had the problem and just came by this on a search, if you can wait a day or two for the part you can get it online for about $70!!!
     
  14. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    I'd say they just used the Tech 2 to clear the previous codes to allow the trans to relearn the shift characteristics. If you just replace the switch and don't clear the TCM of codes, the Allison's can/will stay in limp mode no matter how long you drive it as the TCM won't clear the codes by itself after the problem is fixed like an engine ECM will, after the truck goes through 40 ignition on/off cycles.
     
  15. 86CrewcabK30

    86CrewcabK30 Junior Member
    from iowa
    Messages: 21

    $300 and two broken wires spliced and she's as good as new. Not counting the $140 NSBU switch.Thanks for all the help! I hope this helps somebody else down the line.
     
  16. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Do they think you damaged the wires or was that the problem before you even changed the switch?
     
  17. 86CrewcabK30

    86CrewcabK30 Junior Member
    from iowa
    Messages: 21

    I think they were broken before I installed the switch. What I find odd though, is that the problem was intermittent for a while, and only seemed to happen initially when I was in wet conditions or deep snow, making me think it was the switch. Maybe the moisture was getting into the breaks in the insulation and not the switch and then the wires broke completely before I changed out the switch (thus the service engine soon light coming on). I was very careful when changing the switch. It did need the updated switch anyway I guess?
     
  18. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    An intermittent problem when dealing with damaged wires isn't uncommon at all.They'll do some weird things when the control system doesn't get the correct signal at the correct time.Since you replaced the switch with the updated version, I'd say the money you spent on the new switch was well spent.