Allison Trouble Codes

Discussion in 'General RVing' started by HalC, May 24, 2006.

  1. HalC

    HalC New Member

    I have a 2001 2500HD Silverado with 8.1 litre engine and Allison transmission with 25K on it. The transmission was serviced in October and found to be as good as new. I pull a 25 foot trailer with no strain. During my last outing I had stopped for awhile and when leaving the transmission would not come out of third and the service engine light was on. I stopped, turned the engine off and when starting again the transmission shifted normally. Coming home after driving 125 miles which included two steep climbs the engine light came on a few blocks from home and the transmission would not shift out of low when the light changed. I stopped a block up at the next light, turned the engine off and when I started again it would not come out of neutral. I turned it off, waited and started it up. The engine light was now off and the truck shifted like normal.
    Once the trailer was disconnected the transmission performed just like new. The codes found later were PO700-Trnasmission Control System Malfunction and PO778 Pressure Control Solenoid B Malfunction.
    I bought a Chilton book but these codes were not listed. It has only happened when the trailer was connected and when it corrects it works perfectly. Can this be related to any electrical feedback from my trailer? Or should I just go ahead and replace the Solenoid? Is it internal or external to the transmission. Do solenoid have intermitten problems?

    Thanks in advance for any advice you may have.
     
  2. camper85

    camper85 New Member

    Allison Trouble Codes

    We have the same truck only a year newer and have had no problems...we tow a fifthwheel. What did your dealer say? You know you can place a call to Chevolet and they are usually pretty good about helping out with problems. I dont have an answer of why it could be doing this unless it is something with the trailer brakes.
     
  3. HalC

    HalC New Member

    Allison Trouble Codes

    The trouble light came on once again while not towing the trailer. It started declining to shift out of low gear unless I shut it off for a while. While this appears to be a once in a while problem I'm taking it in tommorrow morning to have the shifting solenoid changed. This will hopefully close this topic.
     
  4. llabbott77

    llabbott77 New Member

    Allison Trouble Codes

    I have the same truck as you but I have 270,000 miles on the odometer. Twice now I have had to replace the shift sensor, after exhibiting the same symptons. I understand that the sensor is located on the outside of the transmission. The cost has been around $100.00. I recommend seeing your Chevy dealer as soon as possible when the check engine light comes on with the vortec engine. Great truck isn't it! Good Luck.
     
  5. AdamBlattel

    AdamBlattel New Member

    Allison Trouble Codes

    I have read alot about Allison's getting into "limp" mode, which is basically when your trans is getting hot, or being ran too hard...It put's itself into a mode in which the trans wont goto OD and it almost seems as the truck wont go into first either...This might be what your running into....

    I just purchased a 02 with a duramax/allison...and it is chugging when in first gear right before stopping at stoplights... And this is without a trailer behind it. We have a trip coming up in 4 daqys to michigan, and I hope nothing somes of it...

    Anyone heard of this???


    Adam
     
  6. AdamBlattel

    AdamBlattel New Member

    Allison Trouble Codes

    I have read alot about Allison's getting into "limp" mode, which is basically when your trans is getting hot, or being ran too hard...It put's itself into a mode in which the trans wont goto OD and it almost seems as the truck wont go into first either...This might be what your running into....

    I just purchased a 02 with a duramax/allison...and it is chugging when in first gear right before stopping at stoplights... And this is without a trailer behind it. We have a trip coming up in 4 daqys to michigan, and I hope nothing somes of it...

    Anyone heard of this???


    Adam
     
  7. dbarton291

    dbarton291 Senior Member

    Re: Allison Trouble Codes

    The shift sensor you're referring to is the NSBU switch on the side of the trans. Neutral start backup switch. They do go bad sometimes. You can head over to www.allisontransmission.com and buy the real mccoy service manual and troubleshooting manuals. You can't run an Allison too hard and put it in limp home mode.
     

Share This Page