Jump to content

Allison Tranny Issue/question On 01 Hd 2500

MTIrish98

Recommended Posts

MTIrish98 New Member

MTIrish98

Posted
Posted

Gentlemen,

 

I recently purchased a used 2001 HD 2500 Sierra with about 59K miles on it. I really like the truck, but I may be experiencing one of the problems I read about before I bought it.

 

I have the 8.1L gas engine w/Allison Tranny. I had read of a problem specific to '01s where the tranny isn't always in the gear the automatic gear selector says it is in. Once I was in 'D' but going down the highway at 3500 rpms. The second time I couldn't find reverse at all. In both cases shutting the truck completely off and then restarting made the problem go away.

 

Is this a programming issue? I appreciate any tips or ideas! It doesn't seem like a big deal now, but I can imagine some bad places not be able to find reverse during hunting season.

ss502gmc Enthusiast

ss502gmc

Posted
Posted

Welcome!! Yup it sounds like youll need to join the club of having to get a new NSBU switch installed. It should be ok for a little while but once it starts acting up on a regular you eventually wont be able to drive it anymore. If it hasnt done it already you will experience the tranny shifting itself into 3rd gear on its own "fail safe gear" and a screwed up prn321 display. Its a pretty simple fix, i installed one on my truck in about 30 min. The part was a genuine Allison part and cost about 200$. Goodluck!!!

MTIrish98 New Member

MTIrish98

Posted
  • Author
Posted
Welcome!! Yup it sounds like youll need to join the club of having to get a new NSBU switch installed. It should be ok for a little while but once it starts acting up on a regular you eventually wont be able to drive it anymore. If it hasnt done it already you will experience the tranny shifting itself into 3rd gear on its own "fail safe gear" and a screwed up prn321 display. Its a pretty simple fix, i installed one on my truck in about 30 min. The part was a genuine Allison part and cost about 200$. Goodluck!!!

 

By simple do you mean simple for a GMC Enthusiast, or simple for a guy who can work his way around a lawn mower engine?!?

 

I do get the screwed up PRN321 display occasionally now.

ss502gmc Enthusiast

ss502gmc

Posted
Posted

It really is pretty simple. The switch is mounted on the drivers side of the tranny and its where ur shift cable mounts to so theres a couple mounting screws that hold it to the tranny and a nut that holds the shift cable to the switch but the most important thing is to make sure when you install the new one you must make sure the shift cable is in the same position as the old switch but if you buy the allison genuine part it comes with a line up clip so you dont screw it up but also before mounting the new one u may have to sand/file the burr on the shaft so that it doest scrape the inside of the new switch. the hardest part i had was getting the new one on without forcing it because of that burr but my first time was only 30-40 min. Goodluck!!

spackelman Enthusiast

spackelman

Posted
Posted
It really is pretty simple. The switch is mounted on the drivers side of the tranny and its where ur shift cable mounts to so theres a couple mounting screws that hold it to the tranny and a nut that holds the shift cable to the switch but the most important thing is to make sure when you install the new one you must make sure the shift cable is in the same position as the old switch but if you buy the allison genuine part it comes with a line up clip so you dont screw it up but also before mounting the new one u may have to sand/file the burr on the shaft so that it doest scrape the inside of the new switch. the hardest part i had was getting the new one on without forcing it because of that burr but my first time was only 30-40 min. Goodluck!!

 

 

The hardest part for me was getting the wire harnesses off the old switch. Overall though, took about an hour.

ss502gmc Enthusiast

ss502gmc

Posted
Posted

Do a google search and youll find some step by step instructions on replacing the switch.

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • asilverblazer
      2027 GMC Sierra: Official Discussion

      By asilverblazer · Posted

      Kudos? Are any of them desirable? Class leading (in any metric)?
    • GMCustomerService
      2026 TurboMax L3B 2.7L: AFM/DFM present/disablable? [2026 Silverado 1500WT: 4WD RC RB 2.7L]3GCNKAEK9TG345558

      By GMCustomerService · Posted

      Those are great questions, Bill. Our team looked into your VIN and it doesn't appear to have AFM or DFM. Please know, we take the personal and private information of our customers seriously, and we don't recommend posting your full VIN publicly. As for Auto Stop, some vehicles have a button to turn Stop/Start off for one ignition cycle. If the vehicle is equipped with the Stop/Start deactivation switch, you can push the switch to turn off Stop/Start. Stop/Start is turned off when the LED indicator on the switch is not illuminated. If you have any further questions, please visit https://s.chevy.com/support-request and fill out the support request form with all pertinent details. This form helps our team gather the right information and ensures your request is routed appropriately. 
    • diyer2
      The Peckish Synapse

      By diyer2 · Posted

      She's laughing all the way to the bank.
    • newdude
      SLE 2.7L L4 shudders @ 2000-3000RPM

      By newdude · Posted

      There's a new PI on 2023-2026 L3B shudder.  Possible faulty front oxygen sensor.   Dealer can pull up PIP6060A and give it a read.  
    • newdude
      OBD not ready?

      By newdude · Posted

      Also here's the drive cycle for a 2021 Yukon with V8.  DO NOT USE THE CRUISE CONTROL WHEN RUNNING DRIVE CYCLE!!!!!:   Warning: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage. Note: You have completed this procedure when all parameters display Complete. Short stops for traffic will not affect the procedure. Note: Do NOT use cruise control during this procedure. Ignition/Vehicle » Off — For greater than 8 h Verify the scan tool parameter: Cold Start-Up = Yes If not the specified state Ignition/Vehicle » Off — For greater than 8 h & Repeat this step If the specified state Ignition » On / Vehicle » In Service Mode — For 1 min Engine » Idling — For 2 min Drive the vehicle while maintaining the following conditions for 20 min: Part Throttle Vehicle Speed = 24 to 97 km/h (15 to 60 MPH) Safely stop the vehicle Operate the engine/vehicle within the following conditions: Accelerate the vehicle to 64 km/h (40 MPH) Accelerate the vehicle from 64 to 97 km/h (40 to 60 MPH) @ Throttle position between 10% and 13% Release the accelerator pedal and let the vehicle coast down with the brake pedal released — For greater than 20 s Accelerate the vehicle from 64 to 97 km/h (40 to 60 MPH) @ Throttle position between 13% and 16% Release the accelerator pedal and let the vehicle coast down with the brake pedal released — For greater than 20 s Accelerate the vehicle from 64 to 97 km/h (40 to 60 MPH) @ Throttle position between 16% and 19% Release the accelerator pedal and let the vehicle coast down with the brake pedal released — For greater than 20 s Accelerate the vehicle from 64 to 97 km/h (40 to 60 MPH) @ Throttle position between 19% and 22% Release the accelerator pedal and let the vehicle coast down with the brake pedal released — For greater than 20 s Accelerate the vehicle from 64 to 97 km/h (40 to 60 MPH) @ Throttle position between 22% and 25% Release the accelerator pedal and let the vehicle coast down with the brake pedal released — For greater than 20 s Maintain steady state throttle at 89 km/h (55 MPH) — For 10 min Safely stop the vehicle

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...