2001 - 2004.5 Allison 1000 Trouble Shooting

The Allison 1000 5 Speed transmission came in 2001 - 2004.5 heavy duty Chevy and GMC trucks. At the time it came out it was cutting edge. Smoother shifting and more robust than almost any other transmission that came from the factory. DT750 pre built transmission duramax

However, they do have a reputation for having issues once power and abuse have been added to the truck. Most commonly they go into "Limp Mode" during the 4 to 5 upshift or 5 to 4 downshift under hard acceleration. This will cause a check engine light to come up on your dash and the truck to be limited by power and speed. When this happens the most reported code is P0700. GM defines PO700 as Transmission Control Module Requested MIL Illumination. Simply said, it's a general code for transmission issues and generally is accompanied by another code such as P0701, P0702, and so on.

Many truck owners' first reaction is to replace the Transmission Control Module (TCM) as soon as this code pops up. The reality is further diagnosis is needed to tell what the issue is and the best way to resolve it. Never jump to conclusions and always take into consideration the circumstances behind the issue prior to the code coming up.

Where can you learn more about P0700 codes in your Duramax?

Diagnosing 5 Speed Allison 1000 Transmission Problems:

This is not meant to be a complete tutorial on building transmissions but rather a point of reference when diagnosing your own truck. It is always a good idea to have a certified professional with experience inspect your truck prior to making a final diagnostic. Or you can request an estimate through the button below.

Step 1: Read Codes

Always start by reading all of the codes triggering the check engine light. This is the best way to narrow down the root cause of the issue. P0700 is a general transmission code most commonly accompanied by another P-code (P07xx, P0218, ect). Anyone capable of helping will require this information to move forward.

Step 2: Back Story

"I was driving down the highway with the cruise on" is the most common story, but probably not the most honest. "Lightly rolled on it" is very different than "Went wide-open throttle from 35 MPH until the speedo tapped out". The more honest you are, the better help you will get. For the 5 Speed Allison, a weak point is the 4-5 upshift and the 5-4 downshift. That being said, try to keep in mind that reasonable driving and conservative tuning can keep you safe.

Step 3: Driveability Symptoms

Details! Details! Details! This is how to help yourself. The more details you can gather about how the truck is driving now, how it shifts, at what speed, noises and from where, how many RPM and anything else you can track that is related to the issue. You and anyone helping may not need every detail you track, but it is better to have the data and not need than need the data and not have it.

Step 4: External Inspection

Start by checking the transmission fluid dipstick. Does the fluid look or smell burnt? Next, are you leaking transmission fluid anywhere? Change your external filter if you have not recently changed it. When you drop it down check the magnet on top of the filter for any debris or material. Is there any chattering noise in reverse or drive? Does it clunk really hard when you put it in gear?

Step 5: Common Issues

Having some idea of possible issues can help you hone in on the problem. Use this list as a reference for the most common root causes of the 5 speed Allison failure.

Burnt Clutches
Twisted P2 Planet
Torque Converter Chatter
Bad solenoid
Debris blockage in the valve body
Improper C3 lubrication
Electrical issues / bad

Again, this is a great place to start diagnosing your P0700 codes for 2001-2004.5 (LB7 & LLY) Allison-equipped HD trucks. However, final diagnostics should always be done in person by a professional.

If you are diagnosed your transmission to have failed mechanically or if you are ready to put more power on the ground, the DT750 from DuramaxTuner.com may be right for you.