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ABKirsch, ASE Certified Technician
Category: Car
Satisfied Customers: 13
Experience:  I hold 6 ASE Certifications and have 6 years of professional automotive experience.
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GM: ton..duramax..first gear..Tried shifting through the gears.P,D,N

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My 2002 3/4 ton GM HD 2500 w/duramax engine and allison transmission does not shift out of first gear. Tried shifting through the gears.P,D,N,3,2,1 nothing. stuck in first.Truck has been taken care of, good @ 99,900 miles until now!

Hi Brad,


I checked for technical service bullitens and did not find any on this concern. Every time I've seen or heard of this transmission stuck in first with full fluid it has required overhaul due to internal parts failure. Even if you've had the service performed every 25K this can still occur. Transmission failure is not always a lack of maintenance. If you have a malfunction indicator light on in your cluster, and you have a scanner readily available you can check for codes (even if the light is not illuminated, you can still check for codes, and even if they are history codes they may be helpful in diagnosis). If you have an advanced scanner with the right software, you may be able to perform a more detailed electronic diagnosis, but since you didn't mention having access to GM or Allison tools and software, I assume you are trying to perform mechanical diagnosis first. Assuming you have access to none of the tools to check the transmission electrical system or pressures, you can still look at a few helpful things to start. Check not just the level of the fluid, but the color, odor and contents. Specifically you should prepare as if to do a transmission service, but when you drain the fluid drain it into something where you can inspect it. Check the fluid for a burned odor and a black or dark brown appearance. Also check the filter, fluid and pan magnet for metal chunks or excessive metal shavings. If you have already tried these suggestions, let us know what you found. It is important to have this information to know what to do next. It is also important to know how much equipment you have access to and whether or not you feel able to rebuild or replace the transmission if necessary.

Customer: replied 8 years ago.
The truck took a pretty violent hit to the front driver's side wheel ( no damage) when it (I) hit a snow covered curb, after that the electronic display for the gear selector no longer had an accurate readout, when the truck was in drive the readout read it was in third gear, also the door locks before the hit would open when the truck was turned off, this is no longer the case. Is the automatic transmission dependant on the computer system? The transmission had shown no signs of trouble before this hit to the drivers side. Could this jarring hit be a cause of the transmission not shifting out of first gear?

Actually just between those two systems you have involvement of the transmission, engine, powertrain and body control modules. Since different modules control the systems, and both issues started at the same time, the computers aren't the greatest starting point, though. One thing I did notice in looking through the wiring diagrams, is that the shift lever is next to the ignition switch and the ignition switch is what sends the signal to the door lock actuators to lock the doors. Both are in the steering column, and your vehicle uses a shift cable to the transmission to actually shift. You said there is no damage, but do you mean body or mechanical damage by that? Since you took a major hit to the left front wheel, have you should inspect the hub bearing and the steering linkage. Your steering gear attaches to the frame on left side as well and the intermediate steering shaft is also there, leading to the column, where the two systems you are having issues with come together. If you haven't already, you should inspect the steering system and frame on the left side for damage, along with the bearings, ball joints and front axle and differential if you have a 4x4 both for this problem, safety while driving and financially if you find there is extensive mechanical or frame damage you might want to consider making an insurance claim if you have collision coverage. While you are under there, you can see if there is anything bent blocking normal operation of the shift cable or if it is damaged. You'll have an easier time at this than disassembilng the column to inspect the shift cable and ignition switch wiring, but if you don't see anything underneath that's the next place to look. The shift cable runs from the lever inside the column down the column and attaches at a lever on the transmission. Let me know what you find.

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