2002 Chevy Duramax 2500 with Allison - tranny problems

DriveHard

DriveHard

Joined
Nov 24, 2003
Messages
3,783
Location
Middle of Iowa
My BIL has the subject truck that has now been parked for three weeks in my front yard...he is a "throw parts at it" kind of guy, and doesn't have a ton of money. Any thoughts on this would be appreciated.

Limped it into my driveway a little over three weeks ago
Service ABS and Service 4x4 messages on the dash
4x4 selection lights do no light up
won't stay in D or R - you put it in gear, and it will drive about 20 feet, and pop right back out of gear into neutral
No DTC's that I can see with a standard scanner
fluid is full and clean

I cleaned the grounds under the driver door, as I have read that is a common problem - no change
inspected wiring looking for loose/chewed wires and found nothing
My BIL replaced the TCM with a brand new one flashed to his VIN with no change - he now wants to replace the ECM (dumb IMHO).

I have heard of a tranny going into limp mode and limiting speed/shifting - but since you are mechanically shifting the spool, wouldn't it at least stay in gear? It seems odd that it will come out of reverse or even 1st gear.

Any thoughts/opinions would be greatly appreciated.
 
Get a scanner that reads more than standard codes, and work from there. There are obviously reasons the Service ABS and Service 4x4 lights are on... Throwing the parts cannon on it won't solve it faster...
 
MNgopher said:
Get a scanner that reads more than standard codes, and work from there. There are obviously reasons the Service ABS and Service 4x4 lights are on... Throwing the parts cannon on it won't solve it faster...
Click to expand...

Yes, I know...thank you. That is why I was asking here to see if there was any trouble shooting that could be done without the expensive scanner. It is not my truck, and I don't need an expensive scanner at this point, and my BIL won't pony up to get one as he is most likely going to sell it after he gets it going again. If you would like to drive down and scan it for free...it would be much appreciated!
 
The errors/problems seem very similar to a common problem with the Neutral Safety Backup Switch...any thoughts?
 
DriveHard said:
Yes, I know...thank you. That is why I was asking here to see if there was any trouble shooting that could be done without the expensive scanner. It is not my truck, and I don't need an expensive scanner at this point, and my BIL won't pony up to get one as he is most likely going to sell it after he gets it going again. If you would like to drive down and scan it for free...it would be much appreciated!
Click to expand...

You did ask for any and all help. Not just the answers you wanted (and didn't specify in the original post). The usual diagnostic tree would be to pull the detailed codes to focus your effort. The P0700 is literally just an indication that there is more detailed diagnostic info available. But hey, have at it...

Between some cheap OBD II adaptors, and phone and computer apps (like Forscan), I can see all the detailed codes it cost me less than $50... But then again, that's for my Fords and may not apply to GM.

Good luck with your repair.
 
A P0700 in the PCM only indicates DTC's are stored in the TCM, You need a capable scan tool to scan the TCM.
P0500 indicates that no VSS signal is received from the TCM.

*Does the Speedometer operate properly?
*I'd just about insist on scanning the TCM, BUT.....It's possible that the TCM is just throwing redundant P0721/P0722 VSS Sensor codes?? If so, The wiring between the VSS & TCM, The VSS Sensor, And the Transfer Case being so worn out that the VSS Reluctor Wheel is hitting the Sensor are possible causes.
*Is there fluid in the T-case & what condition is it in?

***Neutral Safety Switch issues generally cause the Gear Indicator Display to display the wrong shifter position or no position at all
 
clinebarger said:
A P0700 in the PCM only indicates DTC's are stored in the TCM, You need a capable scan tool to scan the TCM.
P0500 indicates that no VSS signal is received from the TCM.

*Does the Speedometer operate properly?
*I'd just about insist on scanning the TCM, BUT.....It's possible that the TCM is just throwing redundant P0721/P0722 VSS Sensor codes?? If so, The wiring between the VSS & TCM, The VSS Sensor, And the Transfer Case being so worn out that the VSS Reluctor Wheel is hitting the Sensor are possible causes.
*Is there fluid in the T-case & what condition is it in?

***Neutral Safety Switch issues generally cause the Gear Indicator Display to display the wrong shifter position or no position at all
Click to expand...

Clinebarger, thanks again for the help!

No, the speedometer does not work, and there is not gear indicator as well. I'll see if I can pop out sometime today and check the fluid level in the T-case.

Do you have any suggestions on a cost effective way to scan the tranny codes? I also own a Chevy truck, so if it is something I could use in the future, I would be willing to make a small investment to help my BIL.
 
Was the gear indicator display working before the issues? The display itself can go out & not cause any driveability concerns!

I use a GM Tech 2, Snap-on Solus, & HP Tuners for GM vehicles, HP is the cheapest at $300. Don't have any experience with other scan tools. I'm sure there is some cheap Tech 2WIN software.
 
You must log in or register to reply here.

Similar threads

92saturnsl2
2020 Silverado 3500 - Limp mode, trailer issue or not?
Replies
3
Views
662
weaponoffreedom
J
Ford ranger transmission shifts too soon
Replies
12
Views
1K
dogememe
1 SX
Sonata 2.4L P1326 limp mode/flashing check engine light/1800 rpm limit
Replies
19
Views
10K
1 SX
U
GM transmission control module 2425 6861 update
Replies
1
Views
317
bdcardinal
M
4T65E in 2006 Buick Lacrosse CX 3.8L, 2nd gear starts
Replies
18
Views
2K
zrxkawboy
Back
Top