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Allison throwing 30 codes and pulling odd

Landon730

Landon730

Active Member
Messages
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Location
Greenwood Arkansas
I've got an 02 duramax and I'm having a strange problem with it. You clear the codes and it pulls in reverse just fine, but put it in drive and you cant go but 5 feet without it quit pulling and turning on the SEL light. First codes I got off it pointed at the NSBU switch. Dropped $200 on it today, problem persists. Broke down and bought a good scanner that reads individual modules and I have 30 codes. Mainly low voltage codes. I unplugged the round plug from the trans and it poured out ATF. I cleaned both ends with break clean just to see what it would do. Pulled for the longest amount of time after that but the problem persists. As soon as the codes are cleared they come right back. Ideas?
 
With that many codes I always write them all down. Then clear them and try to drive it to see what returns. Then diagnose what comes back first.

Low voltage and/or u codes may indicate a power supply or wiring issue. Also the TCM need to see input form the speed and pressure sensors. I would diag any voltage codes first, then go after and sensor codes that may have set.

Give us a list of what codes it set. So one of us can lead you to the correct repair.
 
Rockabillyrat said:
With that many codes I always write them all down. Then clear them and try to drive it to see what returns. Then diagnose what comes back first.

Low voltage and/or u codes may indicate a power supply or wiring issue. Also the TCM need to see input form the speed and pressure sensors. I would diag any voltage codes first, then go after and sensor codes that may have set.

Give us a list of what codes it set. So one of us can lead you to the correct repair.
Click to expand...
I’m down to 0842, 0847, and 0872
 
Those codes are for the pressure switches. You need to monitor your pressure switches with the scan tool and see if they are switching when they should be. The codes sets if it sees the switch close when it should be open. TCM commands a solenoid and uses the pressure switch to confirm physical movement in the valve body. So if it commands a solenoid it should see a change from the pressure switch. It could be a bad wire, pressure manifold switches, or even a stuck valve in the valve body.
 
Last edited:
Rockabillyrat said:
Those codes are for the pressure switches. You need to monitor your pressure switches with the scan tool and see if they are switching when they should be. The codes sets if it sees the switch close when it should be open. TCM commands a solenoid and uses the pressure switch to confirm physical movement in the valve body. So if it commands a solenoid it should see a change from the pressure switch. It could be a bad wire, pressure manifold switches, or even a stuck valve in the valve body.
Click to expand...
So basically need to take the pan off, clean the valve body and solenoids, and check the wiring?
 
THEFERMANATOR said:
How is the fluid level? When you get multiple pressure switch codes like that you want to check the fluid level 1st. A torn filter seal can also cause issues like this.
Click to expand...
Well i pulled the pan off and my fluid is literally the color of double bubble bubble gum. TONS of sludge in the pan and on top of the filter. I’m changing the filter right now and cleaning the pan. I just bought this truck with no cp3 because the old one was out blah blah blah... we’ll see what fresh fluid, new spin on and inner filter do for it.
 
Will L. said:
Coolant in atf? Cracked cooler line in the radiator side tank will do it
Click to expand...
No coolant just plain ol water. Wasn’t the problem though. Changed the filters and put the pan back on and got the same thing. Took the pan back off to pull the valve body off. I was pulling the solenoids off and the one that’s on top of the valve body (the farthest one up) was SCORCHING hot. I mean 1st degree burn hot. I pulled the valve body off and as i took bolts out i had clear water streaming out. The truck has had the hood off so it’s collected lots of water. I didn’t wanna mess with new solenoids so i just got on ebay and found a reputable rebuilt valve body for a decent price. Just ordered it 10 minutes ago and it’ll be here next week. I’ll update once it gets here and see if it fixes it.
 
Allison's are VERY easy to rebuild if it comes to that. But hopefully the new valve body will do the trick.

Sounds like water shorted out the solenoid. I'd still confirm you dont have a short to ground in that circuit though. Nothing worse that plugging in a new part and it failing instantly from a shorted wire. Been there before....
 
Rockabillyrat said:
Allison's are VERY easy to rebuild if it comes to that. But hopefully the new valve body will do the trick.

Sounds like water shorted out the solenoid. I'd still confirm you dont have a short to ground in that circuit though. Nothing worse that plugging in a new part and it failing instantly from a shorted wire. Been there before....
Click to expand...
I don’t have a new wiring harness coming with the valve body. I’ll check all the wiring just to be safe.
Rockabillyrat said:
Allison's are VERY easy to rebuild if it comes to that. But hopefully the new valve body will do the trick.

Sounds like water shorted out the solenoid. I'd still confirm you dont have a short to ground in that circuit though. Nothing worse that plugging in a new part and it failing instantly from a shorted wire. Been there before....
Click to expand...
I wouldn’t mind rebuilding it if it’s easy. I wanna do some power mods to the motor so it wouldn’t be bad to build it some anyways.
 
Will L. said:
How did the water get in there?
Ive seen people drive through flooded paths and such. Sometimes swapping a few parts saves it and other times a full rebuild is the only way.
Click to expand...
I assume from the dipstick tube being open with the hood off. Unless some idiot purposely poured water in it. It pulls really good when it would. Then just act like you put it in neutral
 
Rockabillyrat said:
Those codes are for the pressure switches. You need to monitor your pressure switches with the scan tool and see if they are switching when they should be. The codes sets if it sees the switch close when it should be open. TCM commands a solenoid and uses the pressure switch to confirm physical movement in the valve body. So if it commands a solenoid it should see a change from the pressure switch. It could be a bad wire, pressure manifold switches, or even a stuck valve in the valve body.
Click to expand...
Just was rereading over the ideas, and that solenoid i said was extremely hot was stuck. I ended up breaking it taking it out of the valve body. The metal part broke away from the plastic part. The little needle plunger thing would stick whenever i pushed it in then had to work with it for it to come back out. The new valve body assembly will be here Thursday. Very confident that will fix it.
 
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