On the way home from the lake today, towing our boat (4500 lbs) about 30 miles from home noticed the engine light on but the truck is running fine doing 65MPH, all the guages read fine, figure it's something, so I slow down some and keep going. Come to a stop light red, stop, and go when it changes, notice the motor isn't pulling hard but the RPMs are going up faster than we are accelerating, I'm in tow haul mode. Once it get's to second gear higher gears it seems fine. So I start babying it the rest of the way, more lights, more slipping in first. Got home, it's have a hard time pulling itself in first gear into the driveway. Reverse seems fine when I back up, just first seems to be slipping bad. Transmission fluid is dark and smells odd, but level is fine I changed the filter quite sometime ago and filled the filter up before putting it on, but other than that, nothing unusual about the transmission. Moved the magnet from the old to the new filter. It's under warranty with only 10,000 miles, and all stock except a nictane filter, so there shouldn't be any problems getting if fixed under warranty I guess. Will call to have the dealer pick it up Monday.


First time I have heard of a transmission problem with an Allison in first gear on a stock truck never towing anything heavier than our boat. Any thoughts on what happened? I assume this is pretty unusual? Edited by: srode

How many miles on her? Any performance chip? You been flooging her?

10,000 miles, no chips, it's driven easy 98% of the time. Passed a couple cars to and from the lake and had the pedal down for that, and a couple hard throttles in town to get clear of cars for lane changes, no big hills or anything other than the ramp at the lake pulling the boat out of the water.


I haven't driven the truck any harder than 99 Jeep Grand Cherokee with 100,000 miles towing the same boat, and never had any drive train problems with the Jeep which is rated for much less capacity towing.


Think it's the torque converter or the clutches in the trans?

Checked it out some more this morning. The trans fluid is a little darker than normal, but not dark, and smells off but not burnt. Guess last night in the failing light I didn't assess that as well as I could have. Onstar guy says P0700 code is in the computer. Anbody know what that code is?

No other codes?



The P0700 is listed twice in Helms, once under LB7, once under Transmission. It is a type A DTC.



Basically all it says is the transmission control module is requesting
the DTC and the MIL, which are set by the engine control module.



The diagnostic procedures have you check for some poor connections and
grounds, then replace the TCM. Under the LB7 diagnostic procedure
it eventually has you replace the ECM.



Not much help, but you probably should go get it looked at by the dealer.



Dennis

There are codes stored in the TCM that will be the key to resolving the problem you are experiencing.


If it was a converter failure I would assume you would see some temp spikes. In first gear C1 and C5 are engaged and C1 is engaged right up to OD. You say it shifts fine out of 1 st gear.


C5 clutch is only used in reverse otherwise. Can you fell converter lock up in OD ?


This is an interesting but unique problem. Let us know what code the dealer comes up with if you have no access to a TCM code reader.





Mac

Well I drove it over to drop it off at the dealer this morning, but they don't have an overnight drop box, so will drop it off tomorrow morning. Odd thing, it drove and shifted fine the whole way there and back, incuding full throttle starts from a dead stop. Of course it didn't have the boat behind it, but thought if it was slipping it would do it without it too. Maybe turning it off and restarting reset something? Almost seems like limp mode reset occurred, but didn't think if it was in limp mode that it could do 65 MPH @ 2100 RPMs like yesterday when it was acting up. Tried starting and restarting a number of times to reset the SES light, but it's still on too. Thought the light would go out after 3 restarts if it was limp mode too. I switched it in and out of OD and Tow haul mode while driving it. The OD off I could feel it down shift and upshift when engaged, but don't know if the torque converter was locking up or not, couldn't really feel that. Guess I will find out tomorrow what they find if they can get to it. Will let you know what I hear. Edited by: srode

When the Allison goes into limp mode it is stuck in one gear and no reverse. It would appear to be slipping excessively when starting off in third gear.


But you said it shifted ?





Mac

Yep, it shifted. And it ran and only 2100 RPM at 65 MPH so I don't think it was stuck in 3rd gear.

srode

Sounds like you might have hurt the converter clutch and overheated the trans which would put you in a limp mode ( 3rd gear start). I think that explains slipping in first gear. This would also explain dark smelly fluid. When the Ally cools down and ignition switch cycled again you were out of limp. This is an educated guess on my part.
mike

Here's what I got from the dealer work order today


10584 FOUND TROUBLE CODE P0747 TRANS PRESSURE CONTROL SOLENOID STOCK ON IN THE HISTORY DATA CALLED TAC CENTER WITH CASE #7732965 AND RECOMMENDED TO CLEAR TROUBLE CODE AND ROAD TEST VEHICLE AND IF CODE DOES NOT RESET INDICATE GLITCH PROBLEM AT THIS TIME TIS UNDER INVESTIGATION K9995


The Service manager told me on the phone when he said it was ready to go that GM knew of the problem but has not come up with a fix for it yet.


They also fixed the Haunted seats (see the thread under 2500HD Trucks) with a poor ground and setting U1041 loss of communication with the ebcm due to poor ground under driver door on the chassis, cleaned and cleared code N9502