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Transmission overheat trouble

kmccoy

kmccoy

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I have a 2003 Chevy Silverado 2500 HD Duramax 6.6 with a 5 speed Allison transmission, 130,000 miles. I’ve been fighting this problem for months. Three months ago I drove the mentioned vehicle for about two hours and parked it in the driveway like I always do everyday. The truck runs and drives great. I had to have injectors replace in 2017 and installed an air dog lift pump. Been running great. The truck sat for two weeks, it started up normally and ran fine. I let it warm up for 10 - 15 minutes. When I got back in the Trans temp gauge was pegged, the buzzer was dinging and Transmission overheat Idle engine appeared in the instrument cluster. The fluid was at normal level and a little dirty but not horrible. The trans cooler and transmission pan were warm to the touch in no way was the transmission overheated. The vehicle sat over night. Turned the key to on, gauge pegged into the red and got the same message on the dash. I don’t have to even run the truck.

I did some research and upon checking I found trans fluid in the connector at the back of the transmission. I’ve replaced the transmission internal wiring harness, the internal and external transmission filters and replace the fluid. Same problem, same symptoms. If I drive the truck it runs fine but it shifts erotically. I inspected the wiring and connectors to the Transmission Control Module (TCM) found nothing. I sent the TCM in to be checked and repaired but they forums nothing wrong with it, sheared the codes, programmed it and returned it to me. I installed it today. Same problem and symptoms. Drove the same as well. Trouble codes P0218, P0736, P0736,P0741, P0836 and U1096. Im thinking the last 4 or 5 codes are from test driving the truck.

Any suggestions?
 
Do not drive it anymore until the false temp warning with key on is eliminated. The computer will start doing all kinds of incorrect changes trying to protect it but actually can hurt it.

I think a critter became a squatter while you moved out for two weeks- he took over and had some copper spaghetti dinner but thats a wild guess- a dangerous assumption, so let's get to actual diagnostics first.


It’s easy, common, and almost always a huge mistake to start throwing parts at it.
Remember new parts don’t always mean good parts and if you swap parts hoping, and the new part is faulty, it will severely complicate the diagnostic process.
So anything you do install, keep the old one and remember this possibility.

The harness find was good catch and correct to replace. But with the cheap chinese knock off parts as common as the quality ones- gotta ask where you got the harness because Ive seen a couple horrible new failed cko harnesses and Im not seeing a lot of harnesses lately.

Were the codes exactly the same before and after the harness swap?
Did they clear & come back or never would clear?
How the TCM repair place found nothing wrong - then why did they reprogram it???!!! If it was fine having it reprogrammed when good throws a red flag - imo.

Take the time to remove, clean & reinstall all the grounds for the front harness, including both the battery cables at both ends. While batteries are disconnected individually battery load test them. While ground issues are more likely and weak battery less likely but possible.

When done doing the grounds- inspection of the harnesses particularly the trans circuitry for damage from rubbing or rodents tracks/droppings and obviously chewing damage. The harness where it goes into the cab is less likely but possible.

Are you getting the reverse codes BEFORE shifting into gear? If so that’s a HUGE clue that these are all false codes not just the trans temp being false. Cant have a 736 without actually moving in reverse. And to have this assortment really indicates one common electrical issue to me.
Especially how you cleared the codes then restart and have temp shows high within first minute on a cold transmission. Getting actual measurements of the trans temp and compare to what the computer says helps here. The quick assumption becomes faulty sensor if different but not with all the other stuff happening.
I fumble my way through trans and especially the ally, but there are some guys here on point with them. Give a couple days for them to check in here as their knowledge is worth it. The default call here always will go out to @THEFERMANATOR

(To the other moderators doing the @ link didn’t pop in his name like normal-
Just a hiccup or is something up? Haven’t seen anything from Ferman in a minute- everyone else that will -join me in payer for him right quick hoping he’s ok)
 
Thank you for your response and pleasure to meet you.

To answer your first question. I purchased the trans parts from Rock Auto ( internal harness, internal oil pickup filter, external red filter, pan gasket, and temp/psi manifold. I use Castro TranSynd TES 668 trans fluid. The fluid I dropped out of the trans was dirty but not horrible (needed changed.)

I do have a reverse code P0736 but I believe this if from driving the vehicle. The codes will not clear with the OBD (says clear failed) or after removing the battery cables over night.

Trans temp Live data on the OBD is 298 F while the actual reads 102-109 F.

Both batteries are 4 years old and passed load tests at Napa. Since reinstalling the TCM and batteries, the charge light glows very dimly. It’s never done that before.

When this first happened I noticed the insulation on the fire wall at the rear of the engine was missing, thinking it was a rodent or something I checked the wiring harness but did not find anything. (I could have missed something.) Now that you mentioned that, I think I’ll do a little more investigating.

Also, I haven’t checked and cleaned the grounds. I did pull apart electrical connectors, inspected, cleaned, and reinstalled to check proper fit.

Thank you bunches. I was starting to loose hope but you’ve put me back in gear to find this problem without taking it in to a dealership. Our local dealership is a lot to be desired and untrustworthy. I’m sorry to say and I don’t like to talk bad but 210.00 an hour is crazy nuts.

Thanks again and I’ll be checking the site regular.
 
And yes, I have kept all the old parts. The harness looked good and I ohms checked each pin for continuity and placement. They new manifold had two less buttons but information stated the two missing buttons were not needed.
 
If the batteries has removable caps.
Go to the parts store and get a hydrometer. Check each battery cell.
Temps went to -32*F below zero. After almost a week it warmed some so removed the batteries and took them into the heated garage.
As @dbrannon79 suggested, popped the caps and did a visual, most cells had ice formed within. Thawed the batteries then charged them for about four hours. They were both at less than 2 amps charge rate.
Checked the voltages with a multimeter then did the draw test.
Both batteries tested good.
Got out the hydrometer, one bad cell in one battery and two bad cells in the other battery, so now, near $400.00 poorer there is two new AC Delco batteries in my truck and does it ever spin over on the starter now.
Another bad battery story.
My friend has a GMC Escalade, inline engine. He spent a lot of money to get this random misfire problem solved, dealership and indy.
Everyone fired the parts cannon at it and he bring it back home, a day or two later engine misfire.
One day he was poking at the problem in the WWW. A technician had his own blog site, talked of the exact same problem on the exact same vehicle, blogged he changed the battery and the problem has never returned.
Bob took his Escalade to the parts store, had them install a new battery, his misfire has never returned.
I hope that You dont just go firing fhe battery cannon at Your truck but do a thorough investigation on those “ GOOD “ batteries.
Get a hydrometer and test them.
If You buy a hydrometer, get one with the good squeeze bulb and the glass tube about an inch in diameter.
 
Still looking. Does anyone know if there in a wiring harness that runs through the valley in the center of the engine? I found a big mouse or rat nest in it, but can not see any wire harness. I tore out the fuse box and checked the wires running to the TCM and ECM and found nothing. Is the temp sensor from the transmission harness go through there, because I’m it doesn’t seemed like it.

Reminder, I only have transmission code P0718, ( trans over heat) no engine codes.
 
kmccoy said:
Still looking. Does anyone know if there in a wiring harness that runs through the valley in the center of the engine? I found a big mouse or rat nest in it, but can not see any wire harness. I tore out the fuse box and checked the wires running to the TCM and ECM and found nothing. Is the temp sensor from the transmission harness go through there, because I’m it doesn’t seemed like it.

Reminder, I only have transmission code P0718, ( trans over heat) no engine codes.
Click to expand...
Makes me think that it might be a transmission temperature sending unit problem.
Someplace, maybe even in the service/repair manual, there is a chart that will show the various amounts of resistance at certain temperatures.
Using a pan of water and a meat or candy thermometer and a multimeter clipped to the sensor, then heating the water and monitoring the temp probes You should be able to figure if the sensor is at fault.
 
P0218 =trans over 290 code but you said the temperature wasn’t that high really
P0736= reverse incorrect gear ratio
P0741=torque converter clutch not engaging or disengaging
P0836=problem with 4wd switch circuit
U1096=failure to communicate with instrument panel cluster (dash)

But you think the first one is the only problem?

Where the nest is doesn’t matter. It could have made the nest innthe bed of the pickup where no wires are. It has chewed up the harness in at a minimum in one place- maybe more. Like a thief you saw that piled up stuff in your living room and ate some food & spilled it in the couch- it doesn’t mean he didn’t go into every room and break things or take things from all the rooms.

It could have been inside the cab- up under dash too.
The TCM is next to the driver side battery on the shroud. For a rodent that is 0.03 seconds away from his nest you found. Start at that harness and go from there.

Something you could try but you need to do this very carefully is make sure it isn’t the connector going into the tcm. Here is a video showing it. But I really doubt this is your issue. I think the critter was making nest material from this harness and a few wires are intermittently shorting to each other. But this is not a bad idea to do once every 20 years.
 
Thank you, I’ve seen both videos and checked after placing the internal harness. Harness, connecter, and pins fine. I even took apart the TCM harness all the way back to the fuse box. Pulled the fuse box, checked and rewrapped the wiring underneath that. Found nothing.

I took out the ECM under the battery and checked the harness and connector as well. Still nothing.

The above was checked by a friend as well to make sure I had not missed anything before reinstalling.
 
It is possible you just have a bad temp sensor. Just the list you had in first post pointed me where it did. Then you confirm a nest on the engine and that makes me hard pressed to think otherwise.

If you start firing the parts cannon then the sensor is top of the list.
But I can’t let go of “casa de critter” being most likely.
 
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