So I’m not on this forum until I need to fix my 02 (work truck) as my main line to work on is older Landcruisers. Took a nomadic trip through CO in early June and had the pitman arm snap at the drag link joint about 2 miles from the pavement on some BLM land. Fortunately ran into a few locals camping in the same area the next morning. One of them ran me into town 3 X that day to get a new pitman arm and pullers. After braking two pullers on the trail I limped it to the pavement using 5-6 different ratchet straps. A few straps got demolished (the ratcheting part) as it was difficult to get them lined up perfectly where they did not interfere with anything turning the wheel between 10 & 2:00. A lot of 3 point turns getting out of the trail. I got a flatbed to haul me into Rifle CO where a super nice shop owner stopped his current work to get me back on the road. I’ve never paid anyone to work on this truck but was never happier to do so. Felt a lot better when he had to use a cut-off wheel and air chisel to remove the old pitman arm. I say all this because ever since this happened my trans temps started creeping over 200 and upwards of 220-225. At those times I would pull over and let it cool down. Got home (TX) and did a fluid change (both filters) and hauled one cruiser between Austin and SA (late June) and zero temp issues. From that point on I can’t drive 20-30 miles without the temps spiking to 220+. Check engine light comes on and I took a pic of the recent codes. My first thought was removing the steering box on the trail (to access the pitman arm with my 1/2” gun) I damaged or kinked some cooling lines. Upon further investigation it’s obvious I did not affect any because they are on the passenger side. Disregard the fuel sending unit code as that’s never worked since I bought this truck from the original owner 13 years ago. Also, I swapped in a used Allison about 100K ago (longer story on how I screws up the 5th gear clutches). Any chance my internal filter (Napa) could have dropped into the pan or anything else weird happening? When I changed the fluid in June (after the CO trip) the old oil looked and smelled as good as the new fluid I put in. Any thoughts or suggestions are welcomed. Here’s some pics of where she broke down on the BLM land as well as the codes I’m getting. Thank you. Jimmy.
2002 Allison spiking heat temps
- Thread starter Mcguirejohnson
- Start date
225 is nothing for these transmissions. But you are going to need a better scanner to access the codes in the transmission. That P0700 is saying there is more in the transmission to look at
Great point. My oldest son Is a Toyota tech and bringing over his Snap On computer next week. I’ll have him run the codes and post up what we find. Appreciate the feedback.
Never seen a P1621 on a stock ECU, only with an emulator soldered in (e.g. RoadRunner). Interesting.
The Snap On scan tool should read the real transmission codes, which will hopefully let us know what is happening. It is possible that if the torque converter isn't able to lock it would run warmer.
The Snap On scan tool should read the real transmission codes, which will hopefully let us know what is happening. It is possible that if the torque converter isn't able to lock it would run warmer.
Had that code come up a few times on me previous LB7. Didn't seem to affect anything. Didn't have the road runner mod on mine
From my research, if I'm remembering correctly, is it means one or more memory sectors gave an error. I believe the memory is ECC (error correcting code) type so it is able to compensate for it. And no need to do anything unless are experiencing an actual issue with it's performance.
My bad as I left out some critical information. Performance wise it does not drop into limp mode but the trans will down shift rough when the temps get around 205+. If I coast into a stop it slams pretty hard as I get close to 20-30 mph. If I feather the fuel while coasting it does not do this. When I lost 5th gear with my orig trans it would go into limp mode so familiar with that. This trans came out of a similar mileage (same year) truck and now has 285k on the ODO.
Appreciate your response. Could you provide a bit more information? Keep in mind this 02 Duramax is the newest vehicle I own so not a lot of experience with sensors. Are you saying a “bad wheel speed sensor” can cause the trans to heat up or just the hard downshifting once hot? Also, where would these sensors be located on the truck? Thanks again. Jimmy
Not necessarily when "hot" bit the transmission does have different shifting strategies for different temperatures. When it receives speed information that is either not consistent, drops out or is wrong then the transmission has a hard time executing the shift in the time it has to complete it. Thus a hard down shift
You should have one speed sensor on each of the front wheels on the hub. Remove them and make sure the surface is clean and free of rust. Make sure the tone ring inside the hole is clean and free of metal or other debris. There is another that is normally on the back side of the transfer case that does the rear wheels. Make sure it is seated properly and no wiring damage.
Great feedback. So if I’m thinking through this correctly my #1 issue may not be the speed sensors if the hard downshift is occurring after the trans temp spikes. Thinking I need to pinpoint the temp spike issue first, but will definitely pull the 3 speed sensors and inspect them. Thank you for the responses. Jimmy
From my recollection, most report the hard downshift only after the transmission is up to temp. Not while warming up. So while you may have other issues don't rule out the speed sensors.
You are probably going to need to put a scan tool on it that can monitor slip and see if any of the clutch packs are slipping. Especially the TCC. Any slipping will heat the fluid fast
You are probably going to need to put a scan tool on it that can monitor slip and see if any of the clutch packs are slipping. Especially the TCC. Any slipping will heat the fluid fast
Had all the same thing with my 02 gmc , it was the TCM temps going over 200 and the hard shifts 4 to 3 and 3 to 2 , got some hard upshifts too , with over 900,000 mile replaced the TCM and all is good , I didn't have any codes ? , been 6500 miles and working good with used TCM out of a 01 , had to do a reflash to the 02 programming , temps dropped by 40 F after the new TCM ?
Thank you for the last few comments. My son ran the codes and came up with the P0776. So the TCM sounds like a probable issue and he’s researching how to test this unit for me. Want to see how to diag the TCM and avoid throwing high cost parts at it if not necessary. Really appreciate the input. 
Quick update. Have never paid anyone to work on this truck but bit the bullet. My son (he’s the Toyota tech) did some diag with his Matco computer and had a hard time dialing in the issue. He recommended I take it to his high school friend whose brother owns CenTX Diesels out of New Braunfels. I did and they were great. Identified an issue with the internal wire harness. It was a 3 hour job and about $75ish for the part. Drove it about 30 miles to the house yesterday and did not get above 94 degrees (outside temp was 95). Their tech also found a PO875 & PO848 code which they said points to the neutral safety switch. Being external (like .84 hours by the book) they recommended I take care of it myself. This seems to point to my intermittent harder downshifts I’ve experienced for many years. The GM part# is 29540479 (I believe). Appreciate everyone’s help and feedback on this.
If the bolded statement is true then you have a major issue with the gauge or sender. It is impossible to be colder than ambient temperatures, especially while driving.
I get that and makes total sense. Should have stated that the temp was slowly climbing while driving (all country farm to market roads) to my place. Max speed limit of 60mph. It hit 94 degrees just as I pulled into my neighborhood. Actually thought about driving the additional 6 miles to HWY 281 and then airing it out a bit with the cruise control to see where it would max out at. A few weeks prior taking a load of house recycling to the county location (5 miles away) and all nieghbor hood roads not exceeding 35 it heated up to 228 and went into limp mode. Jury is always out until I can vet it completely and appreciate your feedback.
Even so, the transmission should be close to the engine temperature after 30 miles. The transmission fluid goes through the engine radiator so if the transmission is colder then the engine then engine heat will flow into the transmission.