That's a long grade, but in near-freezing temps I'd be surprised if the trans fluid actually got that hot, unless your cooler isn't functioning properly.

I've had my AT temp light come on while rock-crawling on an uphill trail, and while towing a 1500 lb trailer up a 5-7% grade, but both instances were in the AZ summertime with ambient temps around 100 degrees. I have an auxiliary trans fluid cooler installed in addition to the stock radiator loop.

Wait, wait, wait.

So did you get an A/T overheat light or did you not? Be more clear.

John B.

I can say its hard to get on (over heat light) if your moving...... I towed a trailer 5500-6000 lbs and on top of that a good 800 in crap in the montero. Motor at 4500k for a good 6hr non stop in 95f+ heat in TX. It did over heat once.... we Ran with the heat on and windows down. Man that was dumb!!!! was in 3 gear and shifting down to 2 gear going well trying to go 75-80mph

Yes - I got the overheat light. It was in heavy snow and everything underneath was wet.

My sensor wiring appears to have an exposed bit of wiring due to cable sheath wear. This is likely the issue.

I will take my temp gun to measure it next time. The temp light went out immediately after I restarted the truck and the engine temp gauge had moved 0 at all during all this.

No codes are reported in the TCU - this is the newer 1999 model that has the input/output shaft sensors and more codes for transmission slip and other such malfs, so if I were slipping it would tell me.

I think I will replace the sensor. Anyone happen to know what the OBD2 PID is for the Transmission Temp?

does the at temp light come on when you first start it and everything should be cold still? if so then it's a water issue in your wiring. If not and it comes on after some driving, then it's likely something else.

No - it only came on after quite a bit of driving but all of it in the snow.

Just to confirm you know to stop and park in a safe spot as quickly as possible when this happens, put the gear into park or neutral and let the engine idle until the light turns off. If you dont you can destroy your transmission which is $$$ to repair.

When you let it idle does the temp light turn off?

If so, when was the last time you replaced your tran fluid and filter?

I pulled over instantly and let it cool off. I let it run for about 15 seconds and then when the light didn't go off stopped/started the truck. The light went off the instant I did that.

It's a new transmission - new filter, new fluid (Redline ATF D4). No codes in any computer.

Just so anyone else who may read this knows, you do NOT want to shut off your engine after 15 seconds in that situation just in case the transmission is in fact overheating. It is essential that the engine be kept idling in neutral or park for a while, say 15 minutes, if the light stays on, before any attempt at shut-down, before you'd want to rule out an actual overheat and call it a wiring issue. It probably was/is a wiring issue in this case (and not the sensor itself), but just in case...you don't want that fluid to burn just sitting in there.

Even though it was cold outside, the transmission may have been working pretty hard and they can and do get hot. Use low-range whenever you feel like you might need it. If I had to guess at it, four-high-open diff/AWD would probably be the most torturous on the transmission due to the added slip in the center diff. It could happen...

John B.

Looks like there might be some truth to the Diamond ATF III stuff floating around - it has a substantially different friction than Dex III and most synthetic style replacements.

LubeGard makes a Highly Modified Friction adaptation fluid to turn the Redline D4 I have into a true substitute for DiamondIII. I put this in and the transmission now behaves like my last one did on DiamondIII. No more odd take offs and strange behavior at 35mph.

This may have contributed to the A/T light situation.