Tranny issue not setting any codes.

[BigDiesel]

My truck just started hunting in and out of OD(mostly out) and the TC lockup has been in and out as well. It ran perfectly up to that point. I put a scanner on it yesterday and all I get is a P0118 - Engine Coolant Temperature Circuit High Input. I'm going to be dropping the pan in the next couple of days to change fluid.(and prolly change a solenoid or two :rolleyes5:)
How come this doesn't set a code?
I'm leaving for Vegas with the truck this sat and need it fixed by then.
Any ideas??

[DmaxMaverick]

It DID set a code, and you read it. The ECT value will effect tranny operation. Fix the ECT code, then address the tranny, if it is still a problem.

[BigDiesel]

I was thinking it would set a tranny specific code. Didn't think the ect would affect the transmission operation directly. Fixed it right up.

[DmaxMaverick]

The PCM will command several modes of operation for the tranny, depending on conditions. One of them (I suspect, in your case), is the warm-up cycle. If the PCM "thinks" the engine is cold, it will inhibit some tranny functions, including OD and TCC, which expedites the warm-up (higher engine speed and open torque converter). To the PCM, this is not a tranny fault, but a tranny mode adjustment to accommodate an engine condition. The reason you had no tranny code. And, as proven, there was nothing wrong with the tranny. Sometimes, it's best to not try to out-think the engineers. They don't always get it right, but they are smart fellers, for the most part.

[GMC Hauler]

The PCM will command several modes of operation for the tranny, depending on conditions. One of them (I suspect, in your case), is the warm-up cycle. If the PCM "thinks" the engine is cold, it will inhibit some tranny functions, including OD and TCC, which expedites the warm-up (higher engine speed and open torque converter). To the PCM, this is not a tranny fault, but a tranny mode adjustment to accommodate an engine condition. The reason you had no tranny code. And, as proven, there was nothing wrong with the tranny. Sometimes, it's best to not try to out-think the engineers. They don't always get it right, but they are smart fellers, for the most part.

Exactly.

I had this problem, the wife was driving to Illinois and I was in CT. I troubleshot over the phone. If the PCM sees a open on that temperature circuit, it disengages the OD.

I bought a new sensor, and guess what came with the sensor? The plug and some wire. That turned out to be my exact problem. My sensor was good, the wiring harness was bad. Think the aftermarket knew something when they threw the wiring and connector in the same box as the sensor? I bet on it.