4L80E Tranny issues

[wally Gordon]

I am new to this site, Please excuse me as I'm not sure what I am doing. I recently purchased a 94 GMC Sierra K2500 Pickup. 6.5 turbo with a 4L80E tranny. I lost Overdrive, and received codes 15 and 81, (coolant temp sensor and 2-3 shift solenoid) I replaced coolant temp sensor and all shift solenoids, filter and fluid in tranny. Cleared codes from ECM, I now have no codes, no check engine light, but still have no overdrive. Any ideas on what I can check next? Does tranny need rebuilt? Any help would be greatly appreciated.

 

[ak diesel driver]

Check that the temp sensor in the coolant crossover is functioning properly. It's the one the PCM uses.

 

[wally Gordon]

Check that the temp sensor in the coolant crossover is functioning properly. It's the one the PCM uses.

Thanks AK diesel driver, that is the sensor I replaced, however, I will check to ensure proper operation. I appreciate your help.

 

[wally Gordon]

Thanks AK diesel driver, that is the sensor I replaced, however, I will check to ensure proper operation. I appreciate your help.

The sensor appears to be operating properly, water temp 46 degrees=4850 ohms, water temp 73 degrees=2780 ohms, 160 degrees = 625 ohms, this seems pretty consistent with the Chilton repair manual I have.

 

[THEFERMANATOR]

Is there a t-stat in the truck? Is it getting up to temp? If the engines cold, it will lockout od. Code 15 i believe can also trip for cold engine temps like from running cold to long. Really need to get a scanner on it and see what the ecm is seeing, otherwise were guessing blind here.

 

[wally Gordon]

Thanks Guys,
I did replace the T-stat. it was defective, stuck open, check engine light now comes on after driven for a few miles, code 15. I had OD until the engine warmed up. I have ordered a OBD II scanner that will also read OBD I vehicles, my truck is OBD I. When I receive it, I will see what I can find out. I appreciate your help.

 

[THEFERMANATOR]

Just a heads up, most obd1 scanners cannot read the 6.5l. It was a 2 year redheaded stepchild not really supported by the aftermarket. I would reccomend investing in gmtd scantech software as it is just for the obd 1 6.5's.