P0740 and High Trans Temp

Jonathan Annear · April 16, 2021

Hello Everyone!

I just purchased a 2014 Chevy Silverado WT with 190K, the 4.3L V6, 6 speed trans, and RWD. On my way home, I lost what seemed to be 5th and 6th gear and popped a check engine light. The temp outside was probably around 70 degrees. The truck's transmission would seem to act normally for a short time after being shut off. My wife and I let it sit for an extended period of time and drove home later in the day. On the way, I stopped at an Advanced Auto Parts and ran codes, finding I had a TCC solenoid code. I was also about a half a quart low on transmission fluid. I added some Dextron VI and the truck drove normally all the way home. The temperature outside had cooled significantly. The next day drove it around town and found that if I didn't drive on the highway, I could drive all day with no issues. I sent the truck to my mechanic and while it was with them, it had no issues shifting at speeds from 30mph up to 80mph on extended drives. The check engine light went off on its own. These were also cooler days. They did note that transmission temperatures reached 240 degrees. Picking it up and driving it home today, I found trans temps reached 225. I've been told that I should swap out the transmission with a low mileage salvage yard unit. Before doing so, I wanted to make sure that was the right direction to take. If I needed a replacement, wouldn't it not shift properly all the time? Could higher temps cause the TCC solenoid not to operate? I have seen that there is a thermostat for the transmission. Couldn't this be a defective thermostat causing the issues? Any insight is appreciated!

cmysstailights · April 17, 2021

Trans is toast. Needs a rebuild

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swathdiver · April 17, 2021

How does the fluid look? If it is not "toast", I would get rid of the thermostat and rebuild the solenoids. You can do this on your kitchen table for just over $100 plus fluids.

https://www.amazon.com/dp/B072C63HMY/?coliid=I1NOR87F2HVADM&colid=3MYY1OQK1UL4M&psc=1&ref_=lv_vv_lig_dp_it

I just re-read your post and saw that it may have 190k on it. Well, we've seen them go to 280K or more but most with thermostats don't last half as long as yours has. The OE fluid is shot at about 45K miles.

Edited April 17, 2021 by swathdiver

Jonathan Annear · April 17, 2021

The fluid looks fine. Although, the engine bay has a record of the fluid being flushed two thousand miles ago. I'm guessing this may have caused the issues, which is why the guy wanted to sell it. I just thought if it was toast, then it would have problems all the time. It also seems like if I could get the temp to normal levels, that may solve the problem. It seems the TCC solenoid works until the temp reaches a certain level. I thought the solenoids were part of the valve body and couldn't be repaired. Interesting to know they can be rebuilt! I found a replacement locally with 95K miles for $600. Maybe I should just go that route. Thank you for the responses so far!

Edited April 17, 2021 by Jonathan Annear

cmysstailights · April 17, 2021

I changed my fluid at 60k and it still did it and this time i threw a code. My mechanic never said the oil was shitty when he changed it. He would have said something, trans shop said known issue with these trans. Some r good some r ******

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Jonathan Annear · April 17, 2021

35 minutes ago, cmysstailights said:

I changed my fluid at 60k and it still did it and this time i threw a code. My mechanic never said the oil was shitty when he changed it. He would have said something, trans shop said known issue with these trans. Some r good some r ******

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You had the same issues?

cmysstailights · April 17, 2021

After 1.5 hr drive, Mine would drop from 6th gear to 4th and stay there till i re start the truck. Been happening for 2 yrs, finally threw a code

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newdude · April 17, 2021

If the converter is working and then isn't working, its slipping or being commanded off because its slipping.

If the converter has failed, its been pumping clutch material all throughout. And if its losing 4, 5 and 6, those clutches are probably burnt up which is common.

She's gotta come out and come apart to see what's good and bad inside. If it needs the pump bodies, that gets $$$ quick.

Solenoids are part of the Transmission Electro-Hydraulic Control Module or TEHCM, which is the TCM and all of the valve body solenoids. Its attached to the actual valve body itself that is controlled via the solenoids in the TEHCM. Solenoids won't fix your trans I'm afraid.