My radiator blew last week so I replaced it and flushed the system. Now the transmission (My guess) is having trouble shifting between 3rd and 4th. Not all the time of course but when it happens I feel the truck surging in between gears. I took it to the dealer and they ran a diagnostic on it and found nothing. They did say that the engine and tranny may have to reprogram itself to find the correct rpm to shift at. Please let me know your thoughts. Thank you in advance!!

 

Forgot - 2007 H3 127,000 miles

 

The dealer is full of chit. The tranny has no "programming", and is controlled exclusively by the PCM in 2006-7s. So if you have the original PCM and nobody re-programmed that, it has retained its original settings and there is nothing to learn.

Two things may have happened. 1) I do not know what you mean by "radiator blew" but if it leaked coolant into the trans, well that is not good and will cause problems; 2) independent of that, 127K miles on a 4L60E is right near rebuild territory, even if you have changed the fluid and filter a couple times. Slippage is Mr. Rebuild's calling card.

When was the last time the Trans fluid & filter was changed? You can try that to see if some crud is stuck in the valve body and maybe get lucky, or take it to a trans specialist.

 

Thank you for you r reply!

Radiator blew = The radiator cracked on the top and the fluid came out. It had no tranny issues prior to the overheating. After replacement of the radiator I noticed the tranny had trouble shifting from 3rd to 4th. Doesn't matter if it is hot or cold. It was 34 this morning on my way into work and still the same issue. Why would a problem arise in the tranny after overheating?

 

100% coincidence is a very good possibility.

Please understand, ATs' worst enemies are 1) dirt/crud; and 2) heat, which can scorch fluid and reduce its function. So there could be a minor relationship to the radiator not cooling like it should, or just be a coincidence. Hard to say.

 

Looking at the simple stuff first, there are transmission coolant lines that go and from the radiator, at least on my H3. Replacing the radiator would result in some loss of ATF when these lines were disconnected, perhaps at least the amount in the cooler cavity itself. Assume you've checked the ATF level as per the service manual after replacement and replenished any that may have been lost.

 

Unfortunately I didn't have time to replace it myself so the radiator was replaced at the GM dealer. I would hope they would check fluids after the install as they have been in business for many decades and have a great rating. I will double check to be sure. Thank you for your advise!

 

Checked the fluid level and quality, Fluid level is good and fluid is fresh and clean.