My wife has an 07 Hummer H3, 5 cyl, auto trans. Recently at around 50-60 mph the auto trans comes in and out of lock up. Other than that it shifts and drives fine. I've searched but found mixed results, some say replace TCC solenoid or other items but I'm not clear on how I can test this to be sure that the TCC solenoid is the issue and also how to fix it. Any help is appreciated. Thanks! Chris

 

How many miles on the trans, and how many miles since the last trans fluid/filter change?

When the 4L60-E can't hold full lockup, it is usually because of heat and crud.... and if you are over 100K miles, might need a rebuild. If you are lucky, a Trans fluid and filter change might be all that is needed, unless the crud already did some damage.

 

ah funny you mention that. It has 120K on it now, but fluid and filter were changed at 60. It definitely needs it again. My wife drives hard. It also has a ruptured oil cooler line (it rusted away and now has a pin hole), which I am also fixing. Sounds as if I should fix the cooler line, flush and replace the filter and see if that addresses the issue. Thanks!

 

At 120,000 you may want to replace the radiator too.

Read about the issue with the radiator separation and coolant getting into the transmission.

 

Thanks all. Actually I replaced the radiator last year. A hit to a deer took care of that!