My 2011 HHR LS 2.0 is acting like the torque converter clutch is engaging at lower speed than it should and doesn't disengage until the car is almost stopped.
when accelerating it almost feels like I'm "speed shifting" with a manual transmission. When slowing down and just before breaking to a stop the engine will shudder just like a manual transmission would if trying to stop without depressing the clutch pedal.
I'm thinking it might be the TCM or ECM but don't know how to test for that.
I just bought the car so I don't have any of the previous repair history other than the Carfax which doesn't include any mechanical repairs.

 

The piston bore of the lockup solenoid valve is likely out of round. They get an oval shape and the valve will hang up.
It could be something else but that is common on high mileage trannys. How many miles on yours?

 

I have 150k miles on it.

 

FYI. There is no 2.0 engine in a 2011 HHR. LS would have been a 2.2.

 

There are OBD2 codes for the transmission solenoids/valves. Are you forgetting to mention a CEL?
There are probably a bunch of transmission repair shops that would do a free diagnostic, or include the cost in the repair.
Why jump to "the computers are bad"? They might be on the list of possibilities, as the very last thing not the 1st through 20th.

 

I do not have any CEL codes present or remembered in the DTC.

I did make an appointment to take it to a transmission shop on Monday

 

If your HHR has a lot of miles on it, it may only be the turbine shaft seal is worn out.
Has it had a recent trans oil change and did they use Dexron 6? They may not have changed the oil pan filter also.

Clare

 

You may be describing what my 2008 2.2 did. First noticed it at maybe 30 to 40,000 miles? Space It was subtle. It was intermittent. It did not cost much trouble. I mostly ignored it. I thought maybe it was doing a bit of hunting for the right gear, maybe because of a knock sensor response, so I tried a tank of premium fuel. That seemed to make a difference but it’s impossible to know, because again, it was intermittent.

It came and went. Mostly went. Sold the car with maybe 110,000 miles?

If it was a slight knock, it may have been caused by a little carbon buildup. This is plausible because mine never did it when it was cold, only when it was well warmed up.

Using top-tier fuel, and or a detergent additive for a while, might help.

If your problem is as subtle as mine words, I would try a tank of premium or just ignore it.