What would cause my 08 Chevy HHR to all of a sudden start shifting hard? 190,000 miles

 

Is there a CheckEbginLight?
The most common reason is the t-stat is stuck open and the engine is not warming up fast enough for the computer and/or is running below 179F. Use ONLY a ACDelco 131-158!!!!

 

No check engine light. Vehicle runs between 185 and about 216. No warning lights on of any kind on dash. It did this once before about a year ago 🤔

 

Try tightening those 4, 7mm bolts real tight in the under hood fuse box, inspect the TCM connector for corrosion and dirt and any bent pins.
Any transmission fluid leaking out under the car? At the axle seals?

 

Yeah no leaks of any kind but I will try that and get back to you

 

I’ll wait! Thanks

 

Get it checked for pending and historic codes.
Second most common is some fault in the ABS system.

 

Check plugs pins fluid everything looks fine. With 190,000 I'm leaning towards bad transmission or solenoid. It is what it is. I appreciate your insight 👍

 

The 4T45E is a very stout transmission, solenoid problems would set codes.
next I suggest a battery lobotomy, simply disconnect the positive cable at the battery for 15 minutes, then reconnect it. Careful don’t let it touch the body or ground, the RAP is live. And put a rag down on the latch to prevent accidental closing of the hatch door. It’s instinctive muscle memory, the human brain is programmed that way!
Anyways this will reboot the computers and possibly make them work again.

 

Just FYI computer just set p0700. I will give that a shot as well.