trans problem?
 

Hi everyone! I've got some transmission problems I'm hoping someone might be able to help with some info. I got a 06 hhr and it won't go over 35. Its got two codes p1818 (tfp valve) and p0977 (shift solenoid). would i have to have just the valve and solenoid replaced or a rebuild?

A quick Google search indicates a possible faulty TCM , bad shift solenoid or simply flush the trans fluid and change the filter. One post suggested it could be the MAF sensor
Seeing as the P1818 was the first code it most likely set the other code, therefore I suggest reset the TCM and ECM by disconnecting the neg battery terminal in the spare tire well, place a folded towel on the hatch latch so you don't get locked out, wait 30 minutes, then reconnect the neg terminal.
When the MIL comes back on have the code read and post it up here, it could be the terminal to the TCM has a loose connection or has just needed to be reset also check the under hood fuse box ensure all fuses and relays are pushed in and seated firmly.
First step , let us know

Well one and done!!!
My HHR 2007 2.2 auto had the issue pop up yesterday with the auto lock not working or the cruise! I connected my code reader and it showed a pending P1818 code.
I disconnected the negative terminal at the battery and inspected the negative connections at the transmission and the rad cradle, clean and tight!
Reconnected the battery and everything is back to normal, for now I'll keep you posted!!!

I got Transmission Neutral Safety Switch Short Circuit To Battery

Read more: P1818 Transmission Neutral Safety Switch Short Circuit To Battery OBDII Engine Light Trouble Code | Engine-Codes.com

Sounds like a ground wire somewhere.

While the battery was disconnected I did check the ground wires at the transmission and the rad cradle both were snug, I believe I might have caused the issue when I took the shifter out to replace the indicator bulb , we'll see