2ofthemincali

have a flat-lined temp guage and the A/C doesn't work, that leads to the engine light coming on and the remote start not working. took to dealer and it just started working again after tech messed with connections. was charged 2 hours of labor for that round of head scratching. after 1 week went by temp guage flatlined again and A/C stopped working, followed by the engine light and no remote start a day later. took back to dealer and they said the thermostat needed replacing and it would cost $326! told them no thanks, it's an electrical problem. dealer said that the car wasn't reaching operating temperature however the car was getting up to 199 degrees while I was driving it. since the temp guage wasn't sending of course it would read as not reaching temp. after the tech messed with the connections at the dealer it started working again however they stuck by their diagnosis that it was the thermostat causing all the trouble. everything working now but I'm sure it will go back to having the same problem soon. anybody have this issue with their HHR? bad grounds maybe? help!

ChevyMgr

Did they tell you what codes were set?

GDZHHR

Check out this thread..........
https://www.chevyhhr.net/forums/show...light=flatline

This has happened to a few of us.

2ofthemincali

dealer said that's the only code showing.

2ofthemincali

thanks for the info. not getting why if the thermostat sticks the temp guage flat lines though, seems like that's when you would need to have it the most! guess that's what you call progress huh? and what kind of engineering genius makes the thermostat where it takes $326 bucks worth of effort to change it? what a moron! is there access to a shop manual on this site somewhere so I can change that out myself? thanks for all the help, very much appreciated!

ChevyMgr

I will assume then that the DTC was P0128 (Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature). Replacing the thermostat is the usual repair for this code.



2007 Chevrolet HHR | HHR (VIN A) Service Manual | Document ID: 1833247
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Engine Coolant Thermostat Replacement:
Removal Procedure




Drain the cooling system.
Reposition the radiator outlet hose clamp at the thermostat housing.
Remove the radiator outlet hose from the thermostat housing.



Remove the thermostat housing cover bolts and cover.
Remove the thermostat.
Remove and discard the thermostat housing O-ring seal.
Installation Procedure




Install a NEW thermostat housing cover O-ring seal.
Install the thermostat.

Install the thermostat housing cover bolts.
Tighten
Tighten the bolts to 10 N·m (89 lb in).

Install the radiator outlet hose to the thermostat housing.
Position the radiator outlet hose clamp at the thermostat housing.
Fill the cooling system.

2ofthemincali

will go fetch parts home on monday and give it a try. thanks for the help, looks plenty do-able. I do appreciate your expertise! it sure is hard to believe that a sticking thermostat would cause all those electrical woes but am pretty sure you know more about it than I do. will let you know how it goes later this week, thanks again.

HipHotRod

Brad, wouldnt a coolant temp sensor cause the flat line?

ChevyMgr

That is possible, a DVOM would be needed to test for a bad one. Or a person can do what a lot of owners do, and that is guess that is the problem and replace it. And if that doesn't work try the thermostat next. It takes around 45 minutes to replace the thermostat and less then 30 to do the temp sensor, so it's not a major thing if you wanted to try both of them. If we were in Vegas the odds would favor the thermostat, but sometimes the long shots win too.

2ofthemincali

a temp sensor would fail and stay bad but this keeps fixing itself. bought thermostat at Kragens for $30, came with o-ring. asked the dealer to point out the temp sensor but the gal who signs you in is clueless and you can't actually talk to a mechanic. will attempt install later this week. would resetting codes be what is bringing guage back to life? works for a week or so before it flat-lines again. thanks again for your help and I'll keep you posted on the results.