2010 HHR w/ 2.2L and about 88k miles. Within the last month, the ESC light and check engine light keep popping up. I ran the codes using an inexpensive code reader and got the P0302 code. I changed the plugs and it ran great... the lights came back and I got the same code. I've been able to isolate the situation that triggers the lights. It seems to happen whenever the car is in park and idling for more than 5 minutes or so. I can drive the car for days and the lights never come on, but the minute it is idling in park for an extended period of time, the dash lights up like a Christmas tree! In searching the internet, it seems that it could be a multitude of sensors that are causing the problem and I would really like to avoid throwing a bunch of money at it replacing things that don't need to be. The car runs fine despite the warning lights, but it's my wife's car, so just leaving it be is not an option.

Any thoughts or advice would be greatly appreciated.

 

Has coolant been disappearing? Does it get checked regularly?

What is the coolant temp when this happens?

What did spark plug #2 look like when you removed it.

P0302 means cyl #2 is misfiring. After new plugs is it still P0302?

Switch 2 of the coil packs, does the misfire move?

 

Thanks for the response. I did have to add some coolant with the last oil change, but it wasn't a huge amount. I've never noticed it running or smelling hot. What is your thinking with the coolant level / temp? All 4 plugs looked pretty good, and I got the same P0302 misfire code after they were changed. I had considered moving the coil packs to see if the code changed cylinders, so I guess I'll have to give that a shot. What's confusing me is that its the ESC that is coding first and then the check engine soon thereafter.

 

Coolant leaking into a cylinder can cause a misfire. If #2 was suspiciously clean or dirty that could be a clue.

The ESC is caused by the misfire, the misfire won't cause the CEL until it happens twice.

After the coil switch next test is compression and leakdown, looking for head gasket leaks or burned valves.

 

Swap the coils # 2 and #4 let us know if the code changes the P0304.

 

It's been a while... I swapped the coils, still get the same code. Checked the resistance of fuel injectors and all were consistent. Despite that reading, I tried changing the #2 injector and the car ran worse, so I reinstalled the old injector. In changing the oil, no sign of coolant leaking into oil. How likely is it that it's related to a sensor? Would low compression be the more likely cause? I'm hoping to avoid leakdown testing if possible; might be a little beyond my ability. Thanks

 

Compression test is easy. Just plug the tester into the spark plug holes and crank the engine. There are lots on youtube, nothing special with the HHR.

Leak down: https://www.chevyhhr.net/forums/how-...-engine-56053/

 

Yep, compression test is easy, and will tell you if you have a mechanical problem in the cylinder. If you do, then you will need to do a leak down test to determine what exactly the problem is.