Hey guys, I've been getting the p0128 code on my hhr, and I'm thinking it's either a sticking thermostat or faulty connections somewhere. The car's temp barely makes it to 180, 179 being the highest (probably because we dont use it too much) even on the highway. The fan doesn't Come on until the AC is turned on, and I tried removing the connections to the coolant temp sensor and starting the car, to which the fan kept running constantly and the dashboard showed two dashes where the temp was supposed to show. I opened the pressure cap and checked for any movement of liquid in the pipe when the car was running, it was all very Stationary. How do I start troubleshooting this?

 

Replace the t-tat with a GM 131-158 no other part number!!!!! The t-stat's job is to keep the temp ABOVE 180F.
Strange thing here is that your AC is working?

 

X2 install one of those thermostats, and if you drain the coolant from the rad drain spigot, refill with fresh Dexcool 50/50 mix.

https://www.chevyhhr.net/forums/how-...l-p0128-24493/


don’t forget to burp the cooling system

https://www.chevyhhr.net/forums/how-...-system-60614/

 

Great News!! I replaced the thermostat and everything is back to as it should be, no error codes, and the temperature maintains 190-210 always.
Thanks a lot for the help.
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PS. My AC used to work even with the old, bad one. No difference now.

 

The AC Delco 131-158 opens at 180 degrees, did you install something different, you say 190 degrees to 210 degrees. Be ready to change to the correct thermostat

 

oh no it's the right one, I just meant the operating temperature because our place is mostly hot, so the temperature rarely falls below 190 once we hit the road (unless it's winter). The thermostat opens at 180 degrees perfectly.

 

Ok , that’s a relief! Thought maybe you when rogue at the parts palace, trying to save a couple of bucks.