Service code PO128?

Service engine soon light came on my wifes 2000 Grand Prix GT yesterday.

My daughter took it to Autozone to see what code it spit out and she said they told her it was code PO128; coolant temp below thermostat regulating temp.

What the heck does that mean!! Is it running too cool?

Does it need a new thermostat or what?

Thanks for your help.

Sounds like the thermostat may be stuck open or has anyone put a colder thermostat in the car,because once it starts to get cold it will throw a SES with a colder then stock thermostat.


CLICK HERE (http://www.pfyc.com/supportfiles/tstat/tstat.htm) for instructions for changing out the thermostat

~Larry~

BIG-L

Thanks for the info!

I was told on another forum that it could also be a bad coolant temp. sensor.

If the new t-stat doesn't take care of the problem I guess I'll replace that too.

Where is it located on the engine?

My El Camino has one on the thermostat housing.

Man, this is deja-vu. My 2000 GT is doing the same thing. Once the engine light came on, I took it in to get read and they said it was reading that the engine wasn't getting warm enough and I need to get the engine thermometer replaced.

Before I get all involved in replacing my thermostat, do I need to change my anti-freeze or do anything else?

Nah, there's no reason replacing a thermostat would require you to exchange your coolant. If it has never been done before and looks dirty, it wouldn't be a bad idea, but not a requirement for a new 'stat.

I just read code P0128 from my grand prix GT too. It was 7 degrees that morning.

Can you believe the dealer wanted $80 to read the codes from my car? so I said screw that and went and bought an ODBii interface from scantool.net. It works great and now I will be checking my own codes and making my own repairs.

I'll clear this code, and if it comes back I'll probably try replacing the thermostat.

Good to see other people have the came car and are experiencing similar issues. At least this way I'll know what to expect on my car.