I've got a 2002 4WD auto blazer. Went to Auto Zone and was told my error code is P0128. They said probably coolant level. Coolant level looks good, heater works just fine and engine temp looks to be well within the normal range. Any help would be appreciated.

 

ok that means that your car is running below the temperature the thermostat is supposed toclose maybe the thermostat is stock open and it doesnt close when its supposed to or might be something else

 

So you're telling me it'seitherthe thermostat or something else???

 

Could be a bad PCM coolant temp sensor (engine coolant temp - ECT). There are different sensors for the gauge and the PCM. If the gauge on the dash shows proper engine temp, chances are the t-stat is fine.