P0128 Jeep - eng light On when running A/C. Operates normal No light with A/C off.

Question

Jeep Compass 2005
I can use the car for long a time with no light On as long as I do not use air conditioned.
Soon after running A/C light comes On and activates code P0128
Hot weather most of the time but never even close to freezing point.

Answer 1

P0128 Coolant thermostat malfunction

This code then is more of a open thermostat. the fix replace the thermostat and replaenish the coolant

 Most P0128 codes are resolved when the thermostat is replaced.