P0128 GMC Engine Coolant Temperature Below Thermostat Regulating Temperature

Possible causes

– Leaking or stuck open thermostat
– Low engine coolant level
– Insufficient warm up time
– Faulty engine coolant temperature sensor
– Engine coolant temperature sensor harness is open or shorted
– Engine coolant temperature sensor circuit poor electrical connection

Tech description

If cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem.

When is the obd code mean?

If the Powertrain Control Module (PCM) detects the calibrated amount of air flow and engine run time have been met, and the Engine Coolant Temperature (ECT) has not met the minimum thermostat regulating temperature, the code P0128 will set.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0128 GMC OBD Code Description