Often, the intent of the P0128 code is to indicate a faulty thermostat (likely stuck in the open condition). Similar codes: P0125In determining that the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air ...
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) P0128 - GM Type Powertrain - Fuel and Air Metering - ISO/SAE Controlled Description ECT Below Thermostat Regulating Temperature Conditions Cause Engine running, ECT and IAT inputs from 14-97°F, then the PCM detected the...