DTC P0128: Engine Coolant Thermostat: Description

WARNING: This page is about a different car, the 2002 Pontiac Sunfire, 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

Engine Coolant Temperature (ECT) sensor monitors temperature of coolant. This input is used by PCM for engine control, and as an enabling criteria for some diagnostics.

Air flow coming into engine is accumulated and used to determine if engine has been driven within conditions that would allow engine coolant to heat up normally to thermostat regulating temperature. If coolant temperature does not increase normally, or does not reach regulating temperature of thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.

DTC will only run once per ignition cycle within enabling conditions.

If engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, DTC will set.