Cooling system codes

Thermostat and coolant-temperature faults — engines that never warm up, weak cabin heat, poor economy.

Important: Content here is general information only, not professional mechanical advice or a diagnosis for a specific vehicle. When in doubt, have a qualified mechanic assess it promptly.

P0128: Coolant Temperature Below Thermostat Regulating Temperature — The engine is not reaching its normal operating temperature within the expected time — the coolant is staying cooler than the thermostat is designed to allow.