P0128 fault code: what it means

P0128: Coolant stays below thermostat temperature for too long after start-up. Nearly always a thermostat stuck open.

Engine and gearbox (powertrain) · Minor

Usual causes, most likely first

thermostat stuck open
low coolant level
faulty coolant temperature sensor
cooling fan running all the time

P0128 by make

BMW

Engine not reaching thermostat temperature. Common on BMW with the map-controlled (electric) thermostat stuck open.

Usual causes: thermostat stuck open; coolant temperature sensor; low coolant

Honda

Engine is not warming up to thermostat temperature in time. Very common on Civic and CR-V, usually a sticking thermostat.

Usual causes: thermostat stuck open; low coolant; coolant temperature sensor

Hyundai

Engine taking too long to reach normal temperature.

Usual causes: thermostat stuck open; ECM software needing an update (Hyundai TSB on 2016-18 Tucson); faulty coolant temperature sensor; low coolant

Isuzu

Engine slow to reach temperature.

Usual causes: thermostat stuck open; low coolant; coolant temp sensor

Jeep

Engine takes too long to reach temperature. Usually a thermostat stuck open.

Usual causes: thermostat stuck open; coolant temperature sensor; low coolant

Kia

Engine taking too long to reach normal temperature.

Usual causes: thermostat stuck open; faulty coolant temperature sensor; low coolant

Mercedes-Benz

Coolant taking too long to reach working temperature. On Mercedes almost always the thermostat stuck open.

Usual causes: thermostat stuck open; faulty coolant temperature sensor

Mini

Engine not reaching thermostat temperature in time. Usually the thermostat stuck open.

Usual causes: thermostat stuck open; coolant temperature sensor; low coolant

Mitsubishi

Engine not reaching normal temperature in time.

Usual causes: thermostat stuck open; low coolant; faulty coolant temperature sensor

Subaru

Engine is not reaching normal temperature in time. Very common on FB25 (2011-2018 Forester etc.); on Subaru it can also switch off EyeSight.

Usual causes: thermostat stuck open (updated Subaru part available); wrong-temperature thermostat fitted; low coolant; faulty coolant temperature sensor

Toyota

Engine coolant not reaching thermostat temperature in time after a start.

Usual causes: thermostat stuck open; faulty coolant temperature sensor; cooling fan running all the time; low coolant

Volvo

Engine slow to reach temperature.

Usual causes: thermostat stuck open; coolant temperature sensor; low coolant

What the repair usually costs

Radiator cooling fan motor or fan assemblyNZ$350–NZ$1,280 · A$330–A$1,210
Hybrid battery cooling fan and duct clean (Prius / Aqua / Corolla)NZ$100–NZ$240 · A$110–A$260
Hybrid battery cooling fan and duct clean (Camry / RAV4 / Estima / Lexus)NZ$140–NZ$320 · A$150–A$350
Hybrid battery cooling fan motor replaceNZ$210–NZ$650 · A$220–A$660

Not sure what P0128 means on your car? Ask Credov.

Before you clear it

Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.

Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.