DTC P0126: Coolant Thermostat Stuck Open: Condition
WARNING: This page is about a different car, the 2002 Mazda Protege5 and 2002 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.
DTC is set when:
- Vehicle speed is more than 5.9 MPH.
- Intake air temperature is more than 14°F (-10°C).
- Difference between engine coolant temperature and minimum intake air temperature readings is less than 6°C when engine is first started.
- ECT sensor readings never exceeds 160°F (71°C).
In setting DTC, PCM is concluding that coolant thermostat is stuck open. This is an intermittent monitor. MIL is illuminated when PCM detects malfunction during 2 consecutive drive cycles. Possible causes are:
- Coolant thermostat malfunction.
- ECT sensor malfunction.
- PCM malfunction.