DTC P0126: Coolant Thermostat Stuck Open: Condition
WARNING: This page is about a different car, the 2002 Mazda 626. 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 (ECT) sensor readings when engine is first started and minimum intake air temperature is less than 6°C, and ECT sensor readings never exceeds 160°F (71°C). In setting DTC, Powertrain Control Module (PCM) is concluding that coolant thermostat is stuck open. This is a continuous monitor. MIL is illuminated when PCM detects malfunction during 2 consecutive drive cycles. Possible causes are:
- Coolant thermostat malfunction.
- Engine cooling fan malfunction.
- ECT sensor malfunction.
- PCM malfunction.