Unsticking Mazda thermostat

April 23, 2024
This bulletin applies to 2019-2022 Mazda3 and 2018-2021 Mazda6 vehicles.

This bulletin applies to 2019-2022 Mazda3 and 2018-2021 Mazda6 vehicles.

Some customers may experience the check engine light on with DTC P0126:00 (thermostat stuck open) and one or more of the following symptoms:

- The engine takes longer to warm up

- Engine temperature gauge fluctuates

- The low coolant temperature blue indicator light stays on longer or comes on while driving

- Poor heater performance, especially at idle

Note this does not apply to vehicles with SKYACTIV-G 2.5T.

Due to the production variety of the failsafe thermostat integrated into the coolant control valve, engine coolant may enter into a dry hollow in the failsafe thermostat, resulting in the unintended opening of the thermostat at lower temperatures (104-176 degrees Fahrenheit). To eliminate the concern, the production process of the coolant control valve has been modified.

1. Verify the concern and check the coolant temperature in the freeze frame data. If it is at around 104-176 degrees Fahrenheit, proceed to step two.

2. Replace the coolant control valve. P/N PYFD-15-16ZA for A/T; PYFA-15-16ZB for M/T.

3. Warm up the engine and confirm that the primary malfunction is resolved.

About the Author

Motor Age Staff

Motor Age has been publishing technical content for professional automotive technicians since 1899. Our writers have decades of experience and scores of ASE certifications, and they continue to teach new generations of technicians via classrooms all around the globe, as well as through the books and training manuals they've authored. 

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