Coolant thermostat temperature below regulating temperature

What the code means

The engine did not reach the modeled operating temperature in the expected time.

Severity and driving

Service soon; stop if actual overheating occurs

Plausible causes

Thermostat stuck open
Coolant-temperature sensor bias
Low coolant from a leak
Extreme conditions or cooling-fan control

Next checks

Never open a hot cooling system
Compare scan temperature with actual cold-soak temperature
Inspect for visible leakage only when fully cool

Source and boundary

Code structure follows SAE J2012. Manufacturer-specific definitions, pinpoint tests, wiring, torque, fluids, and repair procedures require authoritative information for the exact vehicle.

SAE J2012 Diagnostic Trouble Code DefinitionsReviewed 2026-08-13

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