Insufficient Coolant Temperature for Stable Operation

You can drive short distances. The engine will not overheat -- the problem is the opposite. It runs too cool, which wastes fuel and prevents the emission systems from working efficiently.

A thermostat replacement typically costs $100 to $250 total. The thermostat itself is $20 to $60, and labor is $50 to $150 depending on its location. Some thermostats are easy to access, while others are buried under intake components.

No, never remove the thermostat without replacing it. Running without a thermostat causes the engine to run too cool permanently, wasting fuel, increasing wear, and preventing the emission control systems from functioning properly.

California's OBD II regulation requires a thermostat malfunction to be flagged if, within an approved time after engine start, the coolant either fails to reach the highest temperature the OBD system needs in order to run its other diagnostics, or fails to come within 20 degrees Fahrenheit of the manufacturer's nominal thermostat regulating temperature (Title 13 CCR 1968.2, section (e)(10.2.1)). The first condition is why this code often appears alongside monitors that will not complete: the engine never gets warm enough for them to run. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.