P00B6: Radiator Coolant Temperature/Engine Coolant Temperature Correlation

What does P00B6 mean?

The radiator coolant temperature sensor is an NTC thermistor that measures coolant temperature on the radiator side, typically at the radiator outlet; the exact position depends on the manufacturer. Together with the engine coolant temperature sensor it gives a second measuring point, which the control module uses to diagnose the thermostat and coolant flow, for example on engines with an electrically heated map-controlled thermostat. After a long standstill (eight hours in a documented case) engine and radiator should be at the same temperature. P00B6 is set at the next start when the engine and radiator coolant temperature sensors differ by more than a threshold that may depend on intake air temperature. A detected engine block heater cancels the test. From this alone the control module cannot tell which sensor is wrong.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on
• Usually no noticeable symptoms

Common causes

• High Radiator coolant temperature sensor drifting
• High Engine coolant temperature sensor drifting
• Medium Contact resistance at a connector
• Medium Retrofitted engine preheater or auxiliary heater not detected by the system

Likelihood is a general estimate across vehicles; your make and model may differ.