Powertrain, generic · Fuel and air metering, auxiliary emission controls

P00B6 Radiator Coolant Temperature/Engine Coolant Temperature Correlation

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

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

Symptoms

  • Check engine light on
  • Usually no noticeable symptoms

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–200
Time0.5–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

radiator coolant temperature sensorengine coolant temperature sensorsensor wiring

Related codes

P00B2P00B3P00B4P0116P2181

References: law.cornell.edu, gsi.ext.gm.com, en.wikipedia.org.