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

P00B4 Radiator Coolant Temperature Sensor Circuit High

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. P00B4 means the sensor resistance or signal voltage is very high, typically an open circuit or a short to the reference voltage; with an NTC sensor the control module then reads an extremely low temperature (around −60 °C in a documented case).

Likely causes

Connector or wiring at the radiator corroded or damaged (exposed front position)
Sensor open internally
Signal wire broken or shorted to reference or battery voltage
Engine control module faulty

Symptoms

  • Check engine light on
  • Thermostat and coolant flow diagnostics are suspended
  • Often no noticeable symptoms

Repair estimate

DifficultyEasyDIY possible
Parts and labour€60–150
Time0.3–1 h

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

Parts involved

radiator coolant temperature sensorradiator coolant temperature sensor wiring

Related codes

P00B1P00B2P00B3P00B5P0118

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.