P00B4Radiator Coolant Temperature Sensor Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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).
- What you may notice
- Check engine light on
- Thermostat and coolant flow diagnostics are suspended
- Often no noticeable symptoms
- Likely causes
- LikelyConnector or wiring at the radiator corroded or damaged (exposed front position)
- LikelySensor open internally
- PossibleSignal wire broken or shorted to reference or battery voltage
- RareEngine control module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €60 – €150
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.