Cooling

P00B4 — Radiator Coolant Temperature Sensor Circuit High

Severity: medium Drive with care, to a shop

What P00B4 means

The PCM sends a reference voltage to the radiator coolant temperature sensor and reads the voltage drop to work out temperature. P00B4 sets when the signal stays above the expected range. This usually points to an open circuit, a poor connection or a failed sensor. The PCM then has unreliable data about coolant temperature at the radiator outlet.

Symptoms

  • Check Engine light on
  • Hard cold starts
  • Rough or erratic idle
  • Engine stalling
  • Poor fuel economy
  • Fluctuating or false temperature readings
  • Cooling fans behaving abnormally

Possible causes

  1. Failed radiator coolant temperature sensor
  2. Open circuit or high resistance in the wiring harness
  3. Corroded or loose sensor connector
  4. Open or poor ground at the sensor
  5. PCM fault (uncommon)

How to diagnose

  1. Scan for codes and freeze frame data, clear the code and see whether it returns.
  2. Inspect the sensor, connector and harness for damage, corrosion and chafing.
  3. Compare this sensor's scan tool reading with other coolant temperature sensors on a cold engine.
  4. Unplug the sensor: if the reading goes to the extreme value, the wiring back to the PCM is likely fine.
  5. Measure sensor resistance and compare it to the manufacturer's chart at a known temperature.
  6. Check reference voltage and ground at the connector with a multimeter.
  7. Test the harness from the sensor to the PCM for opens and high resistance.
  8. If wiring and sensor are good, evaluate the PCM.

Common fixes

  • Replace the sensor with an OEM-spec part
  • Repair or replace the damaged wiring section
  • Clean the connector terminals and secure the connector
  • Replace or reprogram the PCM if confirmed faulty

Questions and answers

What does P00B4 mean?

The PCM detected a high voltage signal in the radiator coolant temperature sensor circuit. The usual culprits are the sensor, a broken wire or a poor connector contact.

Can I drive with P00B4?

Only for short trips while watching the temperature gauge. The fans may not run correctly, so overheating is a risk.

How do I fix P00B4?

Check the connector and wiring first, then test the sensor resistance. Cleaning the connector, repairing the harness or replacing the sensor fixes most cases.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.