Cooling

P00B3 — Radiator Coolant Temperature Sensor Circuit Low

Severity: medium Drive with care, to a shop

What P00B3 means

The engine computer reads coolant temperature at the radiator from the voltage of a thermistor-type sensor. P00B3 sets when that signal voltage drops below the expected range, which the computer interprets as an extremely hot reading. Typical causes are a failed sensor, a signal wire shorted to ground, or a bad connector.

Symptoms

  • Check engine light on
  • Erratic or implausible coolant temperature readings
  • Hard cold starts and rough idle
  • Poor fuel economy
  • Cooling fans running constantly or at the wrong time
  • Reduced engine performance

Possible causes

  1. Failed radiator coolant temperature sensor (internal short)
  2. Chafed wiring with the signal wire shorted to ground
  3. Corroded connector or damaged terminals at the sensor
  4. Water or coolant inside the connector
  5. PCM fault (unlikely)

How to diagnose

  1. Scan for codes and freeze-frame data and look for other temperature or fan codes
  2. Compare scan tool coolant temperature with an infrared thermometer reading on a cold engine
  3. Inspect the sensor connector and harness for corrosion, moisture, chafing and coolant residue
  4. Unplug the sensor: if the reading changes to an open-circuit (low temperature) value, the sensor is likely bad
  5. Measure sensor resistance and compare to specs at several temperatures
  6. Check for reference voltage (usually about 5 V) at the connector and for a signal short to ground
  7. Test the wires back to the PCM for opens and shorts
  8. If the wiring and sensor are good, inspect the PCM and its connectors

Common fixes

  • Replace the radiator coolant temperature sensor
  • Repair or replace the damaged wiring harness
  • Clean or replace the connector and terminals
  • Reflash or replace the PCM (rare)

Questions and answers

What does P00B3 mean?

The PCM detected low voltage in the radiator coolant temperature sensor circuit. The most common causes are a bad sensor or a short in the wiring.

Can I drive with P00B3?

You can for a short time with care, but the PCM is using wrong temperature data, which can lead to overheating and poor economy. Fix it as soon as you can.

How do I tell a bad sensor from a wiring problem?

Unplug the sensor connector. If the scan tool then shows an extreme cold or open-circuit reading, the wiring to the PCM is intact and the sensor is at fault. If nothing changes, look for a short to ground in the harness.

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.