Cooling

P00B6 — Radiator and Engine Coolant Temperature Sensor Mismatch

Severity: medium Drive with care, to a shop

What P00B6 means

The engine control module compares the coolant temperature at the radiator outlet with the engine coolant temperature from the ECT sensor. Once the system is warm, the two readings should track each other closely. If the difference exceeds the allowed limit, the module sets P00B6 and turns on the check engine light. The cause can be a bad sensor or a real coolant flow problem.

Symptoms

  • Check engine light on
  • Erratic or illogical coolant temperature readings
  • Rough idle
  • Reduced fuel economy
  • Cooling fan running constantly
  • Possible engine overheating

Possible causes

  1. Faulty engine coolant temperature (ECT) sensor
  2. Faulty radiator coolant temperature (RCT) sensor
  3. Low coolant level or air trapped in the cooling system
  4. Open, shorted or corroded wiring and connectors at the sensors
  5. Stuck thermostat or poor coolant circulation
  6. Rarely, a PCM fault or software issue

How to diagnose

  1. Scan for all codes and freeze frame data, and look for other temperature-related codes
  2. Check coolant level and condition on a cold engine and look for leaks
  3. With a scan tool, compare ECT and RCT readings on a cold engine; they should be nearly the same
  4. Warm the engine and watch both readings rise, then compare with actual temperature using an infrared thermometer
  5. Inspect sensor connectors and wiring for corrosion, damage and loose pins
  6. Measure sensor resistance and compare to the manufacturer spec
  7. Check reference voltage and ground at the sensor connectors
  8. Test the thermostat and cooling fan operation

Common fixes

  • Replace the faulty ECT or RCT sensor
  • Repair wiring and clean or replace the connector
  • Top off or replace coolant and bleed air from the system
  • Replace a thermostat that sticks open or closed
  • Reflash or replace the PCM (rare)

Questions and answers

What does P00B6 mean?

The control module found that the radiator coolant temperature sensor and the engine coolant temperature sensor disagree by more than allowed. Either sensor, the wiring or the cooling system itself could be at fault.

Can I drive with code P00B6?

For a short distance, yes, if the gauge reads normal. Don't put off diagnosis, because real overheating can damage the cylinder head and head gasket.

Is replacing a sensor enough to fix it?

Not always. Check coolant level, trapped air, connectors and the thermostat first, otherwise a new sensor may not fix the cause.

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.