P00B6: Radiator Coolant Temperature/Engine Coolant Temperature Correlation

What it means

The radiator coolant temperature and engine coolant temperature readings do not correlate as expected.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The control module compares radiator coolant temperature with engine coolant temperature to check whether the two readings agree as the engine warms and coolant circulates. P00B6 sets when the relationship between these sensors is implausible, which may reflect an inaccurate sensor, a circuit fault, or a thermostat that is not regulating temperature correctly.

Common causes

Most likely first.

1. Radiator coolant temperature sensor reading inaccurate
2. Engine coolant temperature sensor reading inaccurate
3. Loose, corroded, or damaged sensor connector
4. Open or shorted sensor wiring
5. Thermostat not regulating temperature correctly

Symptoms

• Check engine light on
• Cooling fan runs constantly or not at all
• Cabin heater weak or excessively hot
• Possible long warm-up time or hard cold start

How to diagnose it

1. After the engine has cooled, record freeze-frame data and compare both coolant temperature readings with ambient temperature for an implausible mismatch.
2. Watch radiator and engine coolant temperatures together from a cold start through warm-up to see when their relationship becomes unexpected.
3. Inspect both named sensor connectors and wiring for corrosion, loose pins, open circuits, shorts, or damage.
4. Check thermostat behavior and coolant circulation if both sensor readings appear plausible individually but warm-up or temperature changes are abnormal.
5. Test each sensor and its circuit against the manufacturer's specification to identify which reading is inaccurate.

Common fixes

• Repair loose, corroded, or damaged wiring at the radiator or engine coolant temperature sensor.
• Replace the sensor that fails the manufacturer's test.
• Replace a thermostat that does not regulate engine warm-up correctly.
• Repair a verified control module circuit fault after checking both sensors and their wiring.

Can I keep driving?

The mismatch can accompany poor fan control, weak cabin heat, or abnormal engine temperature. Monitor the gauge and stop if the engine overheats; continued overheating can damage the engine.