P00B6: Radiator Coolant Temperature/Engine Coolant Temperature Correlation

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. After a long standstill (eight hours in a documented case) engine and radiator should be at the same temperature. P00B6 is set at the next start when the engine and radiator coolant temperature sensors differ by more than a threshold that may depend on intake air temperature. A detected engine block heater cancels the test. From this alone the control module cannot tell which sensor is wrong.

Symptoms

• Check engine light on
• Usually no noticeable symptoms

Most likely causes

• Radiator coolant temperature sensor drifting
• Engine coolant temperature sensor drifting
• Contact resistance at a connector
• Retrofitted engine preheater or auxiliary heater not detected by the system

What to check, in order

Start with the simplest. You can tick off each step.

1. With the engine cold, check the coolant level; never do this when the system is hot
2. Compare both signals at the same time in live data and check any recent installation work.
3. Check the actual temperature in live data
4. Make sure the fan comes on when it should
5. Check the thermostat and connector
6. Measure the sensor and replace it if its readings do not make sense

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P00B6 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 0: Subsystem depends on the code range
• B6: Specific fault in that system

Frequently asked questions

Can I keep driving with code P00B6?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P00B6?

The most common causes are: radiator coolant temperature sensor drifting; engine coolant temperature sensor drifting; contact resistance at a connector.

Related codes

• P00B2Radiator Coolant Temperature Sensor Circuit Range/Performance
• P00B3Radiator Coolant Temperature Sensor Circuit Low
• P00B4Radiator Coolant Temperature Sensor Circuit High
• P0116Engine Coolant Temperature Sensor 1 Circuit Range/Performance
• P2181Cooling System Performance

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 16OBDG03 Engine Diagnostics
• en.wikipedia.org: Thermistor

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.