P00B5: Radiator Coolant Temperature Sensor Circuit Intermittent/Erratic

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. P00B5 is set when the signal jumps or drops out briefly, which typically points to a loose contact. No manufacturer description naming this exact code was found.

Symptoms

• Check engine light on
• Thermostat and coolant flow diagnostics are suspended
• Often no noticeable symptoms

Most likely causes

• Connector or wiring at the radiator corroded or damaged (exposed front position)
• Sensor faulty
• Loose contact in the circuit
• Engine control module faulty

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. Gently move the wiring with the engine running and watch whether the reading changes.
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: easy
• It affects emissions.

What each character of P00B5 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 0: Subsystem depends on the code range
• B5: Specific fault in that system

Frequently asked questions

Can I keep driving with code P00B5?

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 P00B5?

The most common causes are: connector or wiring at the radiator corroded or damaged (exposed front position); sensor faulty; loose contact in the circuit.

Related codes

• P00B1Radiator Coolant Temperature Sensor Circuit
• P00B2Radiator Coolant Temperature Sensor Circuit Range/Performance
• P00B3Radiator Coolant Temperature Sensor Circuit Low
• P00B4Radiator Coolant Temperature Sensor Circuit High
• P0119Engine Coolant Temperature Sensor 1 Circuit Intermittent/Erratic

Sources

• law.cornell.edu: 13 CCR 1968.2
• en.wikipedia.org: Thermistor
• en.wikipedia.org: Radiator (engine cooling)

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.