P00B4: Radiator Coolant Temperature Sensor Circuit High

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. P00B4 means the sensor resistance or signal voltage is very high, typically an open circuit or a short to the reference voltage; with an NTC sensor the control module then reads an extremely low temperature (around −60 °C in a documented case).

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 open internally
• Signal wire broken or shorted to reference or battery voltage
• 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. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
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 P00B4 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 0: Subsystem depends on the code range
• B4: Specific fault in that system

Frequently asked questions

Can I keep driving with code P00B4?

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 P00B4?

The most common causes are: connector or wiring at the radiator corroded or damaged (exposed front position); sensor open internally; signal wire broken or shorted to reference or battery voltage.

Related codes

• P00B1Radiator Coolant Temperature Sensor Circuit
• P00B2Radiator Coolant Temperature Sensor Circuit Range/Performance
• P00B3Radiator Coolant Temperature Sensor Circuit Low
• P00B5Radiator Coolant Temperature Sensor Circuit Intermittent/Erratic
• P0118Engine Coolant Temperature Sensor 1 Circuit High

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 16OBDG03 Engine Diagnostics
• gsi.ext.gm.com: 16OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 19OBDG03A Diagnostics

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.