P00B4
Radiator Coolant Temperature Sensor Circuit High
Engine cooling
Generic OBD-II
High
What it means
P00B4 means the signal from the radiator coolant temperature sensor is too high, which almost always indicates an open circuit or a disconnected sensor so the computer reads the coolant as unrealistically cold. Because this sensor helps control the cooling fans, the fault can lead to poor fan behavior and, in the worst case, overheating.
High
Can I keep driving? The engine still runs, but the computer has lost a valid radiator-temperature reading, so cooling-fan control may be off — watch the temperature gauge and avoid hard driving until fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Cooling fans running constantly or not turning on when they should
- Temperature reading that seems stuck cold or implausible
- Possible overheating if the fans don't engage in traffic
Common causes
Most likely first
- Open circuit or high resistance in the radiator coolant temperature sensor wiringLikely
- Disconnected or failed radiator coolant temperature sensor (reads as very cold)Common
- Corroded or loose sensor connectorCommon
- Damaged harness or poor ground in the sensor circuitLess often
- Rarely, an ECM/PCM faultLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the reported temperature is unrealistically low (the 'high' voltage signal an open circuit produces).
- Inspect the radiator coolant temperature sensor connector for corrosion, damage, or a loose fit.
- Check the signal and ground wires for opens and high resistance back to the ECM.
- Measure the sensor's resistance against spec; replace it if out of range.
- Repair any damaged wiring, then clear the code and confirm the fans cycle normally.
FAQ
Quick answers
Is it safe to drive with P00B4?+
Only briefly. The car will run, but the computer may not command the cooling fans correctly, which risks overheating in slow traffic. Keep an eye on the temperature gauge and get it fixed soon.
Can I just clear P00B4?+
It will come back until the sensor or its wiring is repaired. Because a 'circuit high' usually means an open or disconnected sensor, start with the connector and wiring.
Related codes
Often seen with P00B4
Read & clear P00B4 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX