P00B1
Radiator Coolant Temperature Sensor Circuit
Engine cooling / temp sensor
Generic OBD-II
High
What it means
P00B1 means the ECM has detected a problem in the radiator coolant temperature sensor circuit — the sensor that monitors coolant temperature at the radiator (separate from the main engine coolant temp sensor). The ECM uses it to manage the cooling fans, so a fault can lead to fans running when they shouldn't, not running when they should, and inaccurate temperature readings.
High
Can I keep driving? Usually yes, but watch your temperature gauge — this sensor helps control the cooling fans, so a fault can affect fan operation and risk overheating.
Common symptoms
What you'll notice
- Check-engine light on
- Cooling fans running constantly or not coming on at all
- Temperature gauge reading erratically or inaccurately
- Engine running warmer than normal in traffic
Common causes
Most likely first
- Faulty radiator coolant temperature sensorLikely
- Open or shorted wiring in the sensor circuitCommon
- Corroded or loose sensor connectorCommon
- Failed ECM/PCM (rare)Less often
How to diagnose & fix
Work through it in order
- Read the radiator coolant temp sensor value on a scan tool and compare it to the engine coolant temp (ECT) sensor — a cold engine should read close to ambient.
- Inspect the sensor connector and wiring for corrosion, damage, or a loose pin.
- Measure sensor resistance/voltage against spec and back-probe the circuit for opens or shorts.
- Replace the radiator coolant temperature sensor if it's out of range. Clear and re-test, confirming fan operation.
FAQ
Quick answers
Is it safe to drive with P00B1?+
Short trips usually, but keep an eye on the temperature gauge. Because this sensor helps trigger the cooling fans, a fault can let the engine overheat — pull over if it climbs into the red.
Can I just clear P00B1?+
It will come back once the ECM rechecks the circuit. Fix the sensor or wiring first, especially since it ties into cooling-fan control.
Related codes
Often seen with P00B1
Read & clear P00B1 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