What it means
The radiator coolant temperature sensor circuit signal is intermittent or erratic.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The radiator coolant temperature sensor provides a changing signal that the control module uses to assess radiator temperature. P00B5 sets when that signal drops out or changes erratically, often because vibration or movement interrupts contact at the connector or in the harness.
Common causes
Most likely first.
- Connector loose or corroded
- Connector with intermittent contact under vibration
- Harness routed against vibrating component
Symptoms
- Check engine light on
- Temperature gauge may fluctuate or read incorrectly
- Cooling fan may run intermittently or unusually
How to diagnose it
- Save freeze-frame data and any related codes, then use live data to see whether the radiator temperature reading jumps or cuts out.
- Inspect the radiator sensor connector for a loose fit, corrosion, damaged locking features, or pins that may lose contact under vibration.
- Follow the harness along its route and look for rubbing, tension, or contact with a vibrating or hot component.
- With the scan tool displaying radiator temperature, gently move the connector and harness to check for signal changes while following safe workshop practice.
- Test the sensor and circuit for intermittent continuity or contact faults using the manufacturer's procedure.
Common fixes
- Reseat and secure the radiator sensor connector.
- Clean or replace damaged connector terminals that lose contact.
- Repair and correctly route a chafed or vibrating harness section.
- Replace the radiator coolant temperature sensor if its output is intermittent during testing.
Can I keep driving?
Intermittent readings can make the temperature display or cooling fan behave unpredictably. Keep an eye on engine temperature and stop if it rises above normal.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.