What it means
The control module monitors the radiator coolant temperature sensor circuit and sets this code when its signal is lower than the expected range. A low circuit signal does not by itself establish whether the cause is the sensor or its wiring.
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 signal is monitored by the control module to determine radiator coolant temperature. P00B3 sets when the circuit signal is lower than the module expects; a signal pulled toward ground or excessive resistance can cause this, but the code alone does not prove the sensor has failed.
Common causes
Most likely first.
- Signal wire shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Temperature gauge may read incorrectly or fluctuate
- Cooling fan may run unusually or not operate as expected
How to diagnose it
- Save freeze-frame data and check the scan-tool radiator temperature reading; a reading that is implausibly cold can support a low-signal fault.
- Inspect the radiator sensor connector and harness for corrosion, chafing, pin damage, or contact with ground.
- With the wiring diagram, check the signal circuit for a short to ground and inspect connector contact resistance using the manufacturer's procedure.
- Check the sensor and its reference and ground circuits against the manufacturer's specifications to distinguish a sensor fault from a harness fault.
- Repair the identified wiring or connector issue, then clear the code and confirm the radiator temperature reading responds plausibly.
Common fixes
- Repair signal wiring shorted to ground or chafed through its insulation.
- Clean or repair corroded connector pins and restore a sound connection.
- Replace the radiator coolant temperature sensor if it fails the specified test.
- Repair the control module circuit only after verifying the sensor and harness.
Can I keep driving?
The low signal can make the temperature display or fan control unreliable. Monitor for overheating and stop if the gauge rises above normal or coolant is visibly leaking.
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.