What it means
The control module monitors the radiator coolant temperature sensor circuit and sets this code when its signal is higher than the expected range. A high 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 lets the control module estimate radiator coolant temperature. P00B4 sets when the signal is higher than the expected range, which can happen if the signal circuit is open or pulled toward voltage; the code does not by itself identify the failed part.
Common causes
Most likely first.
- Signal wire open
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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 for an implausibly hot value, especially with a cold engine.
- Inspect the radiator sensor connector and harness for an open connection, corrosion, broken wires, or wiring pinched against a power source.
- Use the wiring diagram to test the signal circuit for an open or short to voltage, following the manufacturer's procedure.
- Check sensor reference, ground, and signal behavior against the manufacturer's specification to isolate the sensor from the harness.
- After repairs, clear the code and confirm the radiator temperature reading tracks plausibly through warm-up.
Common fixes
- Repair an open radiator coolant temperature sensor signal wire.
- Separate and repair wiring shorted to a battery or other voltage source.
- Clean or repair corroded or damaged connector pins.
- Replace the radiator coolant temperature sensor if it fails the specified test.
Can I keep driving?
A falsely high or unreliable reading may affect cooling-fan operation and temperature indication. Watch the gauge and stop if the engine overheats or the fan fails to control temperature.
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.