P00B3

What it means

P00B3 is the generic code for a low signal from the radiator coolant temperature sensor circuit. The control unit saw the sensor's signal voltage fall below the expected range, which it reads as a short to ground or a sensor fault. This sensor is separate from the engine coolant temperature sensor, and its use varies by vehicle and engine.

Symptoms

• Engine warning light on
• Cooling fan running constantly or at the wrong times
• Erratic or incorrect temperature readings on a scan tool
• Poor fuel economy or rough running if the control unit relies on the reading
• Possible reduced performance if a default value is being used

Possible causes

• Faulty radiator coolant temperature sensor with an internal shortlikely
• Sensor signal wire chafed and shorted to earthlikely
• Water ingress, corrosion or damaged pins in the sensor connectorpossible
• Damaged wiring harness between the sensor and control unit, for example by heat or rubbingpossible
• Fault in the sensor reference voltage supply or earthrare
• Faulty control unitrare

How to diagnose

1. Read and record the stored codes and freeze frame data, noting engine temperature and load when the fault set
2. Check for other coolant temperature or cooling fan codes that could point to a shared wiring or supply fault
3. Compare the radiator coolant temperature reading with the engine coolant temperature reading on a cold engine; they should be close
4. Visually inspect the sensor, connector and wiring for chafing, heat damage, corrosion and coolant leaks
5. Unplug the sensor with the ignition on and watch the live reading; it should move to the open-circuit default, and if it stays low, suspect a wiring short to earth
6. Measure the sensor resistance and compare it with the manufacturer's temperature-resistance specification, as values depend on the model
7. Check the reference voltage and earth at the connector and test the signal wire for continuity and short to earth
8. Check the cooling system level and condition, since the sensor must be in contact with coolant to read correctly

How to fix

• Replace the radiator coolant temperature sensor if its resistance is out of specification
• Repair or replace the damaged wiring section that is shorting to earth
• Clean or replace the corroded or damaged connector terminals and ensure the connector is sealed
• Restore the reference voltage or earth supply if a fault is found in that circuit
• Top up or refill the coolant to the correct specification if the level was low, and fix any leak found
• Diagnose and replace the control unit only after wiring and the sensor have been proven good

Can I keep driving?

Nearby codes

• P00B2GenericRadiator Coolant Temperature Sensor Circuit Range/Performance
• P00B4GenericRadiator Coolant Temperature Sensor Circuit High