P00B3 - Radiator Coolant Temperature Sensor 2 Circuit Low
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P00B3 is set when the Engine Control Unit (ECU) detects a voltage signal from the Engine Coolant Temperature Sensor 2 (ECT 2) that is below the calibrated limit (typically below 0.2V). The sensor is an NTC thermistor, where resistance drops as temperature rises. A 'Circuit Low' condition usually signifies a short circuit to ground in the signal wire or a sensor failure with abnormally low internal resistance. ECT 2 is typically located at the radiator outlet to monitor radiator efficiency and manage cooling fan duty-cycles.
Possible Causes
Signal wire shorted to ground in the ECT 2 circuit
Faulty Radiator Coolant Temperature Sensor 2 (internal short)
Corroded or damaged connector at the sensor
Internal Engine Control Unit (ECU) fault
Symptoms
Recommended Solution
- Visual Inspection: Check wiring and connector at ECT sensor 2 (usually near radiator outlet) for chafing or corrosion.
- Measurement (Multimeter): Disconnect the sensor. With ignition ON, check for 5V reference voltage on the signal wire. Check if the signal wire has continuity to ground (indicating a short).
- Component Test: Measure resistance across sensor pins. At 20°C (68°F), it should be approx 2000-3000 Ohms. A reading near 0 Ohms confirms an internal short.
- Advanced Diagnosis: Use a scan tool to monitor ECT 2 live data. If it shows max temperature (e.g., 150°C/300°F) constantly, the circuit is shorted.
- Repair: Replace the sensor if resistance is out of spec, or repair wiring harness.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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