P00B4 - Radiator Outlet Temperature Sensor Circuit High
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P00B4 is set when the Engine Control Module (ECM) detects a high voltage condition in the radiator outlet coolant temperature sensor circuit (Sensor 2). This sensor monitors the cooling efficiency of the radiator to manage electric cooling fan operation and thermostat diagnostics. Since most automotive temperature sensors are NTC (Negative Temperature Coefficient) thermistors, high voltage typically signifies an open circuit or high resistance in the wiring or the sensor itself.
Possible Causes
Faulty radiator outlet coolant temperature sensor (Sensor 2)
Open circuit or corrosion in the sensor wiring harness
Poor electrical connection or backed-out pins at the connector
Faulty thermostat causing irrational temperature readings
Internal ECM failure
Symptoms
Recommended Solution
- Visual Inspection: Check the sensor connector and wiring at the radiator outlet for signs of damage, corrosion, or pin tension issues.
- Voltage Test: Verify a 5V reference signal and a solid ground at the sensor connector with the ignition ON.
- Resistance Test: Measure the sensor's resistance. At 20°C (68°F), it typically measures 2k-3k Ohms. Infinite resistance indicates an open circuit.
- Live Data: Cross-reference Sensor 1 (Engine) and Sensor 2 (Radiator) on a cold engine. They should be nearly identical.
- Replacement: If wiring is intact but the sensor fails resistance tests, replace the radiator outlet temperature sensor.
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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