What Does P00B3 Mean?
The radiator coolant temperature (RCT) sensor is reporting a voltage below the expected range, which the ECM interprets as an extremely high or out-of-range coolant temperature at the radiator outlet. This sensor is separate from the engine coolant temperature (ECT) sensor and monitors coolant temperature specifically at or near the radiator. The driver may notice the cooling fans running constantly, poor fuel economy, or the engine running rich due to incorrect coolant temperature data being fed to the PCM.
Common Causes
35%
Faulty radiator coolant temperature sensor (internal short or drift)
25%
Wiring short to ground in the RCT sensor circuit
20%
Corroded or damaged connector at the RCT sensor
10%
PCM internal fault or ground circuit issue
10%
Coolant contamination affecting sensor readings
Diagnostic Steps
1
Monitor the RCT sensor PID in live data — compare to the ECT sensor reading; at cold start both should be within a few degrees of ambient temperature.
2
Unplug the RCT sensor connector and check for voltage at the signal wire — you should see approximately 5V reference; if 0V, trace the wiring for a short to ground.
3
Measure the resistance across the RCT sensor terminals at known temperature — compare to the manufacturer's resistance-vs-temperature chart (typically ~2.5 kΩ at 68°F / 20°C for an NTC thermistor).
4
Inspect the sensor connector for corrosion, bent pins, moisture intrusion, or green oxidation on terminals.
5
If wiring and sensor test good, swap with a known-good sensor and re-test; if code persists, suspect PCM driver circuit.
Estimated Repair Cost
$40 - $200
Parts + labor, varies by vehicle and location
The radiator coolant temperature (RCT) sensor is reporting a voltage below the expected range, which the ECM interprets as an extremely high or out-of-range coolant temperature at the radiator outlet. This sensor is separate from the engine coolant temperature (ECT) sensor and monitors coolant tempe...
The most common cause of P00B3 (Radiator Coolant Temperature Sensor Circuit Low) is: Faulty radiator coolant temperature sensor (internal short or drift)
Typical repair costs for P00B3 range from $40 to $200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Generally safe to continue driving short distances. The PCM may default to a failsafe cooling strategy (fans running high), but the engine is not at immediate risk of overheating unless the actual coolant temperature is truly elevated. Monitor the actual engine temperature gauge closely.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P00B3 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Cooling System
Difficulty
Type
Generic (SAE)
Recommended Tools
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