What Does P00B1 Mean?
The PCM has detected a general circuit malfunction with the radiator coolant temperature sensor. This sensor is separate from the engine coolant temperature (ECT) sensor and is typically located at the radiator outlet or in the lower radiator hose to measure the temperature of coolant leaving the radiator. The PCM uses this to evaluate cooling system efficiency. A circuit fault means the PCM cannot compare radiator outlet temperature to engine temperature, potentially missing cooling system problems.
Common Causes
35%
Failed radiator coolant temperature sensor (open or shorted thermistor)
25%
Damaged or corroded wiring in the sensor circuit
20%
Poor connector contact due to corrosion or loose fit
12%
Missing or faulty 5V reference voltage to the sensor
8%
PCM internal fault on the radiator temperature sensor input
Diagnostic Steps
1
Read the radiator coolant temperature PID and compare to the engine coolant temperature PID with the engine cold (after overnight soak) — both should read near ambient. Large discrepancies point to a sensor fault.
2
Disconnect the radiator coolant temperature sensor and measure resistance across the terminals — typical NTC thermistor reads 2–3 kΩ at 68°F/20°C. OL indicates open; near 0 Ω indicates a short.
3
With the sensor unplugged and key on, verify 5V reference voltage is present at the harness-side signal pin. If absent, check the 5V reference circuit for faults.
4
Inspect the sensor connector for coolant contamination, corrosion, or physical damage — the radiator area is subject to road spray, thermal cycling, and stone impacts.
5
Check the ground circuit by measuring voltage drop from the sensor ground pin to battery negative (should be less than 100 mV under load).
Estimated Repair Cost
$50 - $250
Parts + labor, varies by vehicle and location
The PCM has detected a general circuit malfunction with the radiator coolant temperature sensor. This sensor is separate from the engine coolant temperature (ECT) sensor and is typically located at the radiator outlet or in the lower radiator hose to measure the temperature of coolant leaving the ra...
The most common cause of P00B1 (Radiator Coolant Temperature Sensor Circuit) is: Failed radiator coolant temperature sensor (open or shorted thermistor)
Typical repair costs for P00B1 range from $50 to $250, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Driving is generally safe if the engine coolant temperature (ECT) sensor is functioning correctly. However, the PCM loses the ability to detect reduced radiator cooling efficiency, which means an overheating condition could develop without adequate warning. Monitor the temperature gauge and repair promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P00B1 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Engine Cooling System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
