What Does P00B4 Mean?
The radiator coolant temperature sensor circuit is reading a voltage higher than the expected range, which the ECM interprets as an extremely low or impossible coolant temperature at the radiator. This typically indicates an open circuit condition in the sensor or its wiring. The driver may notice poor cold-start performance, higher emissions, or the engine running rich because the PCM thinks the engine is colder than it actually is.
Common Causes
35%
Open circuit in the RCT sensor wiring (broken wire or disconnected connector)
30%
Faulty radiator coolant temperature sensor (open internally)
20%
Corroded or spread connector terminals causing high resistance
10%
Missing or damaged 5V reference from PCM
5%
Sensor not properly seated or cross-threaded in the radiator housing
Diagnostic Steps
1
Check live data for the RCT sensor PID — a high circuit code typically shows -40°F/-40°C, indicating the ECM sees maximum resistance (open circuit).
2
Inspect the RCT sensor connector for damage, corrosion, or being unplugged; re-seat the connector and re-check.
3
With the sensor unplugged, measure resistance across the sensor terminals — an open reading (OL/infinite) confirms a failed sensor; a normal NTC should read approximately 2.5 kΩ at 68°F.
4
Back-probe the signal wire at the PCM connector to verify continuity from the sensor — an open wire will show OL on the ohmmeter.
5
Verify the 5V reference is present at the sensor connector with the key on, engine off — if missing, check other sensors sharing the same 5V reference line.
Estimated Repair Cost
$40 - $200
Parts + labor, varies by vehicle and location
The radiator coolant temperature sensor circuit is reading a voltage higher than the expected range, which the ECM interprets as an extremely low or impossible coolant temperature at the radiator. This typically indicates an open circuit condition in the sensor or its wiring. The driver may notice p...
The most common cause of P00B4 (Radiator Coolant Temperature Sensor Circuit High) is: Open circuit in the RCT sensor wiring (broken wire or disconnected connector)
Typical repair costs for P00B4 range from $40 to $200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive short distances. The PCM will use a default value for the radiator coolant temperature, which may cause slightly richer fuel mixture and higher fuel consumption. The engine cooling fans may not operate optimally. Monitor the engine temperature gauge and avoid heavy load or towing until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P00B4 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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