What Does P00B6 Mean?
The PCM has detected that the radiator coolant temperature (RCT) sensor and the engine coolant temperature (ECT) sensor are not reading within an acceptable range of each other under conditions where they should agree. After the engine has been sitting long enough to reach thermal equilibrium, both sensors should read near ambient temperature; during operation, the RCT should read lower than ECT. This code indicates a disagreement that exceeds the calibrated threshold, suggesting one sensor is inaccurate or the cooling system has a flow problem.
Common Causes
30%
Faulty radiator coolant temperature sensor reading incorrectly
25%
Faulty engine coolant temperature sensor reading incorrectly
25%
Stuck thermostat preventing proper coolant flow through the radiator
10%
Low coolant level causing air pockets around one sensor
10%
Restricted radiator or clogged coolant passages
Diagnostic Steps
1
Compare both the ECT and RCT PIDs on a cold start — both should read within 5°F of ambient temperature; a sensor showing a significant offset at cold soak is likely faulty.
2
Run the engine to operating temperature and monitor both sensor PIDs — the ECT should stabilize around 190-220°F and the RCT should read lower (typically 20-50°F less); if both read identically or RCT reads higher, suspect a thermostat issue.
3
Check coolant level in the radiator (cold engine) and the reservoir — low coolant can cause one sensor to be exposed to air instead of liquid coolant.
4
Use an infrared thermometer to independently verify the temperature at both sensor locations and compare to the PID readings to identify which sensor is lying.
5
If both sensors read correctly against the IR thermometer, inspect the thermostat operation by feeling the upper radiator hose — it should get hot after the thermostat opens around 195°F.
Estimated Repair Cost
$50 - $350
Parts + labor, varies by vehicle and location
The PCM has detected that the radiator coolant temperature (RCT) sensor and the engine coolant temperature (ECT) sensor are not reading within an acceptable range of each other under conditions where they should agree. After the engine has been sitting long enough to reach thermal equilibrium, both ...
The most common cause of P00B6 (Radiator Coolant Temperature/Engine Coolant Temperature Correlation) is: Faulty radiator coolant temperature sensor reading incorrectly
Typical repair costs for P00B6 range from $50 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with caution and monitor the engine temperature gauge. If the correlation issue stems from a stuck thermostat, the engine could overheat, leading to head gasket failure or engine damage. If only a sensor is off, the risk is lower but the PCM may not manage cooling fans or fuel trim correctly. Avoid towing or heavy-load driving until diagnosed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P00B6 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Cooling System
Difficulty
Type
Generic (SAE)
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