P00B6
Radiator Coolant Temperature/Engine Coolant Temperature CorrelationP00B6 is a generic OBD-II powertrain diagnostic trouble code: Radiator Coolant Temperature/Engine Coolant Temperature Correlation. It is logged by the engine control unit when the coolant monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P00B6 means
DTC P00B6 is set when the powertrain control module (PCM) detects an excessive difference between the signal from the radiator coolant temperature (RCT) sensor and the engine coolant temperature (ECT) sensor. Modern engines use both sensors to accurately monitor the thermal state of the cooling circuit: the ECT typically measures coolant at the engine outlet (hot side) while the RCT measures coolant returning from the radiator (cold side). The PCM continuously compares these two readings; under normal operation the spread is predictable and follows expected warm-up curves. A P00B6 code is logged when the absolute difference between the two sensor readings exceeds the manufacturer-calibrated threshold — commonly around 20 °C (68 °F) during a cold-start warm-up sequence — or when one sensor fails to track the expected rise in relation to the other. This can indicate that the cooling circuit is not circulating properly (failed thermostat, coolant loss), that one of the sensors is faulty or out of calibration, or that there is a wiring or PCM fault affecting signal accuracy. Because the PCM uses this correlation to optimize fuelling, cooling fan commands, and emissions readiness, a persistent correlation fault can degrade performance and increase emissions.
Common causes
Most-frequently reported root causes when P00B6 is logged.
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1
Stuck-open or stuck-closed thermostat preventing normal coolant temperature differential
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2
Low coolant level causing air pockets and inconsistent sensor readings
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3
Coolant leak within the cooling circuit disrupting normal flow
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4
Faulty or out-of-calibration radiator coolant temperature sensor
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5
Faulty or out-of-calibration engine coolant temperature sensor
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6
Wiring or connector fault on either sensor circuit introducing resistance or shorts
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7
Faulty PCM or software calibration issue causing incorrect comparison threshold
Symptoms drivers notice
How to diagnose P00B6
A typical diagnostic flow when this code is present.
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1
Retrieve all stored DTCs and freeze-frame data; note exact coolant temperatures at the time the code set, which helps determine which sensor appears out of range
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2
Verify coolant level is correct and inspect the cooling system for visible leaks at hoses, the radiator, water pump, and thermostat housing
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3
With the engine cold (off for at least 8 hours), monitor live sensor data on a scan tool — both RCT and ECT should read within a few degrees of each other and close to ambient temperature; a large discrepancy at cold soak points to a faulty sensor
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4
Perform a warm-up test: start the engine and watch both sensors rise together on the scan tool; ECT should climb ahead of RCT; if either sensor is stuck or lags abnormally, test it with a multimeter against the temperature-resistance chart
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5
Inspect the thermostat by monitoring warm-up rate — engine temperature should climb steadily and then stabilize; a stuck-open thermostat causes very slow warm-up; a stuck-closed thermostat causes rapid overheating
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6
Test wiring continuity and check for shorts or high resistance on both sensor circuits between sensor and PCM
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7
If both sensors and coolant system check out, consult manufacturer TSBs for PCM calibration updates before condemning the module
Related powertrain codes
- P008F — Engine Coolant Temperature/Fuel Temperature Correlation
- P00B1 — Radiator Coolant Temperature Sensor Circuit
- P00B2 — Radiator Coolant Temperature Sensor Circuit Range/Performance
- P00B3 — Radiator Coolant Temperature Sensor Circuit Low
- P00B4 — Radiator Coolant Temperature Sensor Circuit High
- P00B5 — Radiator Coolant Temperature Sensor Circuit Intermittent/Erratic
Frequently asked questions
What is the most common cause of P00B6?
A faulty thermostat is one of the most frequent causes, as a stuck-open thermostat allows coolant to circulate through the radiator before reaching operating temperature, keeping radiator-side temperatures disproportionately low relative to engine-side readings. Low coolant level is another very common trigger.
Can P00B6 cause overheating?
Yes, indirectly. If the code is triggered by a stuck-closed thermostat or a cooling system blockage, actual overheating is a real risk. Even if the sensors themselves are at fault and coolant circulation is normal, relying on miscorrelated sensor data can lead the PCM to make incorrect cooling fan decisions.
Do I need to replace both sensors when P00B6 sets?
Not necessarily. Diagnose which sensor is reading incorrectly by comparing both against a known-good temperature reference (such as an infrared thermometer on the coolant hose). Only replace the sensor that is confirmed out of specification.
Will P00B6 affect my emissions test?
It can. P00B6 may prevent certain readiness monitors from completing their drive cycles, which will result in a "not ready" status and a failed OBD-II emissions inspection in many jurisdictions. The underlying fault must be resolved and a full drive cycle completed to set all monitors ready.
Disabling P00B6 in software
RaceTune can permanently disable P00B6 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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