P008F Engine Coolant Temperature/Fuel Temperature Correlation
OBD-II Trouble Code Technical Description
Engine Coolant Temperature/Fuel Temperature Correlation
What does that mean?
This generic powertrain diagnostic trouble code (DTC) typically applies to many OBD-II vehicles. That may include but is not limited to vehicles from Mercedes-Benz, Chevrolet, Sprinter, GMC, Ford, etc.
When your OBD-II equipped vehicle exhibits a service engine soon lamp and a code P008F is stored, it means that the powertrain control module (PCM) has detected a discrepancy in the correlating signals between perceived engine coolant temperature (ECT) and fuel temperature.
Engine coolant temperature and fuel temperature are typically monitored in comparison only when the engine is at ambient temperature.
ECT sensors are composed of a thermal resistor that is dipped in a hard resin and sealed in a metal or plastic housing. Brass is the most common metal used as ECT sensor housing material. The ECT housing is designed so that it may be threaded into a coolant passage in the engine intake manifold, cylinder head, or block. As warm coolant passes through the passages and across the ECT sensor, the level of thermal resistance in the ECT decreases. When engine coolants decreases in temperature, resistance increases and ECT sensor circuit voltage is reduced as a result. These fluctuations in resistance (which result in voltage variations) are interpreted by the PCM as changes in engine coolant temperature. ECT sensor input data is critical in calculating fuel delivery and ignition timing strategy.
The fuel temperature sensor also uses a thermal resistor but it is of the low voltage variety. It is most often integrated into the fuel level sending unit and provides the PCM with a voltage signal that reflects fuel temperature whenever the ignition is in the ON position. Fuel temperature can be especially crucial to drivability in vehicle applications which utilize a diesel engine. Fuel temperature is also more of a concern in extremely cold climates.
A code P008F will be stored and a malfunction indicator lamp (MIL) may be illuminated if the PCM detects a discrepancy (between the ECT sensor and the fuel temperature sensor) which varies by more than the maximum allowable parameters over a set period of time and under a certain set of circumstances.
What is the severity of this DTC?
Since ECT and fuel temperature are so important to fuel delivery and ignition timing strategy, a stored code P008F should be addressed with some degree of urgency.
What are some of the symptoms of the code?
Symptoms of a P008F engine code may include:
Reduced engine performance Diminished fuel efficiency Excessively rich exhaustWhat are some of the common causes of the code?
Causes for this engine code may include:
Faulty ECT sensor Bad fuel temperature sensor Open or shorted wiring or connector PCM or PCM programming errorWhat are some P008F troubleshooting steps?
Any stored ECT sensor related codes, would prompt me to make sure that the engine is not overheating. It should be full of coolant and operating within the acceptable temperature guidelines. If the engine is not overheating, a visual inspection of ECT sensor and fuel temperature sensor system wiring and connectors should be your next step.
A diagnostic scanner, a digital volt/ohmmeter (DVOM), an infrared thermometer with a laser pointer, and a source of reliable vehicle information will be required before attempting to diagnose a code P008F.
Now, connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. Write this information down as it may be helpful as you continue to go deeper into the diagnostic process. Next, you will want to clear the codes and test-drive the vehicle to see if the code is reset.
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