Code P008F: Coolant Temperature / Fuel Temperature Correlation
The generic diagnostic trouble code P008F is a powertrain Diagnostic Trouble Code (DTC) applicable to many OBD-II equipped vehicles, including Mercedes-Benz, Chevrolet, Ford, GMC, and Sprinter. It is stored when the Powertrain Control Module (PCM) detects an anomaly in the correlation between the Engine Coolant Temperature (ECT) sensor signal and the Fuel Temperature sensor signal.
Symptoms of Code P008F
When this code is active, you may observe several symptoms affecting the vehicle’s performance:
- Decreased engine performance and power.
- Noticeable reduction in fuel efficiency (increased fuel consumption).
- Overly rich air-fuel mixture, which can lead to excessive exhaust smoke.
Potential Causes of the Fault
Several failures can cause the P008F code:
- A faulty Engine Coolant Temperature (ECT) sensor.
- A defective Fuel Temperature sensor.
- A wiring issue (short circuit, open circuit, corroded or loose connector).
- A programming error or internal PCM failure (less common).
How to Diagnose Code P008F?
Diagnosis requires an OBD2 scanner, a digital multimeter (DVOM), and possibly an infrared thermometer. Follow this procedure:
- Preliminary Check: Check the coolant level and condition. Ensure the engine is not overheating.
- Visual Inspection: Inspect the wiring and connectors of both sensors (ECT and Fuel Temperature) for any obvious signs of damage, corrosion, or poor connection.
- Code Reading: Using the scanner, retrieve all fault codes and freeze frame data. Note them down and then clear the codes. Perform a road test to see if the P008F code reappears.
- Sensor Testing: Using a multimeter and the manufacturer’s specifications, test the resistance of the ECT and Fuel Temperature sensors (with the engine cold and hot). Compare the measured values with the reference values.
- Circuit Testing: Check for the presence of reference voltage (5V) and ground at the sensor connectors (ignition on, engine off). Test for continuity and the absence of short circuits in the wires connecting the sensors to the PCM.
- Advanced Diagnosis: Using the infrared thermometer, measure the actual temperature of the coolant and fuel. Compare these values with the signal voltage data sent by the sensors to the PCM via your scanner. A discrepancy indicates a faulty sensor.
Only suspect a PCM failure after all other possible causes have been eliminated.
Severity and Recommended Actions
The severity of code P008F is moderate to high. Although the vehicle may remain drivable, a failure of the temperature sensors can lead to poor engine management, increased fuel consumption, and potentially damage the catalytic converter. It is recommended to perform the diagnosis as soon as possible.
⚠️ Need help diagnosing your vehicle? Consult your manufacturer’s technical service bulletins or seek assistance from a professional mechanic equipped with the appropriate diagnostic tools for accurate and effective troubleshooting.