DF239 OBD2 reports a sensor fault, replacement of the sensor is unlikely to resolve the underlying problem. The fault is most likely to be caused by the systems that the sensor is monitoring, but might even be caused by the wiring to the sensor itself.
The sensors receive a 5 volt reference signal from the PCM. As pressure readings change, the sensor varies the voltage and the computer reads that to determine input. In the case of a broken wire, the sensor never sees the voltage and the computer assumes a major fault. So if you get this DF239 code, first check to make sure you're getting a good 5 volt reference signal at the sensor.
The problem is caused by the variable cylinder management system switching on and off during light throttle conditions, at cruising speeds, or when driving on flat roads. The constant switching causes excessive oil consumption and the trouble codes appear when oil pressure drops to the point where it can no longer operate the VCM system.
In-line Ford engines, along with those of most other manufacturers, begin the numbering of cylinders at the front and proceed in numerical order toward the back. In the V-engine design, Ford follows a similar design with the number one cylinder at the front left of the engine. In the V-6 configuration, cylinder 4 is at the front right of the engine and in a V-8, cylinder number 5 is in that location. Other manufacturers sometimes use an alternating pattern in the V-engines.
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