Fix a P0442 leak and P0442 code comes back
If your Ford shows a P0442 Evaporative Emission Control System Leak Detected (small leak), you should know that Ford has had some problems with the capless flap in the gas tank filler neck. If installing a new one doesn’t fix the P0442 problem, continue to test the vent and purge solenoid valves, as well as the fuel tank pressure sensor (FTP).
The FTP should show 2.6-volts while the EVAP system is open and then drop to 1.0-volt or less when the purge valve is open and engine is running. In other words, the engine is pulling a vacuum on the entire EVAP system. When you close the purge valve, the FTP reading should remain the same. If it rises, that would seem to indicate a leak in the system—but not always.
Ford sends a reference voltage to the FTP sensor and expects to see a reference signal return back to the PCM on the yellow/violet wire. I’m guessing that Ford also wanted to save some wire by using the same yellow/violet wire as the signal return for the power steering pressure sensor. The PCM monitors the power steering pressure sensor to increase engine RPMs when you’re in a parking lot and doing parking maneuvers. The increased RPMs prevent engine dying. However, if the power steering pressure sensor develops and internal short to reference, the return voltage will be higher, tricking the PCM into thinking you’ve got an EVAP system leak. The lesson here is to disconnect the power steering pressure sensor BEFORE you condemn the FTP sensor. With the power steering pressure sensor out of the circuit, repeat the purge and hold test. If the FTP voltage stays low, replace the power steering pressure switch.
©, 2015 Rick MuscoplatPosted on by Rick Muscoplat