How to troubleshoot a P0442 code on a Ford
Understanding and fixing a P0442 Code on a Ford Vehicle
The P0442 code is a common diagnostic trouble code on Ford vehicles. It indicates a small leak has been detected in the evaporative emission (EVAP) system. This code appears so often on Ford vehicles because of a fault in the capless flap gas tank filler device. Ford has had some problems with the capless flap gas-filling device mounted in the filler neck. If installing a capless flap doesn’t fix the P0442 problem, continue to test the vent and purge solenoid valves and the fuel tank pressure sensor (FTP).
Ford has had many problems with their capless flap gas cap
How to test the fuel tank pressure sensor
The fuel tank pressure sensor should show 2.6 volts while the EVAP system is open and then drop to 1.0 volts or less when the purge valve is open and the engine is running. In other words, the engine is pulling a vacuum on the entire EVAP system. When the purge valve closes, 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 a reference signal to return 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 the engine from dying.
However, if the power steering pressure sensor develops an internal short to the reference voltage, the return voltage will be higher. That’ll trick 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 Muscoplat
Posted on by Rick Muscoplat