This function is a test that checks and reads out the engine's fuel pressure. The fuel pressure is periodically read out from the after-treatment fuel pressure sensor. During this sequence, a snapshot of the fuel supply pressure is made. The pressure is read when the after-treatment hydrocarbon dosing valve is closed and the fuel cut off valve is open.
If the reading of "Aftertreatment fuel pressure" is lower than "Fuel supply pressure, low limit", a fault code with low fuel pressure will be set.