Fuel Tank Assembly With EVAP Canister

Fuel Tank Assembly With EVAP Canister:

The evaporative leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring the vacuum decay.

The PCM monitors the vacuum level via the fuel tank pressure sensor input. At an appropriate time, the EVAP purge solenoid and the EVAP vent solenoid are turned on, allowing engine vacuum to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP purge solenoid is turned off, sealing the system. A leak is detected by monitoring for a decrease in the vacuum level during a specific time period, with all other variables remaining constant. A small leak in the system causes DTC P0442 to be set.

If the desired vacuum level cannot be achieved in the test described above, a large leak or a faulty EVAP purge solenoid is indicated. This condition can be caused by the following conditions:
^ A disconnected or faulty fuel tank pressure sensor
^ A missing or faulty fuel cap
^ A disconnected, damaged, pinched, or blocked EVAP purge line
^ A disconnected or damaged EVAP vent hose
^ A disconnected, damaged, pinched, or blocked fuel tank vapor line
^ A disconnected or faulty EVAP canister solenoid
^ A disconnected or faulty EVAP vent solenoid
^ An open ignition feed circuit to the EVAP vent or to the purge solenoid
^ A damaged EVAP canister

Any of the above conditions will set DTC P0440.

A restricted or blocked EVAP canister vent path is detected by drawing vacuum into the EVAP system. The PCM turns off the EVAP vent solenoid and the EVAP purge solenoid, with the EVAP vent solenoid Open, and with the EVAP purge PWM at 0 percent.

The PCM monitors the fuel tank pressure sensor input. With the EVAP vent solenoid open, any vacuum in the system should decrease quickly unless the vent is blocked. The following conditions cause a blockage:
^ A faulty or stuck closed EVAP vent solenoid
^ A plugged, kinked, or pinched vent hose
^ A shorted EVAP vent solenoid driver circuit
^ A plugged evaporative canister

If any of the above conditions are present, DTC P0446 sets.

The PCM checks for conditions that cause the EVAP system to purge continuously by commanding the EVAP vent solenoid on and by commanding the EVAP purge solenoid off, with the EVAP vent solenoid CLOSED, and the EVAP purge PWM at 0 percent. If fuel tank pressure level increases during the test, a continuous purge flow condition is indicated. This condition can be caused by the following conditions:
^ A leaking EVAP purge solenoid
^ EVAP purge lines and engine vacuum source lines that are switched at the EVAP purge solenoid
^ An EVAP purge solenoid driver circuit that is grounded

If any of the above conditions are present, DTC P1441 sets.

Refer to the appropriate DTCs for further diagnostic procedures regarding the EVAP system.