Evaporative Emissions System: Testing and Inspection

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
The Evaporative Emission ([1][2]EVAP) system is tested by applying vacuum to the EVAP system and monitoring for a vacuum decay. The PCM monitors the vacuum level through the fuel tank vapor pressure sensor signal. At an appropriate time, the EVAP canister purge valve and the EVAP vent solenoid are turned on, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge valve is turned off, sealing the system. A leak is detected by monitoring for a decrease in vacuum level over a given time period, when all other variables remain constant. A leak, blockage or poor component in the system will cause a DTC to set.

DIAGNOSIS
^ The EVAP canister purge valve operation is covered and diagnosed in DTCs P0440, P0446, and P1441.
^ The EVAP vent valve operation is covered and diagnosed in DTCs P0440, P0442, and P0446.
^ The fuel tank vapor pressure sensor operation is covered and diagnosed in DTCs P0440, P0442, P0446, P0452, P0453, P1441 and in the Evaporative Emission System Check.
^ A open or a shorted circuit in the EVAP canister purge valve and EVAP vent valve can also be diagnosed in PCM Outputs Diagnosis.

VISUAL CHECK OF THE EVAP CANISTER
If the canister is cracked or damaged, replace the canister.

DIAGNOSTIC AIDS
Inspect for the following conditions:
^ Poor connection at PCM. Inspect harness connectors for the following conditions:
- Backed out terminals
- incorrect mating
- Broken locks
- incorrectly formed
- Damaged terminals
- Poor terminal to wire connection
^ A damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Vacuum Pressure on a scan tool while moving the electrical connectors and the wiring harnesses related to the sensor. A change in the display will indicate the location of the malfunction
^ An incorrect purge or vacuum source line routing Verify that the source vacuum and purge lines to the EVAP canister purge valve are not switched