Evaporative Emissions System: Testing and Inspection

Refer to Emission Hose Routing Diagram, EVAP System Overview.

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

SYSTEM DESCRIPTION
The EVAP canister purge valve allows manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground to energize the purge valve. The [1][2]EVAP purge valve control is Pulse Width Modulated (PWM) or turned ON and OFF several times a second. The duty cycle, pulse width, is determined by engine operating conditions including load, throttle position, coolant temperature, and ambient temperature. The duty cycle is calculated by the PCM and the output is commanded when the appropriate conditions have been met.

The EVAP vent valve is used to seal the EVAP system during diagnostic tests. The fuel tank pressure sensor is used to monitor vacuum in the system during the diagnostic tests.

A stuck closed EVAP canister purge valve, stuck open EVAP vent valve, disconnected or damaged [1][2]EVAP purge line or vent hose, leaking fuel cap, or till neck should set a DTC P0440. A small leak in the EVAP system should set a DTC P0442. An EVAP vent valve stuck closed, a restricted vent hose, or a blocked EVAP canister should set a DTC P0446. A continuous purge condition with no purge commanded by the PCM, EVAP purge valve stuck open or leaking, should set a DTC P1441. Refer to the DTC tables for further diagnostic procedures regarding the EVAP system.

The EVAP system includes the following components:
^ The EVAP canister
^ The EVAP canister purge valve
^ The EVAP vent valve The [1][2]EVAP vapor pipes
^ The [1][2]EVAP purge pipes
^ The [1][2]EVAP fresh air vent hose
^ The fuel tank
^ The fuel pipes and hoses
^ The fuel fill cap
^ The fuel fill pipe

DIAGNOSTIC AIDS
Inspect for the following conditions:
^ Cracked or punctured EVAP canister
^ Damaged or disconnected source vacuum line, [1][2]EVAP purge line, vent hose, or fuel tank vapor line
^ Faulty connection at the PCM
^ Inspect harness connectors for the following conditions:
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Faulty terminal to wire connection
^ Damaged harness Inspect the wiring harness to the EVAP vent valve, the [1][2]EVAP purge valve, and the fuel tank pressure sensor for an intermittent open or short circuit.
^ Kinked, pinched, or plugged vacuum source, [1][2]EVAP purge, or fuel tank vapor line-Verify that the lines are not restricted.
^ Carbon released into the system