System Description
The Evaporative (EVAP) emission system includes the following components:
- Fuel tank
- EVAP emission vent solenoid
- Fuel tank pressure sensor
- Fuel pipes and hoses
- Fuel vapor lines
- Fuel cap
- EVAP emission canister
- Purge lines
- EVAP emission canister purge valve
- EVAP emission service port
The EVAP emission system is checked by applying vacuum to the EVAP emission system and monitoring for a vacuum decay. The Engine Control Module (ECM) monitors the vacuum level through the fuel tank pressure sensor signal.
At the appropriate time, the EVAP emission canister purge valve and the EVAP emission vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire EVAP emission system. After the desired vacuum level has been achieved, the EVAP emission canister purge valve is turned OFF, sealing the system. The EVAP emission canister purge valve allows manifold vacuum to purge the canister. The ECM supplies a ground to energize the solenoid valve (purge ON). The EVAP emission canister 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 (TP), Engine Coolant Temperature (ECT) and ambient temperature. The duty cycle is calculated by the ECM and the output is commanded when the appropriate conditions have been met.
The system checks for conditions that cause the EVAP emission system to purge continuously by commanding the EVAP emission vent solenoid ON and the EVAP emission canister purge valve OFF (EVAP emission vent solenoid CLOSED, EVAP emission purge PWM 0%).
If the fuel tank vacuum level increases during the test, a continuous purge flow condition is indicated. This can be caused by the following conditions:
- EVAP emission canister purge valve leaking
- EVAP emission purge and engine vacuum lines switched at the EVAP emission canister purge valve.
- EVAP emission canister purge valve driver circuit grounded.
If any of these conditions are present, DTC P0496 will set.