The basic Evaporative Emission (EVAP) Control system used on all vehicles is the charcoal canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon (charcoal) storage device (canister) to hold the vapors when the vehicle is not operating. When the engine is running, the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.
Gasoline vapors from the fuel tank flow into the tube labeled tank. Refer to the Evaporative Emission Canister graphic. These vapors are absorbed into the carbon. The canister is purged by PCM control when the engine coolant temperature is over 41°C (106°F), IAT reading is over 0°C (32°F), and the engine has been running a specified amount of time. Air is drawn into the canister through the air inlet grid. The air mixes with the vapor and the mixture is drawn into the intake manifold.
Canister purge is controlled by a solenoid valve that allows manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground to energize the solenoid valve (purge 'ON'). The EVAP purge solenoid 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:
| • | Engine is fully warmed up. |
| • | After the engine has been running a specified time. |
| • | IAT reading above 0°C (32°F). |
The EVAP purge vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge solenoid. The EVAP Purge Vacuum Switch will open when vacuum increases to greater than 5 inches of water in the purge line. The EVAP Purge Vacuum Switch is used by the PCM to monitor EVAP canister purge solenoid operation and purge system integrity. The EVAP Purge Vacuum Switch should be closed to ground with no vacuum present (0% EVAP Purge PWM). With EVAP Purge PWM at 25% or greater, the EVAP Purge Vacuum Switch should open.
An incorrect EVAP Purge system flow should set a DTC P0441. A continuous purge condition with no purge commanded by the PCM should set a DTC P1441. A fault in the EVAP Purge Vacuum Switch circuit should set a DTC P1442.
Poor idle, stalling and poor driveability can be caused by:
| • | Malfunctioning purge solenoid. |
| • | Damaged canister. |
| • | Hoses split, cracked and/or not connected properly. |
Canister Purge Solenoid and EVAP Vacuum Switch
An incorrect EVAP Purge system flow should set a DTC P0441. A Continuous Purge Condition with no purge commanded by the PCM should set a DTC P1441. A fault with the EVAP Vacuum Switch circuit should Set a DTC P1441.
Visual Check of the EVAP Canister
Check the EVAP canister for the following conditions:
| • | Cracked or damaged, replace canister. |
| • | Fuel leaking from the canister; replace canister and check hoses and hose routing. |
