Emission Control Systems: Description and Operation

If the vehicle was refueled and the filler cap was not properly installed, the Check Filler Cap message will be displayed in the instrument cluster for 20 seconds.
If the filler cap is installed and there is no leakage present the next time the leakage test is performed, the Malfunction Indicator Light will not be illuminated (additional detailed information on page 82 of Workshop Hints).





Evaporative Emission Purging is regulated by the ECM controlling the Evaporative Emission Valve.
The Evaporative Emission Valve is a solenoid that regulates purge flow from the Active Carbon Canister into the intake manifold. The ECM Relay provides operating voltage, and the ECM controls the valve by regulating the ground circuit. The valve is powered open and closed by an internal spring.
The purging process takes place when:
^ Oxygen Sensor Control is active
^ Engine Coolant Temperature is >67°C
^ Engine Load is present
The Evaporative Emission Valve is opened in stages to moderate the purging.
^ Stage 1 opens the valve for 10 ms (milk-seconds) and then closes for 150 ms.
^ The stages continue with increasing opening times (up to 16 stages) until the valve is completely open.
^ The valve now starts to close in 16 stages in reverse order
^ This staged process takes 6 minutes to complete. The function is inactive for 1 minute then starts the process all over again.
^ During the purging process the valve is completely opened during full throttle operation and is completely closed during deceleration fuel cutoff.

Evaporative Purge System Flow Check is performed by the ECM when the oxygen sensor control and purging is active. When the Evaporative Emission Valve is open the ECM detects a rich/lean shift as monitored by the oxygen sensors indicating the valve is functioning properly.
If the ECM does not detect a rich/lean shift, a second step is performed when the vehicle is stationary and the engine is at idle speed. The ECM opens and close the valve (abruptly) several times and monitors the engine rem for changes. If there are no changes, a fault code will be set.

Misfire Detection



Testing the Oxygen Sensor should be performed using the DlSplus Oscilloscope from the "Preset Measurement" List. The scope pattern should appear as below for a normal operating sensor.
If the signal remains high (rich condition) the following should be checked:
^ Fuel Injectors
^ Fuel Pressure
^ Ignition System
^ Input Sensors that influence air/fuel mixture
^ Engine Mechanical
If the signal remains low (lean condition) the following should be checked:
^ Air/Vacuum leak
^ Fuel Pressure
^ Input Sensor that influence air/fuel mixture
^ Engine Mechanical

NOTE: A MIXTURE RELATED FAULT CODE SHOULD BE INVESTIGATED REST AND DOES NOT ALWAYS INDICATE A DEFECTIVE OXYGEN SENSOR,

Check Filler Cap

After refueling and switching the ignition ON, the ECM detects a fuel level increase. When the ignition is switched OFF, the ECM activates the DM TL for a brief test to check the filler cap. If the filler cap was not properly installed; when the vehicle is started and driven at a speed >10 Km/h, the Check Filler Cap light will illuminate for 25 seconds (and then go out)
The second time the ignition is cycled OFF, the DM TL is activated to test the filler cap. If loose; when the vehicle is started and driven at a speed >10 Km/h, the Check Filler Cap light will be illuminated for 25 seconds (and then go out).
If the filler cap is properly secured, the Malfunction Indicator Light will not be illuminated and a fault code will not be stored in the ECM.
The third time the ignition is cycled OFF, the DM TL is activated to test the filler cap. If loose; a Large Leak fault code is stored in the ECM. The Malfunction Indicator Light will be illuminated the next time the engine is started.