EMISSION CONTROL - K SERIES KV6 Leak Diagnostic Operation To check the fuel tank and EVAP system for leaks, the ECM operates the air pump in the DMTL and monitors the current draw. Initially, the ECM establishes a reference current by pumping air through the reference orifice and back to atmosphere. Having established a reference current, the ECM then closes the change-over valve, which seals the EVAP system (the purge valve already being closed), and diverts the output from the air pump around the reference orifice and into the EVAP system. When the change-over valve is first closed, the load on the pump drops to zero, then, provided there are no leaks, the pump begins to pressurise the EVAP system and the load and current draw of the pump begin to increase. By monitoring the rate and level of current increase, the ECM can determine if there is a leak in the system. During the leak check, the ECM energises a heating element in the air pump to prevent condensation forming and producing an incorrect current reading. Leaks are classified as minor (equivalent to hole diameter of 0.5 to 1.0 mm (0.02 to 0.04 in) or major (equivalent to hole diameter of 1.0 mm (0.04 in) or greater). The ECM conducts a check for major leaks each time the ignition is switched off, provided the following baseline conditions are met: l The ECM is in power down mode more than 3 seconds after the ignition is switched off. l The vehicle speed is zero. l The engine speed is zero. l The pressure altitude (derived from engine load calculations) is below 1830 m (6000 ft). l The engine coolant temperature is more than 2.25 °C (36 °F). l The ambient temperature is between 0 and 40 °C (32 and 104 °F). l The EVAP canister load factor is 3 or less (the load factor is a measure, between –1 and +30, of the amount of fuel vapour stored in the EVAP canister, where –1 is 0% fuel vapour, 0 is stoichiometric fuel vapour level and +30 is 100% saturated with fuel vapour). l The fuel tank level is valid and between 15 and 85 % of the nominal capacity. l The engine running time during the previous ignition on cycle was more than 20 minutes. l Battery voltage is between 10.94 and 14.52 volts. l The last engine off time was more than 150 minutes. l No errors with the following functions or components: l Road speed. l EVAP system load monitoring. l Engine coolant temperature. l Ambient air temperature. l Fuel level. l Purge valve. l DMTL.
DESCRIPTION AND OPERATION
17-3-9
