Monitoring function of the canister purge solenoid (CPS)

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The diagnosis is used for the functional test of the CP solenoid (CPS). The test consists of three checks.

The first check of the CPS is based on the active charcoal filter (ACF) amount. The "Canister Load diagnosis" is calculated permanently until the complete check CPS is finished.

If amount is above threshold ok is detected.

If amount is below threshold, the next step will be performed.

During the next check, the CPS is evaluated based on manifold pressure change or engine speed change (respectively in case of high manifold pressure -) at idle speed. To this effect, the CPS is opened for a short time and the engine speed monitored for a certain period. Additionally the deviation of lambda-controller (rich mixture) is monitored.

After this check has been enabled for the first time, it is requested during each idle speed phase as long as the conditions are met. This is repeated as long as a result has been reached. This check is not bound to one idle speed phase, but can be distributed to several idle speed phases.

If the CPS is detected to be not ok three times, the error is set.

If no error is detected then a third check will be performed (only in case of high manifold pressure):

The principle of the third CPS check is based on the measured mass air flow before and during a CPS opening phase.

If there is no change in mass air flow, then the error is set.