Method and system for diagnosing evaporative emissions control system
Methods and systems are presented for diagnosing operation of an evaporative emissions system that included two carbon filled fuel vapor storage canisters that are arranged in parallel. In one example, operation of a first canister vent valve, a second canister vent valve, and a canister purge valve are adjusted to diagnose breaches and obstructions within the evaporative emissions system.
1 . A method for operating an evaporative emissions system of a vehicle, comprising:
commanding open a first canister vent valve, a second canister vent valve, and a canister purge valve during an initial phase of an evaporative emissions system diagnostic, where the first canister vent valve is arranged in parallel with the second canister vent valve;
commanding closed the second canister vent valve, commanding open the first canister vent valve and the canister purge valve during a first phase of the evaporative emissions system diagnostic;
commanding closed the first canister vent valve, commanding open the second canister vent valve and the canister purge valve during a second phase of the evaporative emissions system diagnostic; and
commanding closed the first canister vent valve and the second canister vent valve, and commanding open the canister purge valve during a third phase of the evaporative emissions system diagnostic.
2 . The method of claim 1 , further comprising generating an indication of evaporative emissions degradation in response to output of a pressure sensor not being within a threshold range during the initial phase of the evaporative emissions system diagnostic.
3 . The method of claim 2 , further comprising generating a second indication of evaporative emissions degradation in response to output of the pressure sensor not being within a second threshold range during the first phase of the evaporative emissions system diagnostic.
4 . The method of claim 3 , further comprising generating a third indication of evaporative emissions degradation in response to output of the pressure sensor not being within a third threshold range during the second phase of the evaporative emissions system diagnostic.
5 . The method of claim 4 , further comprising generating a fourth indication of evaporative emissions degradation in response to output of the pressure sensor not being within a fourth threshold range during the third phase of the evaporative emissions system diagnostic.