System and method for diagnosing faults in vacuum pumps of fuel systems and for diagnosing leaks in fuel systems

1. A control system, comprising:

a switching valve control module that actuates a switching valve in a fuel system of a vehicle between a first position and a second position, the first position venting a suction side of a vacuum pump in the fuel system to an atmosphere, the second position sealing the suction side of the vacuum pump from the atmosphere;

a pressure determination module that:

determines a first pressure on the suction side of the vacuum pump when the switching valve is in the first position; and

determines a second pressure on the suction side of the vacuum pump when the switching valve is in the second position; and

a fuel system diagnostic module that selectively determines that the vacuum pump is stuck on based on the first pressure and the second pressure.

2. The control system of claim 1 , wherein the fuel system diagnostic module determines that the vacuum pump is stuck on when a first difference between the first pressure and the second pressure is greater than a first threshold.

3. The control system of claim 2 , wherein the fuel system diagnostic module determines the first threshold based on a flow capacity of the vacuum pump.

4. The control system of claim 1 , wherein the pressure determination module determines the first pressure when the vehicle is off for a predetermined period.

5. The control system of claim 1 , further comprising a pump control module that controls the vacuum pump, wherein the pressure determination module determines the first pressure and the second pressure when the vacuum pump is commanded off.

6. The control system of claim 1 , further comprising a vent valve control module that controls a vent valve in the fuel system, wherein the pressure determination module determines the first pressure and the second pressure when the vent valve is commanded closed.

7. The control system of claim 1 , further comprising a purge valve control module that controls a purge valve in the fuel system, wherein the pressure determination module determines the first pressure and the second pressure when the purge valve is commanded closed.

8. The control system of claim 7 , wherein:

the pressure determination module determines a third pressure when the switching valve is in the first position and the vacuum pump is commanded on;

the pressure determination module determines a fourth pressure when the switching valve is in the second position and the vacuum pump is commanded on; and

the fuel system diagnostic module selectively diagnoses a leak in the fuel system when a second difference between the third pressure and the fourth pressure is less than a second threshold.

9. The control system of claim 8 , wherein the fuel system diagnostic module determines the second threshold based on at least one of the first pressure, the second pressure, and the third pressure.

10. The control system of claim 8 , wherein the fuel system diagnostic module refrains from diagnosing a leak in the fuel system when the fuel system diagnostic module diagnoses a fault in the vacuum pump.

11. A method, comprising:

actuating a switching valve in a fuel system of a vehicle between a first position and a second position, the first position venting a suction side of a vacuum pump in the fuel system to an atmosphere, the second position sealing the suction side of the vacuum pump from the atmosphere;

determining a first pressure on the suction side of the vacuum pump when the switching valve is in the first position;

determining a second pressure on the suction side of the vacuum pump when the switching valve is in the second position; and

selectively determining that the vacuum pump is stuck on based on the first pressure and the second pressure.

12. A method, comprising:

actuating a switching valve in a fuel system of a vehicle between a first position and a second position, the first position venting a suction side of a vacuum pump in the fuel system to an atmosphere, the second position sealing the suction side of the vacuum pump from the atmosphere;

determining a first pressure on the suction side of the vacuum pump when the switching valve is in the first position;

determining a second pressure on the suction side of the vacuum pump when the switching valve is in the second position;

selectively diagnosing a fault in the vacuum pump based on the first pressure and the second pressure; and

determining that the vacuum pump is stuck on when a first difference between the first pressure and the second pressure is greater than a first threshold.

13. The method of claim 12 , further comprising determining the first threshold based on a flow capacity of the vacuum pump.

14. The method of claim 11 , further comprising determining the first pressure when the vehicle is off for a predetermined period.

15. The method of claim 11 , further comprising determining the first pressure and the second pressure when the vacuum pump is commanded off.

16. The method of claim 11 , further comprising determining the first pressure and the second pressure when a vent valve is commanded closed.

17. The method of claim 11 , further comprising determining the first pressure and the second pressure when a purge valve is commanded closed.

18. The method of claim 17 , further comprising:

determining a third pressure when the switching valve is in the first position and the vacuum pump is commanded on;

determining a fourth pressure when the switching valve is in the second position and the vacuum pump is commanded on; and

selectively diagnosing a leak in the fuel system when a second difference between the third pressure and the fourth pressure is less than a second threshold.

19. The method of claim 18 , further comprising determining the second threshold based on at least one of the first pressure, the second pressure, and the third pressure.

20. The method of claim 18 , further comprising refraining from diagnosing a leak in the fuel system when a fault in the vacuum pump is diagnosed.