System and method to diagnose fuel system pressure sensor

1. A system comprising:

a pressure sensor that generates a first pressure signal indicating a first pressure within a fuel system of an engine when the engine is started and when a purge valve of the fuel system is closed; and

a controller configured to:

detect when the engine is started,

determine an amount of variation in the first pressure signal over a first period,

determine a state of the pressure sensor based on the amount of variation in the first pressure signal over the first period, and

determine that the pressure sensor operates normally if the amount of variation in the first pressure signal is less than a first threshold and that the pressure sensor is faulty if the amount of variation in the first pressure signal is greater than or equal to the first threshold,

wherein the first threshold is determined based on a leakage rating of the purge valve, and

wherein the leakage rating of the purge valve is non-zero.

2. The system of claim 1 wherein the controller is configured to determine the amount of variation in the first pressure signal based on a difference between a current pressure reading and a previous pressure reading, an absolute value of the difference between the current pressure reading and the previous pressure reading, and a running total of the absolute value of the difference between the current pressure reading and the previous pressure reading over the first period.

3. The system of claim 1 wherein the pressure sensor subsequently generates a second pressure signal indicating a second pressure within the fuel system when the purge valve of the fuel system is cycled at a duty cycle, wherein the controller is configured to determine an amount of variation in the second pressure signal over a second period, and wherein the controller is further configured to:

diagnose a fault associated with flow through the purge valve if the amount of variation in the first pressure signal is less than the first threshold and the amount of variation in the second pressure signal is less than a second threshold.

4. The system of claim 3 wherein the controller is configured to determine the amount of variation in the second pressure signal based on a difference between a current pressure reading and a previous pressure reading, an absolute value of the difference between the current pressure reading and the previous pressure reading, and a running total of the absolute value of the difference between the current pressure reading and the previous pressure reading over the second period.

5. The system of claim 3 wherein the controller is configured to determine the second threshold based on a predetermined relationship between a flow restriction in the purge valve and the amount of variation in the second pressure signal.

6. The system of claim 3 wherein the controller is configured to adjust the amount of variation in the second pressure signal based on an amount of boost provided to the engine during the second period.

7. The system of claim 3 wherein the controller is configured to determine the second threshold based on an amount of boost provided to the engine.

8. The system of claim 3 wherein the controller is further configured to control the duty cycle of the purge valve at a predetermined value during the second period.

9. The system of claim 3 wherein the controller is further configured to open a vent valve of the fuel system during the second period.

10. A method comprising:

detecting when an engine is started;

generating, using a pressure sensor, a first pressure signal indicating a first pressure within a fuel system of the engine when the engine is started and when a purge valve of the fuel system is closed;

determining an amount of variation in the first pressure signal over a first period;

determining a state of the pressure sensor based on the amount of variation in the first pressure signal over the first period;

determining that the pressure sensor operates normally if the amount of variation in the first pressure signal is less than a first threshold and that the pressure sensor is faulty if the amount of variation in the first pressure signal is greater than or equal to the first threshold; and

determining the first threshold based on a leakage rating of the purge valve,

wherein the leakage rating of the purge valve is non-zero.

11. The method of claim 10 further comprising determining the amount of variation in the first pressure signal based on a difference between a current pressure reading and a previous pressure reading, an absolute value of the difference between the current pressure reading and the previous pressure reading, and a running total of the absolute value of the difference between the current pressure reading and the previous pressure reading over the first period.

12. The method of claim 10 further comprising:

subsequently generating a second pressure signal indicating a second pressure within the fuel system when the purge valve of the fuel system is cycled at a duty cycle;

determining an amount of variation in the second pressure signal over a second period; and

diagnosing a fault associated with flow through the purge valve if the amount of variation in the first pressure signal is less than the first threshold and the amount of variation in the second pressure signal is less than a second threshold.

13. The method of claim 12 further comprising determining the amount of variation in the second pressure signal based on a difference between a current pressure reading and a previous pressure reading, an absolute value of the difference between the current pressure reading and the previous pressure reading, and a running total of the absolute value of the difference between the current pressure reading and the previous pressure reading over the second period.

14. The method of claim 12 further comprising determining the second threshold based on a predetermined relationship between a flow restriction in the purge valve and the amount of variation in the second pressure signal.

15. The method of claim 12 further comprising adjusting the amount of variation in the second pressure signal based on an amount of boost provided to the engine during the second period.

16. The method of claim 12 further comprising determining the second threshold based on an amount of boost provided to the engine.

17. The method of claim 12 further comprising maintaining the duty cycle of the purge valve at a predetermined value during the second period.

18. The method of claim 12 further comprising opening a vent valve of the fuel system during the second period.