System and method for diagnosing a fault in an oxygen sensor based on ambient temperature

1. A system comprising:

an error count module that increases an error count when an actual air/fuel ratio generated by an oxygen sensor monitoring an exhaust system of an engine is different than a desired air/fuel ratio, and that selectively adjusts a rate at which the error count is increased based on an ambient temperature;

a sensor diagnostic module that diagnoses a fault in the oxygen sensor when the error count is greater than a first predetermined count; and

an actuator control module that controls an actuator of the engine based on whether a fault in the oxygen sensor is diagnosed.

2. The system of claim 1 further comprising a multiplier module that determines a multiplier based on the ambient temperature, wherein the error count module selectively applies the multiplier to the error count to adjust the rate at which the error count is increased.

3. The system of claim 2 wherein the multiplier module increases the multiplier as the ambient temperature decreases, and the multiplier module decreases the multiplier as the ambient temperature increases.

4. The system of claim 2 wherein the error count module selectively applies the multiplier to the error count when a ratio of an actual engine speed to a desired engine speed is less than a first predetermined value.

5. The system of claim 4 wherein the multiplier module determines the multiplier further based on the ratio of the actual engine speed to the desired engine speed.

6. The system of claim 4 wherein the error count module applies the multiplier to the error count when the error count is greater than a second predetermined count, wherein the second predetermined count is less than the first predetermined count.

7. The system of claim 6 wherein the error count module stops applying the multiplier to the error count when the ratio of the actual engine speed to the desired engine speed is greater than a second predetermined value, wherein the second predetermined value is greater than the first predetermined value.

8. The system of claim 1 wherein the error count module increases the error count when the actual air/fuel ratio is rich and the desired air/fuel ratio is lean.

9. The system of claim 1 wherein the error count module increases the error count when the actual air/fuel ratio is lean and the desired air/fuel ratio is rich.

10. The system of claim 1 wherein the error count module sets the error count to zero when the actual air/fuel ratio and the desired air/fuel ratio are one of rich and lean.

11. A method comprising:

increasing an error count when an actual air/fuel ratio generated by an oxygen sensor monitoring an exhaust system of an engine is different than a desired air/fuel ratio, and that selectively adjusts a rate at which the error count is increased based on an ambient temperature;

diagnosing a fault in the oxygen sensor when the error count is greater than a first predetermined count; and

controlling an actuator of the engine based on whether a fault in the oxygen sensor is diagnosed.

12. The method of claim 11 further comprising:

determining a multiplier based on the ambient temperature; and

selectively applying the multiplier to the error count to adjust the rate at which the error count is increased.

13. The method of claim 12 further comprising:

increasing the multiplier as the ambient temperature decreases; and

decreasing the multiplier as the ambient temperature increases.

14. The method of claim 12 further comprising selectively applying the multiplier to the error count when a ratio of an actual engine speed to a desired engine speed is less than a first predetermined value.

15. The method of claim 14 further comprising determining the multiplier further based on the ratio of the actual engine speed to the desired engine speed.

16. The method of claim 14 further comprising applying the multiplier to the error count when the error count is greater than a second predetermined count, wherein the second predetermined count is less than the first predetermined count.

17. The method of claim 16 further comprising stopping application of the multiplier to the error count when the ratio of the actual engine speed to the desired engine speed is greater than a second predetermined value, wherein the second predetermined value is greater than the first predetermined value.

18. The method of claim 11 further comprising increasing the error count when the actual air/fuel ratio is rich and the desired air/fuel ratio is lean.

19. The method of claim 11 further comprising increasing the error count when the actual air/fuel ratio is lean and the desired air/fuel ratio is rich.

20. The method of claim 11 further comprising setting the error count to zero when the actual air/fuel ratio and the desired air/fuel ratio are one of rich and lean.