Exhaust gas treatment system including an enhanced SCR diagnostic unit

1. A controller for operating an exhaust gas treatment system included with an internal combustion engine, the controller comprising:

a stored sulfur module configured to determine an amount of sulfur in a selective catalytic reduction (“SCR”) device of the exhaust treatment system;

a SCR diagnostics module configured to monitor an efficiency of the SCR device and to indicate a failure of the SCR device when the efficiency of the SCR device falls below an efficiency diagnostics threshold; and

a desulfurization mode trigger module configured to configured to set a desulfurization request based one or more trigger conditions, including the amount of sulfur in the SCR device;

wherein an operation of the SCR diagnostics module is disabled if the amount of sulfur in the SCR device is above a first threshold to prevent a false indication of the failure of the SCR device.

2. The controller of claim 1 , wherein the efficiency diagnostics threshold of the SCR diagnostics module is scaled by a correction factor based on determining that the amount of sulfur in the SCR device is above a second threshold and below the first threshold.

3. The controller of claim 2 , wherein the correction factor is based on the amount of sulfur in the SCR device.

4. The controller of claim 1 , wherein in response to detecting desulfurization of the SCR device, the SCR diagnostics module is disabled.

5. The controller of claim 1 , wherein the operation of the SCR diagnostics module is disabled based on a frequency of regeneration of a particulate filter (“PF”) of the exhaust gas treatment being below a lower frequency threshold.

6. The controller of claim 5 , wherein the efficiency diagnostics threshold of the SCR diagnostics module is scaled by a correction factor based on determining that one or more of:

a frequency of regeneration of a particulate filter (“PF”) of the exhaust gas treatment being below a higher frequency threshold; and

the amount of sulfur in the SCR device being above a second threshold.

7. The controller of claim 5 , further comprising disabling the SCR diagnostics module in response to detecting a desulfurization of the SCR device.

8. A method for performing diagnostics of a selective catalytic reduction (“SCR”) device in an exhaust gas treatment system of an internal combustion engine, the method comprising:

monitoring an amount of sulfur in the SCR device of the exhaust treatment system;

monitoring, by an SCR diagnostics module, an efficiency of the SCR device and indicating a failure of the SCR device when the efficiency of the SCR device falls below an efficiency diagnostics threshold; and

executing a desulfurization on the SCR device based one or more trigger conditions, including the amount of sulfur in the SCR device;

based on determining that the amount of sulfur in the SCR device is above a first threshold, disabling an operation of the SCR diagnostics module to prevent a false indication of the failure of the SCR device.

9. The method of claim 8 , further comprising scaling the efficiency diagnostics threshold by a correction factor based on determining that the amount of sulfur in the SCR device is above a second threshold and below the first threshold.

10. The method of claim 9 , wherein the correction factor is based on the amount of sulfur in the SCR device.

11. The method of claim 8 , further comprising disabling the SCR diagnostics module in response to detecting desulfurization of the SCR device.

12. The method of claim 8 , further comprising disabling the operation of the SCR diagnostics module based on a frequency of regeneration of a particulate filter (“PF”) of the exhaust gas treatment being below a lower frequency threshold.

13. The method of claim 12 , further comprising scaling the efficiency diagnostics threshold by a correction factor based on determining that one or more of:

a frequency of regeneration of a particulate filter (“PF”) of the exhaust gas treatment being below a higher frequency threshold; and

the amount of sulfur in the SCR device being above a second threshold.

14. The method of claim 12 , further comprising disabling the SCR diagnostics module in response to detecting desulfurization of the SCR device.

15. A controller for operating an exhaust gas treatment system included with an internal combustion engine, the controller comprising:

a stored sulfur module configured to determine an amount of sulfur in a selective catalytic reduction (“SCR”) device of the exhaust treatment system; and

a SCR diagnostics module configured to monitor an efficiency of the SCR device and to indicate a failure of the SCR device when the efficiency of the SCR device falls below an efficiency diagnostics threshold; and

a desulfurization mode trigger module configured to configured to set a desulfurization request based one or more trigger conditions, including the amount of sulfur in the SCR device;

wherein an operation of the SCR diagnostics module is disabled if a frequency of regeneration of a particulate filter (“PF”) of the exhaust gas treatment is below a lower threshold to prevent a false indication of the failure of the SCR device.

16. The controller of claim 15 , wherein the efficiency diagnostics threshold of the SCR diagnostics module is scaled by a correction factor based on determining that the frequency of regeneration of the PF is above a lower threshold and below a higher threshold.

17. The controller of claim 16 , wherein the correction factor is based on the frequency of regeneration of the PF.

18. The controller of claim 15 , further comprising disabling the SCR diagnostics module in response to detecting a desulfurization of the SCR device.

19. The controller of claim 15 , wherein the operation of the SCR diagnostics module is disabled based on the amount of sulfur in the SCR device being above a first threshold.

20. The controller of claim 19 , wherein the efficiency diagnostics threshold of the SCR diagnostics module is scaled by a correction factor based on determining that one or more of:

a frequency of regeneration of a particulate filter (“PF”) of the exhaust gas treatment being below a higher frequency threshold; and

the amount of sulfur in the SCR device being above a second threshold.