Minimum power consumption for cool down diagnostic based on cylinder deactivation

1. A diagnostic system for an engine of a vehicle, comprising:

a temperature determination module that receives an indication of whether one or more cylinders within the engine are deactivated, that sets a first temperature threshold based on a first predetermined temperature when the indication indicates that zero cylinders of the engine are deactivated, and that sets the first temperature threshold based on a second predetermined temperature when the indication indicates that one or more of the cylinders of the engine are deactivated, wherein the first predetermined temperature is greater than the second predetermined temperature;

a comparison module that selectively determines whether a temperature of engine coolant is less than the first temperature threshold;

a fault indication module that diagnoses a fault in response to the comparison module determining that the temperature of the engine coolant is less than the first temperature threshold; and

a remedial action module that selectively adjusts at least one engine operating parameter to increase the temperature of the engine coolant in response to the fault indication module diagnosing the fault.

2. The diagnostic system of claim 1 further comprising a cylinder control module that receives an instruction to deactivate a predetermined number of cylinders within the engine and that selectively deactivates at least one cylinder within the engine based on the instruction.

3. The diagnostic system of claim 2 wherein the cylinder control module generates the indication based on the predetermined number of cylinders.

4. The diagnostic system of claim 1 wherein the remedial action module further activates a malfunction indicator in response to the fault indication module diagnosing the fault.

5. The diagnostic system of claim 1 further comprising a disabling module that disables the comparison module until the temperature of the engine coolant is greater than a second temperature threshold.

6. The diagnostic system of claim 5 wherein the disabling module disables the comparison module for a predetermined period in response to a fuel cutoff event ending.

7. The diagnostic system of claim 5 wherein the disabling module disables the comparison module in response to i) a determination that the temperature of the engine coolant is greater than the second temperature threshold and ii) a determination that a power produced by the engine is less than a predetermined power.

8. The diagnostic system of claim 7 wherein, in response to a determination that the power produced by the engine is greater than the predetermined power, the disabling module disables the comparison module for a predetermined period.

9. A diagnostic method for an engine of a vehicle, comprising:

receiving an indication of whether one or more cylinders within the engine are deactivated;

setting a first temperature threshold based on a first predetermined temperature when the indication indicates that zero cylinders of the engine are deactivated;

setting the first temperature threshold based on a second predetermined temperature when the indication indicates that one or more of the cylinders of the engine are deactivated,

wherein the first predetermined temperature is greater than the second predetermined temperature;

determining whether a temperature of engine coolant is less than the first temperature threshold;

diagnosing a fault in response to the determination that the temperature of the engine coolant is less than the first temperature threshold; and

selectively adjusting at least one engine operating parameter to increase the temperature of the engine coolant in response to the diagnosis of the fault.

10. The diagnostic method of claim 9 further comprising receiving an instruction to deactivate a predetermined number of cylinders within the engine and selectively deactivating at least one cylinder within the engine based on the instruction.

11. The diagnostic method of claim 10 further comprising generating the indication based on the predetermined number of cylinders.

12. The diagnostic method of claim 9 further comprising activating a malfunction indicator in response to the diagnosis of the fault.

13. The diagnostic method of claim 9 further comprising disabling the determination of whether the temperature of the engine coolant is less than the first temperature threshold in response to a determination that the temperature of the engine coolant is greater than a second temperature threshold.

14. The diagnostic method of claim 13 further comprising disabling the determination of whether the temperature of the engine coolant is less than the first temperature threshold for a predetermined period in response to a fuel cutoff event ending.

15. The diagnostic method of claim 9 further comprising disabling the determination of whether the temperature of the engine coolant is less than the first temperature threshold in response to i) a determination that the temperature of the engine coolant is greater than a second temperature threshold and ii) a determination that a power produced by the engine is less than a predetermined power.

16. The diagnostic method of claim 15 further comprising disabling the determination of whether the temperature of the engine coolant is less than the first temperature threshold for a predetermined period in response to a determination that the power produced by the engine becomes greater than the predetermined power.

17. The diagnostic method of claim 9 wherein selectively adjusting at least one engine operating parameter to increase the temperature of the engine coolant in response to the diagnosis of the fault includes retarding spark timing in response to the diagnosis of the fault.

18. The diagnostic system of claim 1 wherein the at least one engine operating parameter includes spark timing, and the remedial action module retards the spark timing in response to the diagnosis of the fault.