The EPA fact sheet entitled, “If Your Car Just Failed An Emissions Test...You May Be Entitled To Free Repairs” (8 pp., 23 KB, about PDF ) provides the following question and answer:
Q. “Does the Warranty Cover Parts That Need Replacement Under Scheduled Maintenance?”
A. “Parts with a scheduled replacement interval that is less than the length of the warranty, such as "replace at 15,000 miles or 12 months" are warranted up to the first replacement point only. Parts with a maintenance instruction that requires them to be "checked and replaced if necessary," or any similar requirement, receive full coverage under the warranty. Note, though, that if you fail to check a part when you are instructed to and that part causes another part to fail, the second part will not be covered cause your malmaintenance caused the failure”.
You may also want to read the following resources which provide information on emissions warranties:
- Emissions Warranties for 1995 and Newer Cars and Trucks
- 40 CFR 1037.120 - Emission-related Warranty Requirements (2 pp, 218 KB, About PDF)