Air filter
Replace the air filter on schedule or when the restriction indicator says so. Dusty roads shorten its life. Do not run without it, and make sure the housing seals.
DEF basics
- Use DEF certified to the industry standard (API certified). Do not dilute it.
- Keep it clean: dirt and other fluids contaminate DEF and damage the system.
- Store it out of direct sun and extreme heat, and keep the cap tight.
- Newer engines have a DEF filter on the Cummins schedule.
Where this comes from
- Cummins: DEF quality and maintenance (PDF)
- API: DEF do's and don'ts fact sheet (PDF)
- Cummins: Motorhome quick reference guide, B6.7 / ISB (PDF)
- Cummins: Diesel RV engine operation and maintenance presentation (PDF)
Last reviewed 2026-10-19. General information only: your owner's manual and service information come first.