Diesel vehicles have unique inspection requirements in Pennsylvania. Understanding these differences helps diesel owners prepare properly.
Diesel Emissions Requirements
Light-Duty Diesel (Under 8,500 lbs GVWR)
Light-duty diesel vehicles in emissions counties must pass OBD-II testing, same as gasoline vehicles (1997+).
Heavy-Duty Diesel (8,500+ lbs GVWR)
Heavy-duty diesel vehicles require opacity testing, which measures visible smoke emissions.
Understanding the Opacity Test
- Pass threshold: 40% opacity maximum for most vehicles
- Newer vehicles (2007+): 20% opacity maximum
- Test method: Snap acceleration while measuring exhaust
DPF (Diesel Particulate Filter)
The DPF is inspected for presence, condition, and warning lights. DPF deletes are illegal and will fail inspection.
Common Diesel Inspection Failures
- DPF delete: Removed particulate filters fail immediately
- EGR deletes: Modified emissions systems fail
- Excessive smoke: Failed opacity test
- DEF system errors: Low fluid or system faults
Diesel Inspection Costs
- Light-duty diesel: Same as gasoline ($35-60 total)
- Heavy-duty diesel: $40-75 (opacity testing adds cost)