Diesel owners also have the option of using a mobile inspection service. All diesel vehicles registered in Massachusetts, including trucks and buses, must get a safety test. Certain vehicles are exempt from the emissions test. The diesel emissions test uses a smoke opacity meter to measure the smoke from a vehicle's tailpipe. The darker the smoke, the greater the pollution and the higher the opacity reading.
All testing is done at licensed testing stations that have diesel inspection equipment.
If your vehicle fails the emissions test, your inspector will give you a Vehicle Inspection Packet that explains your options. You have 60 days to make the necessary repairs and pass a re-inspection. After repairs have been made, you are entitled to one free re-test within 60 days of the original test at the station where you had your first test. By law, safety defects must be repaired immediately at the repair facility of your choice. You are entitled to one free re-test within 60 days at the inspection station where your vehicle was originally tested.