Every California smog check term and question, plainly defined
What does a diesel smog check involve in California?
1998 and newer diesel vehicles at or under 14,000 lbs GVWR require California smog inspection using OBD-II scan plus a visual check of all emissions control equipment.
Diesel Particulate Filter (DPF) must be present and unmodified — removal is an automatic fail on visual inspection and OBD
Exhaust Gas Recirculation (EGR) system must be intact; deleted EGR triggers fault codes and visible fail
Diesel Exhaust Fluid (DEF) system on 2010+ diesel vehicles must be functional; limp-mode from DEF faults equals automatic fail
Opacity (visible smoke) test is performed — excessive black or blue smoke is grounds for rejection
Aftermarket tuners that alter emissions calibration are prohibited; OBD scan reveals tuner presence
Deleted emissions equipment can be restored before testing — some test+repair shops offer OEM restoration
Per BAR diesel inspection criteria and CARB diesel emission control device rules.