What to know — Diesel smog rules in California
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.
About Diesel Smog Check at San Diego STAR Smog Check
Specialized diesel smog check performed at San Diego STAR Smog Check, our San Diego location.
Visit us for diesel smog check
- Address: 2484 F St Suite A, San Diego, CA 92102
- Phone: (619) 257-2838
- Website: https://www.smogtestinsandiego.com/
- Hours: Mon-Fri 8 AM – 6 PM · Sat 8 AM – 4 PM
What we do
- California-required smog inspection
- OBD-II readiness verification
- Same-day electronic DMV certificate filing
- Walk-ins welcome (no appointment needed)
- Bilingual English / Spanish service
*Regenerated 2026-05-25 from GBP-verified canonical data.*