What should I know about Mercedes-Benz smog checks in California?

Mercedes-Benz gasoline vehicles pass California smog reliably. Diesel BlueTec and CDI models require a fully intact AdBlue/DEF and SCR system — tampering with those components causes an automatic fail on visual inspection and OBD.

• BlueTec diesel models (ML350, GL350, E350, Sprinter): AdBlue/DEF tank and SCR catalyst must be intact; aftermarket deletes of DEF system are visible at inspection and detectable via OBD
• OM642 V6 diesel (Sprinter, ML320 CDI, GL320 CDI): EGR cooler failures are common; faulty EGR causes fault codes and potential readiness failures
• Sprinter 2500/3500 (both diesel and gas): frequent fleet vehicle; fleet accounts with consolidated billing available
• M272/M273 V6/V8 gasoline engines (C/E/S-Class 2005-2012): balance shaft and timing chain wear on high-mileage examples can cause timing codes affecting readiness
• Newer AMG 4.0L biturbo V8 (C63, E63, GLE63 2015+): direct-injection; moderate carbon buildup risk; strong emissions compliance overall
• EVAP system on C-Class and E-Class sedans has small purge valve and gas cap leak sensitivity — a common source of P0442 codes on older models

Per BAR inspection data, CARB diesel emissions rules, and Mercedes-Benz TSB documentation.