Subaru vehicles pass California smog reliably when the engine is healthy, but the horizontally-opposed (boxer) EJ25 engine used in 2006-2014 Outbacks, Foresters, and Legacys has a well-documented head gasket failure mode that causes combustion leaks and emissions failures.
- EJ25 2.5L naturally-aspirated engine (2006-2014 Outback, Forester, Legacy, Impreza): external head gasket seepage is cosmetic, but internal combustion gas leakage affects coolant combustion and raises HC emissions
- Internal head gasket failure causes white exhaust smoke and elevated hydrocarbon readings — a reliable smog fail indicator
- EJ257 2.5L turbocharged (WRX, STI 2004-2021): oil consumption via turbocharger and valve guides; fouled O2 sensors and catalyst contamination on high-mileage examples
- FA20DIT (BRZ, WRX 2013-2021): direct-injection; moderate carbon buildup risk at 80,000+ miles, though port-injection assist on some models reduces it
- FB25 and FB20 engines (2012+ non-WRX/STI): significantly improved over EJ25 — head gasket failure is rare, smog compliance strong
- Crosstrek hybrid and Outback XT 2.4T (2020+): newer turbocharged engines with strong emissions records and no documented systemic smog issues
Per BAR inspection data and Subaru TSB/service manual guidance.