Minor oil leaks which are not immediately detectable, i.e. a small oil leak spot when the vehicle is parked overnight, should not effect the smog check. If the oil leak is so bad that it's causing drivability problems, such as an internal oil leak (oil entering combustion chambers), then yes, the smog test could be effected either due to high exhaust emissions or smoke trouble; part of the smog check inspects for smoke being emitted from the exhaust and/or under the hood.
If your car has an external oil leak, such as from the engine oil pan or valve cover gasket (perhaps even the transmission) and it is severe enough, the smog technician may refuse to inspect your vehicle or, if during the smog test the oil leak(s) become apparent and effect the testing procedures, the technician can decide to abort the test, in which case you may be responsible for the inspection fee without obtaining a completed smog inspection.
In short, yes, an oil leak can cause your vehicle to fail the smog inspection, but it depends on the severity of the leak, its location, and smog technician discretion.
posted by SmogTips Support 07-17-2018 07:32 AM