Will my BMW pass smog? There's a light on...
Updated: Aug 30
Believe it or not, here at Driven SD we get this question quite often. And the answer is no. Not with that light on it won't, at least not in California. The dreaded "Check Engine" light or "Service Engine Soon" light. This light comes on when your car's engine computer (or DME in BMW lingo) thinks there is a problem that could affect, or is affecting, your car's emissions control system. This is one of the main things checked by the smog machine during a test. If it's on, it won't pass.
This light can come on for very many reasons. From a simple loose gas cap to an expensive engine or transmission failure.
What if I just clear the codes?
You could, but... if the failure is permanent (like a bad sensor or shorted wiring) the fault code will come back pretty quickly, if not instantly. If it's an intermittent issue the fault may stay away, however your engine computer is really smart.
When you clear the fault codes out the computer also resets what are called "readiness monitors". These are system test that the computer runs. The purpose of readiness monitors is to self-test the car’s emission control systems. If the monitors are not set, you won't pass smog. Here's a list of the monitors:
Comprehensive Component (malfunctions in any powertrain electronic component or circuit that provides input or output signals to the computer that can affect emissions and is not monitored by another OBD II monitor.)
Spark ignition vehicles (Gas)
Evaporative (EVAP) System
Secondary Air System
Oxygen (O2) Sensor
Oxygen Sensor Heater
EGR (Exhaust Gas Recirculation) and/or VVT System
Compression ignition vehicles (Diesel)
Exhaust Gas Sensor
EGR and/or VVT System
That's a lot of stuff!
So, what should I do?
You could check codes with a scanner and get lucky putting parts in the car, but from our experience this usually turns into a waste of time and money. Your best bet is to get the car properly diagnosed by a professional.
Schedule your BMW to get diagnosed properly at Driven SD and we'll get your faults fixed, monitors set and ready to pass smog.