Both the check engine light and service engine soon light are the same. Both are indicators that a vehicle's engine has identified an emissions related problem which might cause the engine to produce excessive emissions. If your vehicle's service engine soon light is on, it will fail the smog test. A smog check repair station should retrieve the trouble codes stored in the engine ECU (engine control unit) and use the code(s) to troubleshoot the emissions failure. Only after the fault(s) have been repaired and the service engine soon light turned off (reset) can the vehicle pass the smog inspection.
