To pass a smog test in California the car must not only pass emissions and systems checks. The Check Engine light must work when the key is turned on, and it must not be on with the engine running. Furthermore, the smog test includes scanning your engine computer (ECU) for Readiness Codes. Do not confuse these with the Diagnostic Trouble Codes (DTC). Readiness Codes are the results from the 8 emissions related self tests that your car’s computer performs each time you start and drive your car. In order, the Readiness Codes are: Exhaust Gas Recirculation, Oxygen sensor heating, Oxygen sensors, Air Conditioner, Secondary Air Injection, Evaporative Emissions System, Catalytic Converter Heating, and Catalytic Converter Status. These Readiness Codes are seen on our scan tools as a string of 8 bits, or Zeros and Ones. A Zero means the system passed, a One means the system failed. The smog test station wants to see 0000 0000.
There are many more diagnostic tests performed by all the computers that set the Diagnostic Trouble Codes (DTC), but these Readiness Codes are the checks of the emission systems related to a smog test. Whenever a repair has included clearing DTC’s, the Readiness Codes are all set to 1. The car must be driven for a while until all the driving conditions have been met for to perform the Readiness Tests before it will pass a smog test. Alternatively, on most cars, our technicians can manually run the Readiness Test procedures to set the Readiness Codes back to 0’s, then the car can pass a smog test immediately.