We'd recommend first pulling the trouble code stored in the ECU (engine control unit) when the check engine light is on. You'll need an OBD-II trouble code scanner to do so. Locate your vehicle's OBD II DLC (data link connector - usually located drivers side under the dashboard and near the interior fusebox), and retrieve the trouble code(s). Ensure a trouble code relates to the fuel sending unit. The sending unit is the sensor (located inside the gas tank) which relays fuel level information to the ECU, which in turn sends a signal to the fuel gauge on the dashboard to move the needle. If the sending unit fails or is defective, it will cause the check engine light to illuminate, and yes, it will cause a smog check failure... automatically.
You might be thinking, I'll take the test when the light is off... there's a very slight chance of passing. If you obtain the smog test while the check engine light is off, there is a chance you may or may not pass the inspection, depending on whether all the Emission Readiness Monitors are complete or not. If the sending unit is defective, more than likely it will not allow one or more of the readiness monitors to run. Without all monitors complete, except the EVAP, a 2000 and newer vehicle can not pass the smog inspection. On a 1999 and older vehicle, any one monitor being in-complete is allowed.
Emission Monitors are internal computer self-tests which verify the operation of various engine emission systems.
posted by SmogTips Support
