Why did car fail smog check?

Red Phone: Low branches need to be cut

“I had my car smogged recently. Apparently it didn’t pass with them because the check engine light wasn’t turning on. The guy said that his machine checked it and it failed three times. When I took the car to a second location, it passed no problem. I mentioned about the machine the other guy was using. He said it doesn’t take a machine to check the engine light. You have to do it manually. You have to turn the key yourself and see if the check engine light comes on. I was wondering if it takes a machine to see the check engine light or if it is done manually.”

Red Phone: Dear Lit Up, Not knowing the difference between fog and smog, Red Phone forwarded your question to smogtips.com, an online forum that specializes in smog related questions. Here is their response:

“On all OBD II vehicles (1996 and newer), both the smog machine and the smog technician will inspect the Check Engine light. The smog machine will check to make sure the Check Engine light is not on during the smog test, and the smog technician will turn the ignition key to the ‘on’ position and observe the Check Engine light is illuminated. The technician’s visual observation will be entered into the smog machine manually.”

So it appears the answer is yes, and yes. On newer cars, the check engine light portion is done both manually and by computer. But the smog machine is only used for vehicles 1996 or newer, so it is possible there was confusion by one of the technicians depending on when your car was made or perhaps he doesn’t fully understand how a smog test is done.

The State of California requires smog inspections to be completed in three stages. During an emissions test, the tester will drive the car and measure emissions emitted from the tail pipe. During the visual inspection, inspectors are required to manually inspect emissions systems to make sure they are in working order and haven’t been altered. And during the functional tests, the timing, exhaust gas recirculation (EGR) and check engine light are inspected. Any emissions defects found during this stage are considered unhealthy for the air and cause the car not to pass.

Also as a side note, if your check engine light is on when you take your car to get smogged, the test will automatically fail. Some people have also advised making sure a car is tuned up, the oil is changed, the tire pressure is correct and the car is warmed up for 15 minutes before the inspection to give it the greatest chance of passing.

To see the full requirements of a smog check, visit smogtips.com/passing_inspection.cfm.

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