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Even newer cars fail smog check as they age

Today's cars are very efficient. The technology used to monitor and adjust engine functions is pretty amazing. Like other Jackson County drivers, I get my smog check as required, and my cars always pass. With this in mind, I'm wondering if there are any data or reports that show what percentage of cars pass and fail and their age. Are we nearly to a time when this test is unnecessary for new cars?

— Tom, Eagle Point

You're in a little bit of luck, Tom. There is data that show what percentage of cars pass and fail — broken down by model year — provided courtesy of Doug Hatfield, manager of the vehicle inspection program at the Oregon Department of Environmental Quality.  

Hatfield provided us with statewide figures for vehicle inspections in Oregon that occurred in the calendar year 2014, and of the 524,991 vehicles tested in Medford and the Portland metro area, only 34,485 vehicles manufactured between 1975 and 2010 model years didn't pass, a failure rate of 6.57 percent.

"That low overall failure rate can, in part, be attributed to the technology of newer vehicles," Hatfield wrote in an email response. "However, as vehicles age, even these more sophisticated, cleaner cars fail more frequently."

Because it sounds like you own late-model cars, you've probably noticed that your inspection involves a technician plugging equipment into the vehicle's on-board diagnostic or "OBD" port. All vehicles manufactured since the 1996 model year are equipped with OBD systems, and are tested this way to verify the engine's oxygen sensors, catalytic converter and other systems are working properly.

Unfortunately, the test isn't unnecessary. Vehicles made after 1996 don't always work properly.

"The OBD system controls and monitors many emissions components such as oxygen sensors and catalytic converters," Hatfield said. 

Hatfield broke down that 2014 report by vehicle year, and '96 passenger cars and trucks (the first complete fleet of "modern" vehicles with OBD diagnostics), showed a failure rate of 10.98 percent on 17,027 vehicles tested. Similarly, '97 vehicles showed a 11.13 percent failure rate on 17,294 cars and trucks tested.

Cars manufactured after 1996 are equipped with a "Check Engine" light on the dashboard to indicate if there's a problem that would prevent the vehicle from passing inspection.

"When such components begin to malfunction, the "Check Engine" light illuminates on the dashboard," Hatfield said. "If DEQ's computer system in the DEQ Clean Air Station recognizes that (the Check Engine light) has been commanded on, the vehicle will fail the emissions test."

Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to youasked@mailtribune.com. We’re sorry, but the volume of questions received prevents us from answering all of them.

2014 Oregon DEQ Vehicle Inspection Report by Mail Tribune