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Forum > Failed Smog Test > Question

Failed Smog Check at 15 MPH but Passed at 25 MPH, Why?

Does the fact that my car failed at one speed but not the other give you any clues? Does the circumstance that the technician had the car running at idle for a long time and the engine temperature rising in the mean time to above normal have any bearing on this result? Thank you for any input you may have.

Answer:

While a vehicle is being tested at 15mph, the load placed on the engine is twice as high as during the 25mph test. The additional load causes the engine to put out more emissions than at 25 mph. A vehicle idling for a long period of time prior to the smog test should not cause an emissions failure unless the vehicle has emission related borderline faults; requiring manipulation of the smog check process in order to pass the test. posted by SmogTips Support

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