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Smog Check Repair

Will a bad or broken muffler cause a car to fail smog test?

My cars muffler is beginning to fail, starting to get louder than normal, and I think it has holes in it. I need to pass a smog inspection in August. Should I replace the muffler before I get a smog test or is there a chance that the failing muffler won't cause my car to fail the emissions test?

Thanks for your input!


The smog test does not test the muffler but... we don't recommend you take your car in for testing if you can tell it's fails; either due to loud noise coming from it or if it has large holes or cracks in it. At best, it may cause the smog technician a problem with the emissions tailpipe probe, or dilute your vehicle exhaust to the point the smog machine will not allow the smog technician to even begin the smog check.


If the muffler is intact but has holes consider this: Smog machines are calibrated in California (every three days) and are designed not to allow the testing of vehicles which emit oxygen levels exceeding the smog machines preset limits. If the holes on a muffler were large enough to where fresh air would be vacuumed into a car's exhaust stream, the test results would be incorrect, and the smog machine may not even allow the smog inspection to begin or continue. Worst case scenario would be the smog test begins, and is aborted halfway. You'd be required to pay the smog inspection fee, without getting smog check results or a smog check certificate. We have to recommend you get the muffler replaced before the smog test.


Also consider this... If there are no visible holes or cracks on the muffler, and it is only loud, there is the possibility that there is an internal blockage due to material break down. The blockage will cause a restriction in exhaust flow. Restricting the exhaust flow will most definitely cause your vehicle to operate under stress, causing increased emissions across the board. We'd recommend, if it's not expensive, go ahead and get it fixed before the smog test. You'll end up saving time.

posted by SmogTips Support 06-02-2010 06:50 PM

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