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Failed smog test? It’s your cat’s fault!

Written by maryp posted on Friday, May 16th, 2008

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Whoa! Your BMW failed the smog test and now you are worried that, “you might need a catalytic converter”.

A catalytic converter rarely fails on a car that has been maintained properly. If it did fail, why? There is usually a problem that is the precursor of the “cat” failure. They usually do not just “stop” (as is the case with some electrical components). There is something else going on in the emission system in front of the cat that is usually the culprit.

An incorrect fuel mixture can actually cause the catalyst to begin to melt. That is some pretty unbelievable heat! So if you hear the term that your “catlyst is noisy”, or “rattling”, it’s an indicator that internal pieces have come apart. Faulty injectors, faulty oxygen sensors, worn plugs and/or plug wires could also cause a cat to fail. Any situation that would cause deposits in the ceramic unit and and restricts air flow could lead to a more serious problem. Restricted air flow can create excessive heat in your engine and you know where that is going……(and it’s not pretty).

So, hopefully, you don’t need a catalytic converter. Maybe it is just a spark plug that caused you to fail the Smog Test. Remember that it’s not only “just a good idea” to have a licensed Smog Check Tech working on your emission system. It is one of the Bureau of Automotive Repair Regulations in California. If you fail a Smog Test, the repair is to be done by a licensed Smog Technician. Even if you have any emission related issue, the repair is supposed to be done by a licensed Smog Tech at a licensed Smog Check Station, Test and Repair Shop. Help clean the air, by keeping your BMW maintained and you probably will never have to worry about that catalytic converter!

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