Q: Can a bad muffler cause a smog test to fail?

asked by on October 03, 2016

I just acquired my van and was told that it needed a catalytic converter and it failed the last smog test, it was a friends, so I believed them. Now, I thought to look under the van due to increased noise I believed was coming from muffler and was correct. Muffler is rusted in all the seams and small holes in the non seamed places. Is this why it failed smog and not the cat? I have purchased a new muffler, but should I buy a new car too, all must be welded, not bolted and is going to cost me $120, don't want to do 2x and must pass smog. Thanks so much!

My car has 160000 miles.
My car has an automatic transmission.

Hello. You need to see why the last smog failure was for. If the failure was excessive O2 in the exhaust test, then it could be the muffler. If it is for high HC or CO then it may be an engine running too rich or a converter issue. You will need to have the engine tested to see if the engine and converter have problems. If the converter is broken apart inside, then replace it anyway. If you need help with this, a certified professional from YourMechanic can come to your home or office to diagnose the system and pinpoint the appropriate repair.

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