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.

Catalytic Converter Replacement $291.63 - $3224.07 Get a Quote
Exhaust System Inspection $79.99 - $99.99 Get a Quote

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

Hello, do you know how much it costs to fixed a damaged axel on a 2005 Hyundai Elantra?

At auto parts stores, the axle costs roughly $70 on up. It takes about 1 to 2 hours to install the axle. The job requires special tools though and to ensure a trouble free result, the axle output seal in...

Bought new tire and value stem week later svc tire monitor light came on

The TPMS will need to be checked to see if the new sensor is not working or there is another sensor failure. you may have a low tire or failed sensor. Once the system is checked again the if the...

Transmission shifter won't shift into any gear.

Hi there. Go under the vehicle and check the slave cylinder to your clutch system. The cylinder may be leaking causing the pedal to be spongy and not able to become firm due to excessive air in the system. Check...

I have an oil leak in Chevy Suburban 2001. What would it cost to replace the oil pan gasket or timing cover gasket?

Sent billing question to CS for cost to replace the oil pan gasket or timing cover gasket.

AC compressor failure

Hello. Yes, all of the things listed are usually recommended when replacing an AC compressor. AC systems are very sealed and pressurized, and taking the precaution to replace the associated components helps prevent any premature failure's of any sort. The...

Brake pads replaced but still feel soft

It sounds like your 2006 Freestar does have a legitimate brake issue and the mechanics you are currently going to have not identified it. You need to have confidence that your brakes are "working as designed" and will stop your...

Should I buy a car that has been sitting for 7 years, it ran when he got it

Only if you are prepared to replace the entire fuel system, tires, brakes, cooling system, and belts. These systems may be bad after sitting for that long of a period. Other issues could include the A/C and some other systems...

Replacing transmission on '95 Toyota Corolla with Celica transmission

You shouldn't just be swapping those things because it's a different engine, different size, and different gear ratio in them. Just live with whatever it does because you really shouldn't be doing these types of swap. I know guys who...

Getting multiple trouble codes

This is a strange group of codes that you have. Most of the time when you get this number of different codes coming up it is due to a voltage issue or a module that is failing. When something like...

Related articles

The Best Used Cars to Buy If Safety is #1
Maybe Maybe you’re a parent buying the first car for your teenager, or perhaps you’re a new parent and the safety of your little one is of the utmost importance. Or perhaps you're a safety-minded individual looking to make a...
How to Buy a Good Quality Exhaust Manifold
The The exhaust manifold bolts to the cylinder head of the engine and pulls exhaust gases from the individual ports; combining them into one outlet to flow back into the remainder of the exhaust system. Exhaust fumes are sneaky, and...
5 Red Flags That Your Car Needs Immediate Attention
It It isn’t popular to think about, but you should be prepared for vehicle problems. Vehicles are designed and built by people, and they are only as perfect or flawed as the people who build them. That means sooner or...