Here are five signs that something may be wrong with your catalytic converter:
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Your vehicle’s fuel efficiency suddenly drops.
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Your vehicle doesn’t accelerate when you step on the gas pedal.
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Your vehicle fails an emissions test.
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The MIL or Check Engine light comes on.
The most common cause of failure in a catalytic converter in an older car is that it becomes so clogged that the exhaust gases can’t get through it to the muffler and out of the car. (If air can’t get out the rear of the vehicle, it can’t come in the front end, so the engine dies because no air is coming in to form the fuel/air mixture.)
Every car sold in the United States since 1996 has had an OBD (On-Board Diagnostic) II system that tests the catalytic converter (among many other things). If the unit allows too much pollution to escape from the tailpipe, it illuminates the MIL and produces a trouble code that can be read by a technician with what’s called a “scan tool.”
The catalytic converter is sensitive to changes in the contents and temperature of the exhaust gases, so another possible cause for failure is if the cylinder head gasket is damaged, allowing oil or coolant to get into the combustion chamber and be burned in the cylinders. Also, if your ignition system isn’t operating properly, unburned fuel in the exhaust gases can cause the catalytic converter to wear out or break down. This is another good reason for going for tune-ups at specified intervals!