Bad Catalytic Converter Symptoms

Once they start happening to your car, it’s not too difficult to spot bad catalytic converter symptoms. This little muffler look-alike is part of the car’s entire exhaust system. It works with the engine which expels gases that are dangerous for the environment and people as well. It takes these dangerous gases and converts them into gases that are less harmful. It turns hydrocarbons and carbon monoxide into the must less harmful substances of water vapor and carbon dioxide. But should the unit begin to fail, it will not be difficult to spot the these symptoms.


Some of the other signs that the catalytic converter has failed or is failing are that you may hear a rattle noise under the car. Many time when a catalytic converter fails it breaks apart and rattles inside if the housing. In some cases you may actually pieces of the converter exit the exhaust system. Sometimes those same pieces can cause the exhaust system to clog or become restricted. In that case you might notice a loss in performance. If the car is OBD II compliant, you will usually see the “Check Engine” light appear on the dash board. There may be other indications but these are some of the most common.



When it is working perfectly, this little catalyst simply changes gases as they pass through and are converted only to be expelled through the exhaust pipe of the vehicle. But a faulty unit will begin to affect the performance of the car. It will begin to show you signs that there is something going on with the unit. The trouble is that when it fails to work properly the harmful gases are then being released back out into the atmosphere unchanged. This is why it is important to identify symptoms of bad catalytic converter. This way you can get it replaced in a timely fashion.


Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gasgasoline/petrol, diesel fuelfuel oil or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipeflue gas stack or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume.




There are basically three things that may happen to your car to let you know there is a problem. The first thing is that you may notice that your car doesn’t accelerate with as much power as it did before. It feels like you are trying to drive your car into a real strong headwind and just cannot get ahead of it. This is usually a sign that the catalyst has become plugged. It may be caused by faulty sparkplugs or an exhaust valve that has been burned.


The catalytic converter can plug up and cause those symptoms.


The converter can be tested by doing a back pressure test. If the converter is totally plugged it will get almost red after driving a while (very hot). Also exhaust will be restricted out of the tail pipe. Another way to test it is to tap on it and listen for an internal rattle.


Some actually cause a rotten egg smell.


If you have a check engine light, get the ECM scanned to find out what fault code are stored. Check fuel pressure, check all the spark plugs. All of those can cause hesitation if faulty.



You may smell a foul odor coming from the exhaust. This is a sign that the fuel mixture is too rich and is not burning properly but working to plug the unit instead. You may also notice that all of a sudden you are not getting the gas mileage that you are used to. If you notice a real quick drop in the fuel efficiency of your car it may be one of the main symptoms.


So why does it smell?  That’s a good question.  The short answer is that all gasoline contains a small trace of sulfur.  When the exhaust stinks of rotten eggs, it is because the catalytic converter is being flooded with fuel and the amount of sulfur passing through has increased dramatically. Your catalytic converter is being overworked or cooked.  What you now smell is large amounts of bad air being converted (to help reduce emissions) at a very high rate (far greater than the recommended 3%), hence the high concentration of sulfur.  The catalytic converter is actually doing its job, but not for long.  A melt down will soon occur because of the tremendous amount of heat being generated by the excessive chemical reaction – think of the heat generated by lighting a match.



The last sign is that the car will fail its emissions test. Inspectors can usually tell first of all by the color of the smoke that is emitted from the exhaust.


The federal Clean Air Act mandates the operation of vehicle emission inspection and maintenance programs in areas throughout the nation with significant air quality issues, including Southeastern Wisconsin. In addition to identifying vehicles violating state emission standards, the Wisconsin Vehicle Inspection Program (WVIP) also identifies vehicles with tampered emission control equipment. The owners of these vehicles are required to have tampered items repaired, replaced, or otherwise returned to proper working order.

Motor vehicles are a major source of air pollutants in metropolitan areas. Vehicle exhaust contains carbon monoxide and other pollutants – volatile organic compounds and nitrogen oxides – that react to form ground level ozone. Motor vehicles emit about one-third of Southeastern Wisconsin’s volatile organic compounds (mostly hydrocarbons) and about 60% of its carbon monoxide.



These are some of the bad catalytic converter symptoms you should know.