What is a catalytic converter and why do they fail? 

 

Gasoline engines are fueled with two chemical compounds: gasoline and air. Gasoline is made of two basic elements: hydrogen (H2) and carbon (C). In the form of gasoline, these two chemicals combine to make what we call a hydrocarbon (HC). Air is made up of two basic elements: oxygen (02) and nitrogen (N2).

 

If gasoline engines burned their fuel as efficiently as possible, they would produce three by-products: water vapor (H20), carbon dioxide (C02), nitrogen (N2).

 

For the most part, these chemical compounds are not harmful but they are not the only gasses in the exhaust emissions.   H20, C02, and N2 are the most desirable by-products of combustion, and automotive engineers strive to create emission control systems that allow a vehicle to produce only these three chemical groups.

 

Unfortunately, engines don't run perfectly and as a result they also produce three by-products commonly referred to as the "terrible trio" of automotive pollutants. This trio includes the following: carbon monoxide (C0), unburned hydrocarbons (HC), and oxides of nitrogen (NOx).

Carbon monoxide (CO) is an odorless, tasteless, poisonous gas that can cause a variety of health problems, and even death. Many urban areas experience critically high levels of carbon monoxide, especially during the cold winter months when engines take longer to warm up and run cleanly.

 

With the goal of cleaning the exhaust emissions, all auto manufacturers use catalytic converters on gasoline powered vehicles and since the late 1990’s on diesel powered cars and trucks to eliminate the harmful gasses.

 

The catalytic converter is a canister (sometimes more than one) that is located in the exhaust system and is filled with a ceramic material that is coated with precious metals that perform a “catalytic” reaction with the exhaust gasses to “convert” them from a pollutant form to a more benign, less polluting, gas.

 

The state of California has been a leader in requiring the use of catalytic converters since their original designs in the mid 1970’s, and has required all cars sold in the state to conform to very rigid standards that are checked during the bi-annual smog check.  The smog test will determine whether or not your catalytic converter is cleaning the exhaust to the level that has been set for your year, make and model of vehicle.  If the test determines that your car or truck does meet those standards, then all is well and when all fees are paid, you are issued the smog certificate and can register your vehicle for use on the road.  If, however, your vehicle does not pass the smog test, then you will be required to have someone make an evaluation of the problems and correct them before you can re-test the vehicle. 

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Most people will automatically assume that the catalytic converter is the reason that the smog test has failed, and usually that is correct although there are other things that could affect the tailpipe emissions.  If the evaluation of your vehicle does indicate that the catalytic converter is at fault, then it should be determined why the converter is not working correctly.  Has the engine not been properly tuned?  Has the engine been using oil or coolant that could be contaminating the internals of the converter?  Is there any indication that the converter has been over heated or damaged from hitting something?   Is there a rattling sound coming from the converter area?  

 

The first step should be to have a qualified technician check the vehicle. The technician will perform various tests to diagnose why the converter has failed and then correct the problem before a new converter is installed and possibly damaged from the same reason.  If the car/truck is new enough, the onboard computer system (known as On Board Diagnostics level 2 or OBDII) may have turned on the Check Engine light which indicates that the OBDII tests have noted some problem and have set a code within the computer to alert you that a problem has occurred that will damage the car and possibly has already damaged the converter.   The technician can connect a hand held computer that will allow him to “read the codes” and identify what problems the on board tests have identified.  Once that is done and the problems corrected, if the tech has determined that the converter has been damaged, then is the time to look into replacing the converter.

 

In the state of California, there are strict requirements as to what parts can be used to replace defective catalytic converters.  Prior to the 1995 model year, it is most likely that there will be an aftermarket part that can replace the original catalytic converter, and because of the age of the vehicle, usually it is very difficult to find a new, original catalytic converter so that necessitates the use of an aftermarket part.  Each vehicle has a state approved part that is based on the model year, engine size and physical placement of the converter, so you cannot just buy the cheapest one you can find and have it installed because, at some point during the smog test, the smog technician is required to verify that any replacement parts are the correct part number for that application.

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After the 1995 model year, the availability of aftermarket converters for use in California has become even more strict and, again, there are guidelines that have to be followed to determine which parts can be used on what vehicle.  

 

All vehicles have at least one converter and most have more than one.  In a "V" style motor, (a v-6, v-8 or v-10) there will be at least one catalytic converter for each bank of the motor, and a lot of vehicles have a third or fourth catalytic down the line.  So if there is a failure with one of the electronic controls or a mechanical failure that harms the catalyst system, it can affect multiple parts and become very costly.  

 

The state of California has an on-line web site that identifies, for 1996 and newer, almost every make and type of car or truck used in the state and then lists the legal parts that can be used to replace the original catalytic converter: https://ssl.arb.ca.gov/AftermarketParts/catalysts

 

So, after it has been determined that the vehicle needs a new converter, the technician will determine whether there is a legal aftermarket part for the car/truck, if not, then the customer will need to contact the dealer for the correct part.

 

One strange fact of the aftermarket industry is: the state mandates that the aftermarket catalytic converters have a 5 year, 50,000 mile warranty. That’s as opposed to the Original Equipment replacement converters that have only a 1 year, 12,000 mile warranty.  

The aftermarket manufacturers make it very difficult to warranty a replacement converter.

 

If it becomes necessary to replace an aftermarket converter, the manufacturer will require all of the original paper work, sometimes asking for the original repair order for the work performed prior to installing the replacement converter.  They also want to see a copy of the smog test, pass/fail for both before and after repairs.  So it is very important to have a qualified shop look into what problems have caused the failure of the original or aftermarket converter.

 

There are several conditions that will void any warranty such as, signs of external damage from hitting something, indications of overheating, discoloration of the outside of the converter (which can indicate overheating), rattling of the internals, melting of the internals or excessive residue on the internal catalyst material which would indicate engine problems.  If there are no visible signs of failure and all of the paper work is available, then the part will be sent to the manufacturer who has the final word as to the warranty.  If the warranty is approved, then the part and labor cost will be reimbursed to the customer.  

 

If you reside here in Ventura County and need a qualified smog technician, we have several shops that we can recommend that can perform the necessary diagnostics and repairs, give us a call and we will be glad to talk with you about who and where we would suggest.

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Eric Griffin