You are probably reading this page because you have been advised that your vehicle needs a catalytic convertor. You may have been advised how much it will cost and were taken back to say the least by how much the quote was. You may even have looked online and found a part that looks similar for a much less expensive price. Now you wonder why the huge discrepancy in price. I will attempt to explain this very technical process and why prices vary so greatly.
WHY DOES MY CAR NEED THE CATALYTIC CONVERTOR
Catalysts are needed to reduce emissions to acceptable levels without dramatically reducing performance and fuel economy. This is true of HC, CO and NOx, but NOx is the emission that is most dependent on the catalyst for emissions compliance.
NOT AS EASY AS IT SOUNDS (Boring Scientific Part Alert)
For modern Catalytic Convertors to effectively reduce emissions for clean air very complex chemical reactions must take place. One reaction cleans some emissions but not other harmful emissions. For the remainder of the emissions to be cleaned a different chemical reaction must take place within the convertor.
There are actually two types of catalysts. Reduction catalysts cause NOx to be reduced into O2 and N2. Oxidation catalysts cause HC and CO to oxidize with any available oxygen into CO2 + H2O. Unfortunately, oxidation will only occur when there is enough free oxygen, and reduction will only occur in a relative absence of free oxygen. Rhodium is generally the most efficient reduction catalyst. Platinum and palladium are used for oxidation. 2-way catalytic converters are oxidation catalysts. They oxidize CO and HC but do not reduce NOx. 3-way catalysts oxidize and reduce. They oxidize CO & HC and reduce NOx. Proper air /fuel mixture control and exhaust oxygen content is required for proper 3-way catalyst performance. In general, oxidation and reduction can not both occur at their highest efficiency at the same time.
Reduction efficiency is not at it’s highest unless the oxygen content is very low. This usually doesn’t happen unless the air/fuel mixture is at least a little bit rich. Oxidation only reaches it’s highest efficiency when the oxygen content is fairly high. That happens when the mixture is at least slightly lean.
To further complicate matters. Many cars do not have air injection. Without air injection and a slightly rich mixture these cars must depend on something else to manage the oxygen in the catalytic converter. Cerium is an element that attracts oxygen. Under high oxygen conditions the cerium will absorb oxygen and allow NOx reduction to occur with greater efficiency. Under low oxygen conditions the cerium will release it’s stored oxygen to increase the oxidation efficiency of CO and HC. Cerium is very important in any 3-way catalyst. Even dual bed catalysts benefit from cerium. The cerium can allow the front bed of a dual bed catalyst to continue reducing NOx at close to maximum efficiency without a rich mixture.
WHY SO EXPENSIVE
In the previous section we mentioned precious metals. They are Platinum, palladium, cerium, and Rhodium. These elements are extremely expensive and I have included a ticker below to show that they are nearly the price of gold if not higher.
To create an effective catalytic convertor (one that is effective at cleaning the exhaust emissions and that will last a long time) the manufacturer must use these elements in the correct proportions. Problem is, there is no way for most of us to test for these elements, or even know the correct proportions. There is however absolutely no doubt that many of the less expensive options do not perform correctly. We know this because after they are installed the emissions test no better and in some cases worse!
WHO IS THE MOST LIKELY TO USE THE CORRECT ELEMENTS IN THE PROPER PROPORTIONS?
The companies most likely to use the correct proportions of precious metals to manufacture their catalytic convertors is the Original Equipment Car Manufacturer. Why? Because they stand the most to lose if the convertor doesn’t
- Meet expectations for cleaning emissions. They face heavy fines from the EPA if their vehicles do not meet standards for clean air.
- Last a long time. The government forces them to warranty them for at least 5 years 50,000 miles and sometimes longer. They must replace them if they fail to perform.
ARE THERE ANY OPTIONS.
Yes and No.
There is only one know certifying body that we know of that tests the effectiveness of catalytic convertors in the sold in the United States. That government organization is the California Air Resources Board (CARB). They do extensive testing to check the effectiveness of the convertors voluntarily presented to them for testing. This is optional for companies that manufacture convertors. If this organization has tested the convertor and it passes minimum efficiency standard they will authorize the company to clearly stamp CARB on the convertor body itself.
While not all vehicles have a CARB certified convertor available we can check and see if there is one for yours.
CLEAN AIR IS A RESPONSIBILITY.
Bottom line if you purchase and install a convertor that is not either OE original equipment or CARB certified you run a very high risk of not effectively cleaning the air emissions from your vehicle. Even if you do install a CARB certified convertor there is no assurance that it will clean your cars emissions long term.
Clean air is important for all of us and doing our part sometimes results in expensive repairs to our vehicles. For the good of all we at Advanced Auto Pros recommend using OE catalytic convertors. While we will at times install a CARB certified convertor we warn our clients to be aware we cannot guarantee the part will perform the same or last as long.