The catalytic converter is a part of the exhaust system that is located after the exhaust manifold and before the muffler. The active part of a catalytic converter is a honeycomb matrix coated with precious metals (usually platinum, palladium, and rhodium) through which the exhaust flows. Its main job is to react with and convert harmful gases in the exhaust stream to improve the vehicle’s emissions.
Laws vary from state to state, and sometimes across different regions within a state. But usually, it is required that a vehicle have a functional catalytic converter in order to be sold or operated. Exceptions are for older vehicles that were originally designed and sold without catalytic converters.
Most of the time, the catalytic converter is a bolt-on part that is not too hard to access. Replacement can still be problematic due to the high temperatures it runs at.
Exhaust-specific fasteners are usually used, which manage heat well but are more prone to rust. It’s very common to replace the fastening bolts and hardware along with the catalytic converter. It’s also very common to have the old parts break, shear off, have to be removed with a torch or cutting tool, etc.
On a V-6 or V-8 engine, there is usually one catalytic converter for each bank of cylinders, and these are often not replaceable separately. A pre-formed Y-pipe with two catalytic converters is more common.
In any case, if one catalytic converter has failed due to age or operating conditions, the other is likely in the same shape.
Cost of Catalytic Converter Replacement
The cost of vehicle repairs or parts replacement is dependent on several factors such as the type and model of the vehicle, the type, and quality of the parts to be used, as well as the location of the auto shop doing the service.
Below are some estimates of the catalytic converter replacement costs for some common vehicles using $150 an hour as a labor rate:
- For a 2005 Honda CR-V with a 2.4-liter engine, the labor time is estimated at around 0.6 of an hour. A factory-listed Walker replacement costs about $2782, a CARB-compliant Walker replacement costs about $820, and a non-certified Davico replacement costs about $510. The total cost to complete the job would be about $2872 using OE parts, about $910 using a certified aftermarket part, or about $600 using a non-certified part.
- For a 2007 Jeep Wrangler with a 3.8-liter engine, the labor time is estimated at around 1.8 hours. A factory replacement part costs about $4,845, an AP CARB compliant part costs about $1,280, and an uncertified Ultrapower part costs about $780. The total cost to complete the job would be about $5,115 using OE parts, about $1,550 using certified aftermarket parts, or about $1050 using uncertified parts.
- For a 2005 Nissan Maxima with a 3.5-liter transverse V-6 engine, there are two front and one rear catalytic converter, replaceable separately. The labor time to replace a front catalytic converter is 1 hour, a factory catalytic converter price is about $1240, and a Walker CARB compliant part costs about $900. The total cost to complete the job for the front would be about $1390 using factory parts and about $1050 using certified aftermarket parts. For this vehicle, the labor time to replace the rear catalytic converter is estimated at 3.4 hours. A factory replacement part costs about $1130, and a Walker CARB compliant part costs about $940. The total cost to complete the job for the rear would be about $1,655 using factory parts, or about $1465 using certified aftermarket parts.
In all cases, there is the likelihood of some relatively small additional costs for gaskets and hardware, especially related to rust, for exhaust systems.
It is also fairly common to replace the O2 sensors with the catalytic converter, and ordinarily they can be removed from the old part and installed in the new part (the labor being included in the job cost).
However, heat or rust issues can cause them to seize up or lead to damaged threads, and sometimes, if a catalytic converter is being replaced for contamination issues, it’s prudent to assume that the O2 sensor may also be affected.
Aftermarket Versus Original Equipment
As far as doing the job it is designed to do, one of the most important things about a replacement catalytic converter is something you can’t see or directly test: its oxygen capacity. This determines how effectively the cat can act on the vehicle’s exhaust stream.
A vehicle with a large displacement engine moves more air and requires a larger capacity catalytic converter, while the reverse is true for a smaller engine. The engine’s computer uses the oxygen sensor data to monitor the oxygen capacity of the catalytic converter.
This, then, leads to an unfortunately common issue. While an OE replacement catalytic converter will have the same capacity as the original and satisfy the expectations of the PCM, not all aftermarket cats are tested for capacity.
The most expensive part of a catalytic converter is the catalyst itself, which incorporates precious metals in a matrix. Economizing on this saves costs, but decreases capacity.
It is then possible to buy and install a new cat and, after a short time, have the same fault code come back that led to the replacement. Usually, that code is P0420. The most likely case is that the cat doesn’t meet the capacity requirements for the vehicle.
The best way to be safe is to either choose an OE catalytic converter or an aftermarket CARB compliant converter. This means that it has been tested and meets the strict California emissions requirement that a replacement converter have at least the capacity of the original part.
It is then possible to buy and install a new cat and, after a short time, have the same fault code come back that led to the replacement. The most likely case is that the cat doesn’t meet the capacity requirements for the vehicle.
The best way to be safe is to either choose an OE catalytic converter or an aftermarket CARB compliant converter. This means that it has been tested and meets the strict California emissions requirement that a replacement converter have at least the capacity of the original part.
In several states, this is a requirement. However, it varies from state to state (and year to year as well). On the general principle that it’s best to avoid having to do an expensive job twice, going with either a CARB-compliant or an OE catalytic converter is the prudent choice.
In several states, this is a requirement. However, it varies from state to state (and year to year as well). On the general principle that it’s best to avoid having to do an expensive job twice, going with either a CARB-compliant or an OE catalytic converter is the prudent choice.
The least expensive way to replace a catalytic converter is to install a “universal” replacement part, which is usually made to be welded into place of the original, or a slightly more expensive non-certified part.
Universal catalytic converters are generally only installed at muffler shops that have the proper pipe-forming and welding equipment. Non-certified parts are usually bolt-on replacements that most shops could install.
It’s best to be sure of the warranty if either of these are done. Though if the part works without issue for the first month or two, that usually means it will be fine for the long term.
While they can cause issues, the cost savings are usually significant where they can legally be done.
Symptoms of a Failed Catalytic Converter
In most cases, an engine light will be the only indication of catalytic converter failure, with the codes P0420 and P0430 being the most common ones. The general rule for diagnosing that code is to repair any other engine fault codes first, rule out exhaust leaks, verify if the converter fault is persistent, and then replace the catalytic converter.
Another symptom can be a “rotten eggs” smell from untreated hydrogen sulfides in the exhaust stream. Ordinarily, the catalytic converter would take care of those.
Rattling noises are also possible, though rattling noises in the exhaust are more often caused by loose heat shields or exhaust mounts. But if the catalytic converter overheats, melts, and fractures, there can be chunks of the core floating around inside the housing, which can make rattling noises. That can also cause persistent or intermittent engine running problems, if the loose chunks fall in a way that blocks the exhaust stream.
What a Catalytic Converter Does
Most modern catalytic converters can also be called “three-way” converters. This means that they accomplish three different specific operations on the exhaust stream.
The first is that they strip the oxygen molecule from nitrogen oxides. Nitrogen oxide is a product of the burning of hydrocarbons and is the main ingredient of the brown, hazy smog,” a lung and eye irritant. The byproducts of this are harmless nitrogen and a free oxygen molecule.
The second operation is to add an oxygen molecule to carbon monoxide, which is another very harmful product of burning hydrocarbons. Carbon monoxide is a particularly deadly gas, but adding a molecule of oxygen to it creates carbon dioxide.
This has problems in itself, of course (being the infamous CO2), but it is more inert and not immediately harmful in low concentrations. The third operation also consumes free oxygen to convert unburned hydrocarbons into CO2 and H2O.
The main way that the PCM determines the efficiency of a catalytic converter is by looking at data from the O2 sensors before and after the catalytic converter and using that data to infer the oxygen capacity of the converter. This is more or less its capacity to perform the last two operations.
Problems that Can Lead to Catalytic Converter Failure
The conversion of unburned hydrocarbons in the exhaust stream is an essential role of the catalytic converter. However, it can also lead to problems if they are excessive, as the process itself generates heat.
Hydrocarbons in the exhaust stream can normally come from hard acceleration or less than perfect combustion. They can also form from various engine problems (both mechanical and sensor-related) leading to a too-rich fuel mixture, poor combustion, or engine misfires.
In small amounts or for brief periods, usually no harm is done. Nevertheless, the catalyzing of hydrocarbons creates heat, and it is possible for the catalytic converter to overheat if it’s exposed to too much-unburned fuel.
In the worst cases, the core can melt and obstruct the exhaust flow. If a catalytic converter needs to be replaced due to overheating, it’s always a good practice to diagnose and repair any running issues it has at the same time.
Oil burning can also cause issues. Every engine burns a little bit of oil by design, as oil lubricates the cylinder walls as the rings move against them to prevent wear. As the rings age and especially if oil changes are neglected, thickened oil can gum up the free movement of the rings. However, more oil can be left on the cylinder walls than designed.
Older and neglected engines tend to burn more oil, which can cause problems with the catalytic converter. This typically leaves carbon deposits on the active matrix that interfere with the effective operation.
This can lead to a check engine light for inadequate catalytic converter efficiency. If an oil consumption problem leads to a failed catalytic converter, then, a realistic long-term solution can be more involved than simply replacing the catalytic converter.
Coolant in the exhaust stream can also damage a catalytic converter by creating a barrier coating of contaminants on the surfaces of the matrix that prevents its operation in the same way that an oil consumption problem can cause a problem.
This coolant would usually only come from a head gasket fault, and it can leak very slowly over a long period of time. One of the things that should be ruled out or looked at when replacing a failed catalytic converter is whether the engine has a problem with coolant loss, which might need to be diagnosed.
FAQs
- How long should a catalytic converter last?
They are designed to last the life of the vehicle.
- What causes catalytic converters to fail?
Poor engine running conditions, oil consumption problems, misfire problems, and any contaminants (oil, coolant, unburned fuel, etc.) that wind up in the exhaust stream.
- Can a catalytic converter be cleaned?
Generally not. There are products available for it, but in most cases, they don’t result in a working catalytic converter.
- Can I replace my own catalytic converter?
Maybe, but it is often a challenge. Rust can be a big complication, as can seized or broken bolts. Cutting tools and welding tools are basic equipment.
- If I have a P0420 or P0430 code, could that be an O2 sensor?
In theory, yes, but generally, the PCM monitors O2 sensor operation pretty closely. If an O2 sensor needs replaced, there are many other codes that would be more likely. Replacing the O2 sensors is a relatively inexpensive thing to try, but it is unlikely to fix the problem.
- If I reset the code, how long should it take to come back if it’s not fixed?
Usually within a couple hundred miles.
- Can I drive with a bad catalytic converter?
As long as the core hasn’t melted down and blocked the exhaust stream, yes. The engine should work fine; the only symptoms are the engine light on and poor emissions. Which, of course, in most areas may prevent the vehicle from being registered.
- What is the best way to prevent catalytic converter failure?
The main thing is to maintain the engine. A well-maintained engine shouldn’t consume oil, and a good-running engine will have only minimal unburned hydrocarbons in the exhaust stream.