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 honey-comb matrix coated with precious metals through which the exhaust flows. Its main job is to react with and remove harmful gases from the exhaust stream to improve the vehicle’s emissions.
Laws in the UK vary from region to region. But generally, it is required that a vehicle have a functional catalytic converter for it to be sold or operated. Exceptions are made for older vehicles that were designed and sold without catalytic converters originally.
The 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.
To be able to differentiate the prices based on these factors, below are some estimates of the catalytic converter replacement costs for some common vehicles, taking £70 an hour as a labour rate:
- For a 2005 Honda CR-V with a 2.4-liter engine, the labour time is estimated at around 0.6 of an hour. A factory part costs about £2,550, a certified replacement costs about £284, and a non-certified replacement costs about £175. The total cost to complete the job would be about £2,590 using OE parts, about £326 using a certified aftermarket part, or about £217 using a non-certified part.
- For a 2007 Jeep Wrangler with a 3.8-liter engine, the labour time is estimated at around 1.8 hours. A factory replacement part costs about £855, an OE-compliant part costs about £808, and an uncertified part costs about £396. The total cost to complete the job would be about £980 using OE parts, about £935 using certified aftermarket parts, or about £520 using uncertified parts.
- For a 2006 Chevrolet 1500 four-wheel-drive truck with a 5.3-liter engine, the labour time is estimated at around 1.4 hours. A factory replacement assembly costs around £400, an OE-certified part costs about £430, and a non-certified part costs about £300. The total cost to complete the job would be about £500 using factory parts, about £530 using certified aftermarket parts, and about £400 using non-certified parts.
- For a 2005 Nissan Maxima with a 3.5-liter transverse V-6 engine, there is a front and a rear catalytic converter, replaceable separately. The labour time to replace the front catalytic converter is 1 hour, the factory catalytic converter price is about £650, and a compliant non-OEM part costs about £225. The total cost to complete the job for the front would be about £720 using factory parts and about £295 using certified aftermarket parts. For this vehicle, the labour time to replace the rear catalytic converter is estimated at 3.4 hours. A factory replacement part costs about £640, and a compliant non-OEM part costs about £220. The total cost to complete the job for the rear would be around £880 using factory parts and about £460 using certified aftermarket parts.
In all cases, there is the likelihood of some relatively small additional costs for gaskets and hardware.
It is also quite common to replace the O2 sensors with the catalytic converter. Ordinarily, they can be removed from the old part and installed into the new part (the labour being included in the job cost).
However, heat issues can cause them to seize up or have 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 is concerned, 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 converter 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.
But unfortunately, this leads to a common issue. While an OEM replacement catalytic converter will have the same capacity as the original and satisfy the expectations of the PCM, not all aftermarket converters are tested for capacity.
The expensive part of a catalytic converter is the catalyst itself, which incorporates precious metals into a matrix. Economising on this surely saves costs, but, in the bargain, decreases capacity.
It is then possible to buy and install a new converter, and after a short time, have the same fault code come back that ultimately leads to a part replacement. The most likely case is that the converter doesn’t meet the capacity requirements for the vehicle.
The best way to be safe is to either choose an OEM replacement catalytic converter or an aftermarket compliant converter. This means that it has been tested and meets the strict UK emissions requirement that a replacement converter has at least the capacity of the original part.
In several regions, this is a mandatory requirement. However, it varies from region to region (and even year to year as well). On the simple guiding principle that it’s best to avoid having to do an expensive job twice, going with either an OEM-compliant or an actual OEM catalytic converter is the most 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 the 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 very sure of the part warranty if either of these is done. However, 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 when it can be done legally.
Catalytic Converter Replacement
In most cases, an engine light will be the only indication of catalytic converter failure; the codes P0420 and P0430 are the common ones. The general rule for diagnosis is to repair any other engine fault codes first, rule out exhaust leaks, verify if the converter fault is persistent, and then, finally, replace the catalytic converter.
Most of the time, the catalytic converter is a bolt-on part and not too hard to access. Replacement can still be a bit difficult 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 – through an expensive OEM arrangement.
In any case, if one catalytic converter has failed due to age or operating conditions, the other would most likely be in the same shape.
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 an extremely 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 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 result 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 catalysing 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 down and obstruct the exhaust flow. If a catalytic converter needs to be replaced due to overheating, it’s always 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 if oil changes have been neglected for a long time, allowing thickened oil to gum up the free movement of the rings, then more oil will be left on the cylinder walls than designed.
Older and neglected engines tend to burn more oil, and that can cause problems with the catalytic converter. This typically leaves carbon deposits on the active matrix that interfere with its 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 the realistic long-term solution can be more complicated than just 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 this 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.