Can a catalytic converter unclog itself?

(Last Updated On: April 11, 2023)

It’s likely that being clogged is the reason for a faulty catalytic converter, but can a catalytic converter unclog itself and what can you do to prevent this from happening again.

A catalytic converter is a part of the exhaust system, which is internally shaped like a honeycomb; the holes in the honeycomb allow exhaust gases to pass through. The honeycomb catalyst is made from precious metals such as platinum, palladium, and rhodium. The pollutants in exhaust gases pass through the catalyst, which is converted into water and carbon monoxide by catalyzing a redox reaction. The honeycomb airways can get clogged for several reasons, which we will go through in this article. A catalytic converter is a relatively expensive exhaust piece, so it would be better if it could self-repair and unclog itself, right?

Can a catalytic converter unclog itself?

Yes, a catalytic converter can unclog itself. A catalytic converter goes through a similar process to a DPF regeneration at operating temperatures. When the catalytic converter is hot enough, it cleans and unclogs blockages. So, driving at a higher revolution per minute, such as 4000 – 6000 RPM in a lower gear on a fast road for 30 minutes, should rectify any blockages. This will heat the catalytic converter and ensure it stays as hot as possible when driving.

Driving economically at lower RPM the catalytic converter will get hot, but a much longer journey will be needed for it to self-clean. Expect the car to stutter as you drive along, this is just the blockages clearing under heavy engine load.

However, be aware that if the catalytic converter is too far gone, driving will probably not clear a clogged catalytic converter, and a replacement or removal for cleaning be the only fix.

How to tell your catalytic converter is clogged

To tell if a catalytic converter is clogged is relatively straightforward; just by checking the amount of exhaust gases exiting the car’s exhaust, you may be able to tell if there is a blockage. There are some other signs that a blockage is starting to form or already has:

  • Reduced Engine power Reduced engine power is a good indicator the catalytic converter is clogged. If a catalytic converter is blocked, pressure forces waste exhaust gasses back into the engine, reducing the amount of clean air being sucked into the cylinder during the next burn cycle, and reducing the engine performance.
  • Poor fuel efficiency – Not always the easiest to tell, but if you notice a drastic reduction in the fuel efficiency of your vehicle is a good indication of an issue. Sensors pick up an imbalance in the exhaust gasses, which will tell the vehicle to add unnecessary fuel, running too rich. It can also cause the car to run too lean, as you guessed; this will cause the exact opposite and give you a reduction in engine performance.
  • Trouble starting the engine – Once clogged and then trying to restart the engine, the car will have a similar effect as driving with reduced engine power.
  • Smell of Rotten eggs – The eggy smell comes from the sulfur found in fuel; the catalytic converter usually filters this, so it’s odorless, but when it clogs, it can no longer filter the exhaust gasses and unburnt fuel. So, the smell becomes apparent.
  • EML on – Either side of the catalytic converter is electrical sensors connected to the car ECU (the brain of the car) called Lambda sensors (AKA O2 sensors); if the car catalytic converter becomes clogged, the sensors will pick up an issue in the gasses flowing through the exhaust and can signal engine management light to illuminate on the dashboard. A faulty Lambda sensor can signal the EML light to come on.
  • Engine misfire – An engine misfire can be caused by a clogged catalytic converter, which you can read more about here.
  • Discoloured catalytic converter – A blocked catalytic converter will be overheating, turning the metal casing purple. Overheating is the result of unburnt fuel igniting in the catalyst.

Can a catalytic converter be unclogged?

A partially clogged catalytic converter can sometimes unclog itself by using a fuel additive and taking the car for a long drive on a fast road. The car must get to operating temperatures and consistently stay there for the catalytic converter to get extremely hot and carry out its ‘self-cleaning’ function of burning off the hydrocarbon blockage. You should note this can’t be carried out on a severe blockage.

You can also manually unclog the catalytic converter by removing it and cleaning the blockage; however, not everyone should carry this out. It’s pretty easy to damage the honeycomb catalyst of precious metals inside the catalytic converter if you don’t know what you are doing. There are services where they will remove the catalytic converter and clean it for you; again, this depends on how nasty the clog is and the cause of it. It’s not a very common service as the labor and time involved in inspecting can mean it’s cheaper to replace rather than repair.

Why does a catalytic converter become clogged?

A catalytic converter can become clogged for a number of reasons,

  • Engine misfire – The most common is a misfire developing in the engine caused by faulty spark plugs or ignition leads. As the fuel is not being burnt correctly, the unburnt fuel is forced into the exhaust system, and the heat inside the catalytic converter will ignite the unburnt fuel causing the honeycomb structure to melt and clog.
  • Faulty O2 sensors – Oxygen sensors detect the level of oxygen in the exhaust gasses. The ECU passes this information to adjust the air-to-fuel ratio injected into the engine. When one of the sensors becomes faulty, the incorrect or no reading signal is sent back, asking for extra fuel or taking some out of the next burn cycle, which will cause a blockage.
  • Overfilled engine oilA car overfilled with engine oil can force oil into the exhaust system, creating a carbon and soot build-up in the catalytic converter. An excess amount of soot and carbon deposits will block the exhaust flowing through the pores of the catalytic converter.
  • Constant short journeys – driving constant short journeys means the catalytic converter never reaches operating temperatures where it can burn away hydrocarbons. A considerable number of hydrocarbons will start to clog the catalytic converter, although this is relatively easy to clear.

Tips for taking care of a catalytic converter

Like almost all mechanical components in a vehicle, the best way to take care of them is to drive the car. A catalytic converter will take around 15 minutes of driving to get up to operating temperature and then about 15 – 20 mins to burn the build-up of hydrocarbons stored. Driving for 30 minutes weekly is enough to allow the catalytic converter to do its job.

Also, engine fuel additives can be used and poured into the fuel tank, which specializes in helping to clean the catalytic converter. Although these can’t be used every time you fill up a vehicle, they work as a good ‘mini service’ to the catalytic converter every so often.

Can driving at high speeds for a prolonged period of time unclog a catalytic converter?

Driving at high speeds for a prolonged period may temporarily improve the performance of a clogged catalytic converter, but it is unlikely to unclog it completely. A clogged catalytic converter is caused by a buildup of debris and pollutants within the catalyst, which restricts exhaust gas flow and reduces its ability to process them.

While driving at high speeds may cause the buildup to shift or break apart slightly, it is unlikely to clear the blockage fully. Driving at high speeds may cause further damage to the catalytic converter or other parts of the exhaust system.

To Summarise

A catalytic converter can become clogged for several reasons, but almost every time, it will be a supporting component or engine part that has failed. A clogged catalytic convert can unclog itself if it is a minor blockage caused by a build-up of hydrocarbons. It’s also possible to remove a catalytic converter and clean a blockage, but some blockages caused by unburnt fuel such as a melted catalyst cannot be cleaned and will require replacement. If you sense your vehicle has changed the performance or fuel efficiency, consider the catalytic converter might be the cause and have your car inspected by a mechanic.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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