Catalytic Converters: What They Do, What Goes Wrong And Much More…

Everyone has heard of a ‘cat’ or catalytic converter, but if you think about it, could you explain to someone what a catalytic converter actually does? Do you know what a catalytic converter looks like? And, more importantly, could you spot a catalytic converter’s signs of failure? Worry not, we’re here to talk you through everything, from how long a catalytic convert lasts to identifying potential problems and even how you go about using catalytic converter cleaners.

1 – What does a catalytic converter look like?

Here are a few examples. As you can see the design of catalytic converters varies quite a lot. Broadly speaking they look a little bit like a smaller exhaust silencer (muffler if you’re from the States), and are usually slimmer too, plus they’re nearly always closer to the engine. In fact, most cats these days are right up close to the engine so that they’ll warm up quicker, often integrated into the exhaust manifold itself as you can see in a few of the examples below.

Catalytic Converters: What They Do, What Goes Wrong And Much More

2 – What does a catalytic converter do?

The basic reason for a catalytic converter is to clean up the exhaust gasses from an engine (regardless of whether it’s fuelled by diesel, petrol, LPG or whatever) before they exit the exhaust pipe. The name refers to the chemical reaction that takes place inside and is started by a catalyst material – usually small amounts of a precious metal such as platinum, palladium or rhodium. The car makers aren’t doing this out of the goodness of their hearts though, as world governments set ever stricter limits on the emission of pollutants from vehicles. The current limits are impossible to achieve for an internal combustion engine without the use of a catalytic converter of some description – and a lot more technology and exhaust after-treatment besides.

Catalytic Converters: What They Do, What Goes Wrong And Much More

It should be noted here that we are talking about harmful pollutants, such as carbon monoxide (CO), oxides of nitrogen (referred to as NOx) and unburned hydrocarbons (HC), not soot and particulates, which are dealt with by a DPF in diesel cars. Also, don’t confuse these pollutants with the widely used ’emissions’ rating, which is based on carbon dioxide (CO2) output – that is not classed as a harmful substance and there are no legal limits on it in terms of individual vehicles.

No doubt you’ll know a petrolhead that knows a thing or two about cars and you may have heard them extol the virtues of removing the catalytic converter completely, making you wonder “how does catalytic converter affect performance?” They do, admittedly, restrict the exhaust a little, effectively reducing an engine’s potential power output, but their design and electronic engine control has come a long way, so they’re not as stifling as some will say. It’s never a good idea to tamper with the exhaust after-treatment in a car, as the gains will be small and come MOT or NCT time, if your cat is missing you’ll instantly fail.

3 – Why does a catalytic converter go bad?

You could also ask “how long will a catalytic converter last?” If an engine ran exactly like it was supposed to forever, then its catalytic converter would probably never go fail, but sadly, few cars remain perfect forever, do they? Put simply, a catalytic converter will fail when stuff that shouldn’t, goes into it. This can come from a variety of sources, such as a coolant or oil leak internally in the engine, or even using certain engine cleaning or anti-wear additives (though most modern additives are compatible with catalytic converters). Even using the wrong oil for the car can cause deposits on the surface of the catalytic converter that prevent it from working properly. Likewise, if a car is misfiring for any reason (in petrol cars, this could be caused by ignition or fuel supply system issues) a lot of unburned fuel could end up inside the catalytic converter, rendering it useless. In extreme situations, or if the problem goes undiagnosed, the core of the catalytic converter, called the substrate, can physically break down and cause a blockage in the exhaust. This leads to a catalytic converter loss of power and is a clear sign of failure, as is a drastic increase in average fuel consumption. Some of these symptoms may occur when a catalytic converter becomes clogged up with carbon deposits too, which happens very gradually over time.

What happens when a catalytic converter stops working

4 – What happens when a catalytic converter stops working?

If the substrate is intact, but the surface of the catalytic converter has become contaminated, then it may not be obvious to the driver that there is anything amiss. The emissions from the exhaust might smell different and the car will emit more pollutants, but there may be no obvious symptoms from the drivers seat. If you’re ever following another car and get a really strong sulfurous smell, it’s more than likely their catalytic converter is on the blink. Most modern cars, however, have on-board diagnostics that use oxygen sensors before and after the catalytic converter to detect when anything changes that might affect what’s coming out of the exhaust; and hence an engine check light will illuminate permanently in the dashboard if the converter is not working correctly. At which stage it’s time to hook the car up to a diagnostics computer to confirm what the problem is. It’s also possible that a car’s ECU will switch into ‘limp home’ mode until the issue is rectified, with severe loss of performance.

Catalytic Converters: warning light

5 – How does catalytic converter cleaner work?

There are different products on the market, but generally you pour the liquid into a full tank of fuel and drive as normal. The catalytic converter cleaner then works to break down carbon deposits, not just in the catalytic converter itself, but throughout the whole fuel system. This should help increase the efficiency of the converter, assuming that it has no physical damage or that the substrate is intact. It may be that it will take several applications of catalytic converter cleaner, depending on how old or clogged up it is and it may also be necessary to reset the car’s ECU to clear any relevant fault codes.

6 – How much do catalytic converts cost?

This is a bit of a ‘How long is a piece of string’ type of question as the price varies wildly depending on the car, engine and type of cat. The cheapest catalytic converter we stock at is about €/£60 but prices can go up to the thousands depending on the complexity of the design. Cats that are an integral part of the exhaust manifold tend to be a lot more expensive, especially if fitted to a multi-cylinder V6 or V8 engine for example – in some cases, there may even be 2 catalytic converters on cars with two banks of cylinders.

where to buy Catalytic Converters