Do Diesel Engines Have Catalytic Converters?

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toxic gases

With pollution levels rising at an accelerated rate, governments have implemented strict regulations on environmental pollution, the bulk of it caused by automobiles.

To help reduce the emission of toxic fumes like carbon monoxide, hydrocarbons, and nitrogen, car manufacturers install a catalytic converter in the exhaust system of vehicles.

If you drive a diesel vehicle, you’re probably wondering if diesel cars have a catalytic converter and how it works. So, let’s dive in!

Do diesel cars have catalytic converters?

Yes, diesel cars have catalytic converters but they work differently than in cars with gasoline engines. Diesel and gas engines are significantly different. In internal combustion engines (gas engines), a spark is used to ignite the fuel in a gasoline-powered vehicle. In contrast, a diesel engine uses compression to light the fuel. Because of the high air-to-fuel ratio required, this approach requires a high amount of oxygen to complete the ignition.

So, how does a diesel catalytic converter work?

diesel catalytic converter

The diesel catalytic converter is more than just a pollution filter for your car. It also functions as a rearranger. By rearranging the atoms, the catalytic converter transforms the chemical components of exhaust fumes.

The majority of the process is completed in four phases.

  • EGR (exhaust gas recirculation)
  • DPF (diesel particulate filter)
  • DOC (diesel oxidation catalyst), and
  • SCR (selective catalytic reduction)

Diesel Oxidation Catalyst (DOC)

A Diesel Oxidation Catalyst is a component of every diesel system. It’s generally the first component in the exhaust system.

It transforms carbon monoxide into carbon dioxide and decomposes any un-spent fuel. In terms of functionality, this portion of the diesel catalyst system works similarly to a gas catalytic converter.

The DOC is usually the smallest element of a diesel converter, but it’s also the most valuable one since much of the platinum and palladium are found in this region, giving it a high recycle price tag.

Diesel Particulate Filter (DPF)

diesel particulate filter

Diesel engines create a second polluting by-product that an internal combustion engine doesn’t. They are typically referred to as particulates or soot. The DPF uses a wall-flow monolith with alternating open/closed channels to capture these particles from the inlet side and keep them trapped until they can be broken down and removed by a process called “regeneration”.

The regeneration process is similar to the oxidation procedure in the DOC, which involves burning organic material to generate CO2 and water.

The DPF is equipped with tiny amounts of platinum and palladium to aid in the catalysis process. The soot must also be heated to a high temperature, which will allow it to burn up and pass through the filter walls and out the tailpipe. Normally, the vehicle’s onboard computer governs regeneration.

Selective Catalytic Reduction (SCR)

This component is responsible for reducing NOx gases. Rhodium is the rare metal that promotes the reduction process in a three-way converter, converting nitrogen oxides to their individual molecules, nitrogen, and oxygen. However, because diesel exhaust has a high level of oxygen, rhodium cannot effectively reduce NOx in a diesel converter. As a result, diesel converters generally do not contain rhodium.

Instead, the SCR employs a chemical known as “diesel exhaust fluid” (DEF), which is composed of either ammonia or urea. The ceramic monolith still includes catalytic materials, although these are generally non-recyclable. The NOx can be effectively eliminated from the exhaust by utilizing the DEF and catalysts.

A small portion of platinum may be found in some SCR catalysts known as the “ammonia slip catalyst,” which is housed near the rear of the biscuit. Its goal is to eliminate any extra ammonia from the system. The amount of platinum on this section is usually so little that it isn’t worth recycling.

Another approach to decrease NOx in a diesel engine is exhaust gas recirculation (EGR). This technique does not require an SCR catalyst or DEF, so not all diesel vehicles will have one.

How long do diesel catalytic converters last?

A diesel catalytic converter, on average, lasts 10 years or 100 000 miles. However, this will also be influenced by the duration and number of stops the vehicle makes. The catalytic converter will wear out faster in a car that makes brief start-stop journeys than one that travels long distances continuously.

Because the engine is turned off before the catalytic converter reaches its optimal temperature range, it does not fully catalyze reactions. Despite their longevity, catalytic converters must be inspected on a regular basis for external and internal damage. It’s expensive to replace one that has been damaged.

What are the signs of a bad catalytic converter?

Catalytic converters can fail due to a variety of reasons, including carbon deposits build-up, restricting the exhaust gases’ free flow. Overheating, physical damage, and infection are other possibilities.

The specific symptoms will depend on what type of converter your vehicle is equipped with, but you might see any of the following:

  • acceleration issues
  • poor engine performance
  • dark smoke spewing from the exhaust
  • the smell of rotten eggs from the exhaust
  • vehicle overheating

Modern automobiles have oxygen sensors that light up red if the converter isn’t working correctly. If you experience any of these indications, it’s time for a mechanical checkup.

Recycling diesel catalytic converters

Diesel engines may be found in a wide range of forms, from personal vehicles to commercial vehicles to heavy machinery to industrial applications. When purchasing diesel converters, there is a lot of variety in terms of size, design, and precious metal content to consider. The size of a biscuit can be deceptive; it’s not always simple to tell which component is valuable.

How much is a diesel catalytic converter worth?

Diesel catalytic converters are in demand all over the world, and their cost is a crucial aspect to consider. Despite the fact that the price varies according with the type and quality, you must choose. The global market for diesel catalytic converters is quite large.

Here are some average prices for different catalytic converters:

  • Small foreign catalytic converter: $108 – $141
  • Medium foreign catalytic converter: $121- $203
  • Large foreign catalytic converter: $202- $392
  • XL foreign catalytic converter: $398- $454
  • Foreign pre catalytic converter: $48- $71
  • Exotic catalytic converter: $225 – $450
  • High grade domestic catalytic converter: $145- $192
  • Pre- domestic catalytic converter: $27- $62
  • Torpedo catalytic converter: $80 – $250
  • Small catalytic converter: $83 – $158
  • Large catalytic converter: $154- $260
  • Large bread loaf catalytic converter: $138- $392
  • Small bread loaf catalytic converter: $104- $229
  • The foreign lite catalytic converter: $48- $75
  • Large Chrysler catalytic converter: $101- $189
  • The regular domestic catalytic converter: $68 – $104
  • Bread catalytic converter: $14 – $124
  • Diesel catalytic converter: $12- $124
  • Small foil catalytic converter: $12 – $ 32
  • Large foil catalytic converter: $29 – $64
  • Foil catalytic converter: $6 – $23
  • Half cat catalytic converter: Varies on different factors.
  • Aftermarket catalytic converter: $10
  • DPF catalytic converter: $9- $479
  • AC catalytic converter: $46 – $222


Catalytic converters are an essential component of diesel-powered vehicles. The platinum content in these devices is what enables them to clean up NOx emissions by converting them into less harmful molecules through a chemical reaction with oxygen and the help of other chemicals, such as urea or DEF. You can find catalytic converters on cars, trucks, buses, trains, ships – even large machinery like bulldozers! Catalytic converters may last 10 years; however, this lifespan will depend on how often you drive your vehicle (longer if you take more trips) and how well the device was manufactured (less time for high-quality products). If your car’s catalytic converter starts making noise or smells bad that might be indicative that it needs repair.

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