Teorio
Catalytic converter and exhaust emissions
This text explains how the catalytic converter in passenger cars works and why it is important for exhaust purification. You will learn what can damage or poison the catalytic converter and how this affects emissions and road safety in Sweden.
Rules & Regulations
- The catalytic converter and other exhaust-cleaning components must not be removed or tampered with in a way that worsens the vehicle's emissions; such changes can cause the vehicle to fail inspection and become illegal to use on the road.
- Faults in the exhaust cleaning system, for example a failing catalytic converter or a broken lambda sensor, must be repaired; driving with obvious exhaust faults can lead to increased emissions and remarks during checks.
- During service and repair, spare parts and fuels must be appropriate for the vehicle; incorrect fuels or unsuitable additives that poison the catalytic converter must not be used.
- Exhaust-related modifications to the vehicle (e.g. performance changes that affect emissions) usually require approval or re-inspection during technical inspection.
- Engine warning lamps related to exhaust cleaning (e.g. the malfunction indicator lamp) signal that the exhaust system may be malfunctioning and should be checked by a workshop.
Tips for Drivers
- Address ignition problems immediately: uneven combustion (misfire) or a rich fuel mixture can overheat and melt the catalytic converter.
- Do not drive for long with the engine warning light on — it can lead to serious damage to the catalytic converter and expensive repairs.
- Avoid using fuels or additives that are not recommended by the vehicle manufacturer, especially products that contain lead, silicone, or large amounts of oil.
- When towing heavy loads or after short journeys in cold weather, pay attention to changed engine performance; prolonged overload can damage the exhaust system.
Common Mistakes
- Believing that the catalytic converter 'removes everything' — it reduces carbon monoxide, hydrocarbons and nitrogen oxides, but does not remove carbon dioxide (CO2).
- Neglecting engine warnings and continuing to drive hoping the problem will go away — small faults can quickly develop into catalytic converter damage.
- Assuming all fuel additives are harmless to the catalytic converter; some ingredients can poison or clog the catalytic converter's surface.
Exam Tip
In theory questions you may be presented with statements about what damages the catalytic converter; choose options that mention leaded gasoline, ongoing misfires/oil contamination, or incorrect fuel additives. Pay attention to wording about what the catalytic converter does not do (e.g. it does not reduce CO2).
Did You Know?
Catalytic converters contain small amounts of precious metals, such as platinum, palladium and rhodium, which make them effective for exhaust cleaning — and, unfortunately, also a target for theft.
Frequently Asked Questions
What does the catalytic converter do in practice?
The catalytic converter converts harmful exhaust components (such as carbon monoxide, unburned hydrocarbons and certain nitrogen oxides) into less harmful substances through chemical reactions on a catalytic surface.
How do I know if the catalytic converter is broken?
Symptoms include reduced engine performance, an unpleasant rumbling or the smell of burned material, higher fuel consumption and an engine warning light on the dashboard. A workshop can perform a more accurate inspection and measurement.
Can the catalytic converter be repaired or does it need to be replaced?
In many cases a damaged catalytic converter is replaced with a new or approved used unit. Minor issues can sometimes be resolved by fixing the underlying engine problems that caused the damage.
Does leaded gasoline damage the catalytic converter?
Yes — lead-containing substances can poison the surface of the catalytic converter and render it ineffective. Driving theory may mention leaded gasoline as a historical example of what damages catalytic converters.
Is it illegal to remove the catalytic converter?
Removing or manipulating exhaust-cleaning equipment so that emissions increase can make the vehicle illegal to drive and cause problems during inspection. Specific rules and approval requirements may vary depending on the vehicle and modification.
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