Why does my Mercedes-Benz S-Class fail emission tests in Pakistan despite regular servicing?

Home > Gari Forums > Mercedes Benz Forums > Mercedes Benz S Class Forums > Mercedes Benz S Class Emissions Issues Forums

Post a New Topic

Why does my Mercedes-Benz S-Class fail emission tests in Pakistan despite regular servicing?

Many owners find their S-Class failing emission tests even after routine maintenance. This can be caused by malfunctioning oxygen sensors, clogged catalytic converters, faulty EGR Exhaust Gas Recirculation valves, o r software issues in the engine control unit ECU that affect fuel-air mixture and exhaust cleanliness.

Talha Kyanii asked on 11 Oct 2025 16:13:21 pm

1 Answer

9 views |

Gari Master - on 11 Oct 2025 16:14:30 pm

Failing emission tests despite regular servicing can be due to:

Malfunctioning Oxygen Sensors: These sensors monitor oxygen levels in the exhaust and adjust the fuel-air mixture. Faulty sensors cause incorrect readings and poor combustion.

Clogged Catalytic Converter: Over time, carbon buildup o r damage reduces the converter’s efficiency in cleaning exhaust gases.

Faulty EGR Valve: A stuck o r malfunctioning Exhaust Gas Recirculation valve can lead to higher nitrogen oxide emissions.

ECU Software Issues: The engine control unit might not manage fuel injection o r ignition timing properly due to outdated o r corrupted software.

Suboptimal Maintenance Practices: Use of incorrect fuel, filters, o r ignoring other engine problems can also affect emissions.

Thorough diagnostics and component replacements o r software updates at authorized service centers help pass emission tests.