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Bs4 was brought into force in the year 2017 by The Bharat Stage Emission Standards (BSES) to make emission standards more rigid. The BS6 emission norms came into effect in 2020, with the aim to reduce pollution even further compared to the BS4 standards.


The key difference between Bs4 and Bs6 is that under Bs6 Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) have been established which were not present earlier. Another fundamental difference between Bs4 and Bs6 is in terms of sulphur and nitrogen oxide emissions. Another striking feature of Bs4 vs Bs6 is that Bs6 compliant engines are required to be filled with Bs6 fuel and not the Bs4 fuel.


The Bharat Stage Emission Standards (BSES) are government-set regulations imposed on vehicular emissions of all types in India. The first set of emission norms was enforced by the government in the year 2000, known as ‘India 2000’. In this article, we will look at the difference between BS4 vs BS6 emission norms. Let’s get started.

What is BS4 (BS-IV)?

In 2017, the BSES brought Bharat Stage 4 (BS4 or BS-IV) into effect with the primary focus on making emission standards more stringent. Some of the changes related to emission in BS4 involve ignition control, tailpipe emission, Electronic Control Unit (ECU), and so on. One of the most significant changes introduced under the BS4 was the Automatic Headlamp On feature, which takes into account the safety aspect of the emission standards.

What is BS6 (BS-VI)?

The standards to maintain vehicle emissions’ output in India are set by the Central Pollution Control Board, while the BSES regulates the pollutant output from vehicles. The BS6 emission norms came into effect in 2020, with the aim to reduce pollution even further compared to the BS4 standards.


Now, it’s time to understand the difference between BS4 vs BS6 emission norms.

BS4 vs BS6 Engines- What is the Difference?

Here are a few key differences between BS4 and BS6 emission norms:


  • With the implementation of BS6 standards, Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) have been established as well. This was not present in the previous BS norms.

  • Along with the implementation of BS6 emission norms, India is all set to introduce the Real Driving Emission (RDE). It is said to measure the real-time emission from vehicles against laboratory conditions. The same was not a part of BS4 emission norms.

  • Onboard Diagnostics (OD) is now mandatory for all vehicles under the BS6 emission norms.

  • As the BS6 emission norms come into play from April 1, 2020, there is also a change in the fuel used in vehicles. Thus, the vehicles that are BS6-compliant will require BS6 fuel. If the vehicles happen to use BS4-grade fuel, they will not adhere to the BS6 emission norms. Likewise, if BS4-compliant vehicles use the BS6 fuel, their engine will be affected, and emissions will increase.

  • Another crucial difference between the two is in terms of sulphur and nitrogen oxide emissions. The trace of sulphur in BS6 fuel is five times lesser than in BS4 fuel. Moreover, nitrogen oxide levels of BS6 diesel and petrol engines are said to be brought down by 70% and 25%, respectively.


To understand what is the difference between BS4 vs BS6 emission norms, consider the following table:

Fuel Type




Petrol-Based Vehicles

Nitrogen Oxide (NOx)

80 mg

60 mg

Particulate Matter (PM)


4.5 mg/km

Diesel-Based Vehicles

Nitrogen Oxide (NOx)

250 mg

80 mg

Particulate Matter (PM)

25 mg

4.5 mg/km

HC + NOx

300 mg/km

170 mg/km

How Does the BS6 Diesel Engine Work?

In technical terms, the Selective Catalytic Reduction (SCR) unit converts nitrogen oxide (NOx) to diatomic nitrogen and water (harmless entities). The SCR unit uses AdBlue or diesel exhaust fluid to reduce NOx emission. This fluid is made up of urea and deionised water. So, when the exhaust gases get mixed with this fluid, urea is converted into ammonia and CO2. Further, ammonia converts NOx into nitrogen and water vapour. Overall, this process helps reduce the content of pollutants from vehicular emissions.


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Health and Environmental Consequences of Vehicle-Generated Air Pollution in India

Air pollution caused due to vehicle-generated emissions can have immediate and long-term effects on the environment. As stated earlier, motor vehicles emit several harmful gases and particulate matter, which leads to air pollution.


Following are the consequences of vehicle-generated air pollution:

  • Global Warming

One of the major consequences of air pollution due to vehicle emissions is global warming. Motor vehicles emit carbon dioxide and other harmful gases that contribute to pollution levels. Since these harmful gases stay trapped in our environment, it leads to a rise in overall temperatures across the world i.e., global warming. Furthermore, this increase in temperature can have adverse effects on farming, wildlife, sea levels, and landscapes.

  • Impact on Air, Soil & Water

Vehicle-generated air pollution can affect the quality of air, soil, and water in our environment. One of the harmful gases emitted by motor vehicles is nitrogen oxide, which leads to the depletion of the ozone layer. The ozone layer protects our earth and its environment from the harmful UV rays of the sun. On the other hand, sulphur dioxide and nitrogen dioxide mix with rainwater to produce acid rain, which further affects farming, forests, and our infrastructure. Oil and fuel spills from motor vehicles can seep into the earth, affecting cultivation. Further, when the same is discarded in the water, it can contaminate water bodies and disrupt marine life.

  • Impact on Human Health

Much like the environment, humans are vulnerable to these harmful pollutants as well. People across India suffer from several health issues caused due to breathing unhealthy air. As such, there has been a significant rise in skin infections, allergies, and respiratory issues over the last few years. Moreover, the harmful emissions from motor vehicles can even lead to heart diseases in senior citizens and infants.


We hope this article helped you understand the difference between BS4 vs BS6 bike and car engines. So, if you are planning to buy a new vehicle this year, you will be well informed to make the right decision.


Just like choosing between BS4 vs BS6 engines is imperative to stay compliant with the emission norms, it is also essential to choose an ideal vehicle insurance plan. Selecting the right car insurance plan will allow you to financially safeguard your vehicle in case of an accident. In fact, you can compare different vehicle insurance plans online and choose one that fulfils all your requirements.


Download the Bajaj Markets’ Car Insurance App to choose an insurance plan that best suits your needs. You can also check the premiums on car insurance plans available on Bajaj Markets by using our car insurance calculator. The tool not only provides premium quotes but also allows you to compare quotes from different insurers. Based on the results, you can then choose a car insurance plan that is affordable and meets your requirements.

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FAQs on Difference between BS4 vs BS6 Engines

 If BS4-compliant vehicles are filled with BS6 fuel, it may affect the engine and increase the emission.

 While BS6-compliant vehicles can run on BS4 fuel, they will not comply with the BS6 emission norms.

The prices of BS6 and BS4 fuels are not significantly different. However, after BS6 is implemented across the nation, the prices may fluctuate. This is due to input costs incurred by the Oil Marketing Companies (OMCs) when updating facilities on their side.

 No, it is illegal to convert your old car to fit the BS6 emission norms.

 Yes, according to the Motor Vehicle Act, all cars require a Pollution Under Control (PUC) certificate to ply on Indian roads.

 Compared to BS4 fuel, BS6 fuel is cleaner since it contains less sulphur, which leads to lower pollution or emissions.

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