BS4 vs BS6

Understanding the difference between BS4 and BS6 is important whether you are buying a new bike, upgrading your vehicle, or simply trying to understand how India is tackling air pollution.

What are Bharat Stage Emission Standards (BSES)?

Bharat Stage Emission Standards (BSES) are a set of regulations introduced by the Government of India to control the level of air pollutants emitted by internal combustion engines used in motor vehicles. These standards are enforced by the Central Pollution Control Board (CPCB), which operates under the Ministry of Environment, Forest and Climate Change.

History of Emission Standards in India?

• 2000: India 2000: The first national emission standard introduced (equivalent to Euro 1).
• 2005: BS2 (Bharat Stage 2): Tighter controls on hydrocarbons and NOx.
• 2010: BS3 (Bharat Stage 3): Further reductions in pollutants; sulphur content capped at 150 ppm.
• 2017: BS4 (Bharat Stage 4): Sulphur limit reduced to 50 ppm; new emission-control technologies introduced.
• 2020: BS6 (Bharat Stage 6): BS5 skipped entirely; sulphur reduced to just 10 ppm, advanced after-treatment systems mandated.

What is Bharat Stage 4 (BS4)?

BS4, or Bharat Stage 4, is the fourth stage of India's vehicle emission standards. It came into force in April 2017 and replaced BS3 across the country. BS4 vehicles were required to comply with significantly stricter pollution norms compared to their predecessors. 

Some of the key features of BS4 vehicles are given below: 

• Sulphur content in BS4 fuel was capped at 50 parts per million (ppm), a reduction from 150 ppm under BS3. 
• Introduced the Automatic Headlamp On (AHO) feature, which kept headlamps running at all times for improved road safety. 
• Vehicles were fitted with an Electronic Control Unit (ECU) to manage ignition timing and fuel delivery more precisely. 
• Improved catalytic converters and basic Exhaust Gas Recirculation (EGR) systems were introduced to reduce emissions at the exhaust pipe. 
• Oxygen sensors helped monitor and fine-tune the air-fuel mixture in real time. 
• Onboard Diagnostic (OBD) systems were present in some BS4 vehicles but were not universally mandatory. 
• No requirement for a Diesel Particulate Filter (DPF) or Selective Catalytic Reduction (SCR) system.

What is Bharat Stage 6 (BS6)?

BS6, or Bharat Stage 6, is the sixth and most stringent emission standard currently in force in India. It became mandatory for all new vehicles from 1 April 2020. 

Notably, India skipped the BS5 stage entirely – a decision taken by the Government in 2016, in order to align more quickly with international pollution standards and address the country's rapidly worsening air quality. 

BS6 is broadly equivalent to the Euro VI standard used in Europe and demands a dramatic reduction in harmful exhaust gases such as nitrogen oxides (NOx) and particulate matter (PM), alongside a fivefold improvement in fuel cleanliness. 

Some of the key features of BS4 vehicles are given below: 

• BS6 fuel contains just 10 ppm of sulphur – five times cleaner than BS4 fuel (50 ppm), enabling advanced emission-control systems to function effectively.
• Mandatory fitment of Diesel Particulate Filters (DPF) in diesel vehicles to capture soot and particulate matter before it leaves the exhaust.
• Selective Catalytic Reduction (SCR) systems use a urea-based solution (AdBlue) to convert harmful NOx gases into harmless nitrogen and water.
• Enhanced Exhaust Gas Recirculation (EGR) systems to further limit combustion-related emissions.
• Mandatory Onboard Diagnostics II (OBD-II) systems that continuously monitor emission-related components and alert the driver if any fault is detected.
• Real Driving Emissions (RDE) testing was introduced alongside BS6, measuring actual on-road emissions rather than relying solely on laboratory tests.
  
• Despite the lower sulphur content, BS6 fuels contain specially formulated additives that compensate for the reduced natural lubrication provided by sulphur.

BS4 vs. BS6 – Comparison

BS4 vs. BS6 – Engine Technology Differences

BS4

• Basic catalytic converter 
• Conventional EGR (Exhaust Gas Recirculation) 
• Multi-point fuel injection 
• Electronic Control Unit (ECU) 
• Oxygen sensor for air-fuel monitoring 
• Automatic Headlamp On (AHO) – safety feature 
• No DPF or SCR required 
• OBD present in select vehicles only 

BS6 

• Advanced catalytic converter 
• Enhanced EGR system 
• High-pressure direct injection 
• Diesel Particulate Filter (DPF) 
• Selective Catalytic Reduction (SCR) 
• Mandatory OBD-II diagnostics 
• Real Driving Emissions (RDE) monitoring 
• Fuel additives to replace sulphur lubrication

Impact on Vehicle Performance and Fuel Effecienc

Petrol BS6 Vehicles

• Most BS6 petrol engines – including those in motorcycles and scooters – feel smoother and more refined thanks to advanced fuel injection systems. 
• There may be a marginal improvement in fuel efficiency in some models due to cleaner combustion. 
• Power output is broadly comparable to BS4, with some models showing minor gains in midrange torque. 
• BS6 petrol engines typically require little additional maintenance compared with their BS4 equivalents. 

Diesel BS6 Vehicles

• The addition of DPF, SCR, and enhanced EGR systems adds complexity to the engine bay and may result in a slight reduction in fuel economy. 
• Emissions are vastly cleaner – up to 70% less NOx and 82% less particulate matter than BS4 diesel vehicles. 
• Diesel vehicles with DPFs require occasional highway driving to allow the filter to regenerate (burn off accumulated soot). Purely urban driving can occasionally cause DPF clogging, though this has been largely addressed through improved engine management software. 
• Maintenance costs for BS6 diesel vehicles may be slightly higher due to the additional emission-control components.

Benefits of BS6 over BS4

• Significantly Cleaner Air: BS6 vehicles emit up to 70% less NOx (diesel) and 25% less NOx (petrol) than their BS4 counterparts. The reduction in particulate matter is even more dramatic, helping to reduce smog and improving air quality in cities.
• Better Public Health Outcomes: Fine particulate matter (PM2.5 and PM10) is linked to a range of serious respiratory and cardiovascular conditions. By setting stringent PM limits for the first time on petrol vehicles and drastically reducing them for diesel, BS6 norms contribute directly to fewer pollution-related illnesses.
• Five Times Cleaner Fuel: The reduction in sulphur content from 50 ppm to 10 ppm makes BS6 fuel substantially purer. This cleaner fuel not only reduces harmful emissions but also extends the life of emission-control components.
• Real-World Accountability: The introduction of Real Driving Emissions (RDE) testing means vehicle manufacturers can no longer rely solely on laboratory tests. Vehicles must meet emission standards in actual on-road conditions, providing a more accurate reflection of environmental impact.
• Enhanced Engine Technology: The engineering required to meet BS6 norms has pushed manufacturers to develop more efficient, reliable, and technologically advanced engines, benefiting consumers in the long run.
• Global Alignment: BS6 aligns India with Euro VI – one of the most rigorous emission standards in the world. This makes Indian-manufactured vehicles more competitive in global markets and positions India as a serious player in clean mobility.
• Reduced Carbon Footprint: While BS6 primarily targets NOx and PM, the cleaner combustion enabled by low-sulphur fuel also contributes to a modest reduction in carbon dioxide and carbon monoxide emissions.

Existing BS4 Vehicles

• If you already own a BS4 vehicle, you can continue to drive it legally on Indian roads, provided it has a valid registration and passes regular Pollution Under Control (PUC) checks.
• No new BS4 vehicles can be sold or registered in India as of 1 April 2020.
• The restriction is on the sale and registration of new BS4 vehicles only – there is no ban on driving or owning existing ones.
• You can use BS6 fuel in your BS4 vehicle without any issue; however, the vehicle itself will not meet BS6 emission standards as it lacks the required after-treatment technology.
• Pre-owned BS4 vehicles remain available in the used-vehicle market and may still be a cost-effective option, provided they meet PUC norms.

A good credit score can help you secure lower interest rates on loans and credit cards.

Get Free Credit Score