The Difference Between Euro 5 and Euro 6 Diesel Engines

With growing concerns about vehicle emissions, stricter regulations have been introduced over the years to reduce air pollution. In Europe, diesel engines are classified under Euro emissions standards, which set limits on the amount of pollutants vehicles can emit.

Two of the most widely discussed standards are Euro 5 and Euro 6. Many vehicle owners and fleet operators want to understand the differences between Euro 5 and Euro 6 diesel engines, how these regulations impact performance, and whether upgrading to Euro 6 is necessary.

This guide will break down the key differences, focusing on emissions, fuel efficiency, technology, and legal compliance.

1. What Are Euro Emissions Standards?

The Euro emissions standards were introduced in 1992 to regulate the levels of pollutants produced by vehicles across Europe. Each new Euro stage imposes stricter limits on harmful emissions such as:

• Nitrogen Oxides (NOx): Contribute to smog and respiratory problems
• Particulate Matter (PM): Tiny particles that impact air quality
• Carbon Monoxide (CO): A toxic gas harmful to humans and the environment
• Hydrocarbons (HC): Pollutants that contribute to ground-level ozone

Every new Euro emissions standard requires vehicle manufacturers to develop cleaner engines with advanced emissions control technologies.

2. What is a Euro 5 Diesel Engine?

Euro 5 Regulations (Introduced in 2009)

The Euro 5 emissions standard was introduced in September 2009 and became mandatory for all new diesel cars from January 2011. It significantly reduced particulate emissions compared to Euro 4 and mandated the introduction of Diesel Particulate Filters (DPF).

Key Emissions Limits for Diesel (Euro 5):

• NOx (Nitrogen Oxides): 180 mg/km
• PM (Particulate Matter): 5 mg/km

Technology Used in Euro 5 Diesel Engines:

• Diesel Particulate Filter (DPF): Required to trap soot and reduce particulate emissions
• Common Rail Injection: Improved fuel atomization for lower emissions
• Turbocharged Efficiency: More refined turbo technology for power and fuel economy

Although Euro 5 diesel engines significantly reduced soot emissions, they still produced higher NOx emissions, which led to stricter Euro 6 standards.

3. What is a Euro 6 Diesel Engine?

Euro 6 Regulations (Introduced in 2014)

The Euro 6 emissions standard was introduced in September 2014 and became mandatory for all new diesel vehicles from September 2015. The most notable improvement was a 55 percent reduction in NOx emissions compared to Euro 5. To achieve this, diesel vehicles had to adopt Selective Catalytic Reduction (SCR) and AdBlue systems.

Key Emissions Limits for Diesel (Euro 6):

• NOx (Nitrogen Oxides): 80 mg/km
• PM (Particulate Matter): 4.5 mg/km

Technology Used in Euro 6 Diesel Engines:

• Selective Catalytic Reduction (SCR): Uses AdBlue (Diesel Exhaust Fluid) to neutralize NOx emissions
• Diesel Particulate Filter (DPF): Improved efficiency to meet stricter PM limits
• Exhaust Gas Recirculation (EGR): Recirculates a portion of exhaust gases to lower combustion temperatures and NOx emissions
• Advanced Fuel Injection: More precise fuel metering for better combustion and lower emissions

Euro 6 diesel engines are significantly cleaner than Euro 5, making them compliant with Ultra Low Emission Zones (ULEZ) and other clean air regulations.

4. Key Differences Between Euro 5 and Euro 6 Diesel Engines

Euro 6 diesel engines offer far lower NOx emissions and are required for compliance with ULEZ and Clean Air Zones (CAZ) in cities such as London, Birmingham, and Manchester.

5. Will Euro 5 Diesel Cars Be Banned?

Although Euro 5 diesel vehicles are still allowed on the road, many UK cities now charge them for entering Low Emission Zones (LEZ) and ULEZ areas. While they are not completely banned, they are subject to daily charges that can add up significantly.

• London ULEZ Charge: £12.50 per day for non-Euro 6 diesel vehicles
• Birmingham CAZ Charge: £8 per day for non-Euro 6 diesels
• Greater Manchester CAZ: Set to introduce charges for older diesel vehicles

For details on compliance and fees, visit Transport for London’s ULEZ website.

If your vehicle is Euro 5 or older, upgrading to Euro 6 diesel may help avoid emissions charges and ensure long-term compliance with environmental regulations.

6. Should You Upgrade to a Euro 6 Diesel?

Upgrade to Euro 6 If:

• You frequently drive in ULEZ or Clean Air Zones
• You want better fuel efficiency and lower NOx emissions
• You need a vehicle with strong resale value
• You are a fleet operator required to meet emissions regulations

Stick with Euro 5 If:

• You primarily drive on motorways and rural areas
• You want to avoid AdBlue maintenance
• You are looking for a budget-friendly used diesel

For urban drivers, Euro 6 diesel is the best option for avoiding emissions penalties. However, for long-distance motorway users, a well-maintained Euro 5 diesel still offers strong performance and efficiency.

Conclusion

The difference between Euro 5 and Euro 6 diesel engines lies mainly in emissions control and compliance with ULEZ regulations. While Euro 5 diesel vehicles remain efficient and cost-effective, Euro 6 engines are significantly cleaner and future-proof for low-emission zones.

If you own a Euro 5 diesel and frequently drive in cities, upgrading to Euro 6 can help avoid emissions charges and ensure better long-term value.