ULEZ Retrofits: Can You Actually Upgrade Your Exhaust to Euro 6?

"Can I just fit the Euro 6 bits?"

That's the question mechanics are hearing daily. Drivers see Euro 6 vehicles on the road. Those vehicles have AdBlue tanks, SCR catalysts, and NOx sensors. Parts that can be purchased. So why can't you just fit them to your Euro 5 diesel?

It’s because your car wasn't designed for it, the certification process costs tens of thousands, and even if you managed it mechanically, the DVLA wouldn't recognise it - this is the short answer.

The long answer involves understanding why Euro 6 is a complete system redesign, not a parts upgrade. And why the retrofit certification that works for commercial vans will never exist for your Golf, Focus, or Astra.

What Is Euro 6 

Introduced in September 2015, Euro 6 slashed permissible Nitrogen Oxide (NOx) emissions from 180mg/km (Euro 5) to just 80mg/km. That's a 55% reduction that couldn't be achieved by tweaking engines. It required active chemical processing of exhaust gases.

For ULEZ and Clean Air Zone compliance:

• Petrol vehicles: Euro 4 or higher (generally 2005 onwards)
• Diesel vehicles: Euro 6 only (generally September 2015 onwards)

Your compliance status comes from your original Type Approval, held by the DVLA and checked automatically by ANPR cameras. The cameras aren't sniffing your tailpipe. They're checking your registration against a database.

How Euro 6 Works

Here's why you can't just bolt on some better filters:

The SCR System

Euro 6 diesel vehicles use Selective Catalytic Reduction (SCR). AdBlue (a 32.5% urea solution) gets injected into hot exhaust gases. The heat breaks down the urea into ammonia, which then reacts with NOx inside a special catalyst, converting toxic emissions into harmless nitrogen gas and water vapour.

Simple? Not remotely.

A complete SCR system needs:

• AdBlue tank (10-20 litres)
• Heated delivery lines
• Dosing pump and injector
• SCR catalyst brick
• NOx sensors (two of them)
• Ammonia slip catalyst
• Standalone control unit

In a Transit van, there's room for all this. But in a Golf or Focus the underbody is packed solid. You'd be compromising fuel tank capacity or suspension mounting points.

The Temperature Problem

SCR only works above 200°C. During urban stop-start driving (exactly what ULEZ targets), exhaust temperatures are too low. Inject AdBlue when it's cold and it crystallises instead of converting, clogging your system with solid urea deposits.

Factory Euro 6 designs mount the SCR catalyst close to the engine to keep it hot. Retrofit systems go further back, losing critical heat. The fix is to use active heating elements. But it will cost you a lot!

The Computer Problem

Euro 6 vehicles have engine control units programmed for SCR. Euro 5 vehicles don't. Retrofit kits need a separate control unit to piggyback onto your existing sensors. It's a wiring nightmare across different vehicle models.

Why CVRAS Certification Kills Most Upgrades

Even if you could mechanically install an SCR system, the next problem is CVRAS certification.

The Clean Vehicle Retrofit Accreditation Scheme (CVRAS), run by the Energy Saving Trust, is the only way to change your vehicle's emissions classification. ANPR cameras check your DVLA record, not your emissions. No CVRAS certificate means no DVLA update means £12.50 daily charges forever.

To get CVRAS approval, systems must pass Portable Emissions Measurement System (PEMS) testing on actual roads in varied conditions. Not in a lab. On urban streets, rural roads, and motorways. In different temperatures. With different loads.

A single certification campaign costs tens of thousands of pounds.

The Energy Saving Trust is explicit: no CVRAS-approved retrofit systems exist for Euro 5 diesel passenger cars.

Approved systems exist only for:

• Specific commercial vans (Sprinter, Transporter T5)
• London taxis (TX4)
• Heavy goods vehicles and buses
• Land Rover Defender 2012-2015 (that's it for passenger cars)

Why? Each vehicle model needs separate engineering, calibration, and PEMS testing. With hundreds of passenger car variants worth £3,000-£6,000 each, the business case collapses instantly.

What's for Sale on Parts Marketplaces

Let's look at what platforms like ifndautoparts.com actually stock and what it means for ULEZ.

Mercedes ML 320 EGR Valve (£180-£250)

EGR valve with solenoid for Mercedes-Benz M-Class recirculates exhaust gases to lower combustion temperatures and reduce NOx in Euro 4 and Euro 5 engines.

Will it help with ULEZ? No. It'll fix a faulty EGR and restore your Euro 5 spec. That's it. You're still Euro 5.

Peugeot 3008 DPF and Catalytic Converter

This used combined diesel particulate filter and catalytic converter for a Peugeot 3008 Euro 5 diesel traps soot and burns hydrocarbons. Essential for MOT smoke tests.

The ULEZ problem: Handles particulate matter but can't touch the 80mg/km NOx threshold. You'll pass MOT. You won't pass ANPR.

The term "catalytic converter" fools people into thinking a better cat equals a higher emissions rating. These restore factory spec. They don't upgrade anything.

Mercedes GL350 NOx Oxygen Sensor

This NOx sensor for Mercedes-Benz GL-Class and E-Class Euro 6 diesel models measures NOx concentrations in the exhaust stream. On Euro 6 vehicles, these sensors monitor the SCR catalyst's performance and control AdBlue dosing.

This part is for Euro 6 owners to maintain existing compliance. When NOx sensors fail (and they do, around 50,000-80,000 miles), the SCR shuts down. Dashboard warnings appear. Eventually, the car refuses to start. Dealerships charge £400-£600 for replacement.

Finding used genuine sensors at £150-£200 helps Euro 6 owners stay compliant affordably. But these sensors do not upgrade non-compliant vehicles.

What You Can't Buy

Scroll through any parts site. You'll find sensors, valves, filters, DPFs, catalytic converters. All useful for maintenance. None are CVRAS-certified complete retrofit systems.

Those only come from specialist companies like HJS Emission Technology and Cybrand, sold through approved installers for £5,000-£7,000. They're complete exhaust replacements with integrated DPF/SCR, AdBlue tanks, heating elements, and vehicle-specific calibration. Professional installation includes DVLA notification.

They're not on general marketplaces because selling components separately invalidates CVRAS approval.

The Economics That Kill Passenger Car Retrofits

Let's talk money.

2012 Volkswagen Golf 2.0 TDI (Euro 5):

• Current value: £4,000-£5,000
• Theoretical retrofit cost: £6,000-£8,000
• Total investment: £10,000+ for a £4,000 car

2014 Mercedes Sprinter Van (Euro 5):

• Current value: £18,000-£25,000
• Actual retrofit cost: £6,000
• Makes economic sense

The fragmentation problem makes it worse. A "Ford Focus" might be five different engines, three body styles, multiple model years. Each needs separate PEMS certification at tens of thousands per variant. Multiply across hundreds of models. Impossible.

Government trials found another issue: retrofit SCR systems underperform in urban driving. They can't reach operating temperature during stop-start traffic, exactly where ULEZ compliance matters most. They work great on motorways. Useless in London.

The Illegal Shortcuts (Don't)

Desperate times breed bad decisions.

AdBlue emulators trick your ECU into thinking the SCR works when it doesn't. Dashboard warnings vanish. Emissions stay high. DVSA roadside checks catch this instantly with mobile analysers. £1,000 fines, invalid insurance, potential criminal record, - just not worth it. 

Non-approved "retrofits" from dodgy garages won't update your DVLA record. You'll have a cleaner car that still gets charged £12.50 daily.

What You Should Actually Do

If You Own a Passenger Car (Euro 5 Diesel or Euro 3 Petrol)

Accept it: you cannot retrofit to Euro 6 compliance.

Don't waste money on:

• EGR valves, DPFs, or cats marketed for ULEZ compliance
• "AdBlue delete" or "Euro 6 remap" services
• Parts from Euro 6 vehicles expecting them to upgrade yours

Do this instead:

• Check your vehicle at tfl.gov.uk (some late 2015 models actually are Euro 6)
• Apply for grants (Scotland: £2,000 disposal grant plus £1,000 travel vouchers)
• Calculate 50 ULEZ trips = £625/year. Compare to replacement costs.
• Consider replacement

If You Own a Van

Retrofitting works for specific commercial vehicles.

1. Check the CVRAS approved systems register for your van model
2. Compare £6,000 retrofit against £40,000+ replacement
3. Check grants (Scottish micro-businesses get 50% funding)
4. Use CVRAS-approved installers only
5. Verify DVLA records update

If You Own a Euro 6 Vehicle

These systems break. Maintain them properly.

Common failures: NOx sensors, AdBlue injectors, DPF regeneration issues affecting SCR performance.

Use the My Garage feature to find compatible parts. Stock spares before they fail. Use only proper AdBlue (32.5% urea). Monitor consumption for early fault detection.

FAQ: ULEZ Retrofits

Can I retrofit my diesel car to Euro 6 for ULEZ compliance? No. For passenger cars, no CVRAS-approved Euro 6 retrofit systems exist. Only specific vans, taxis, buses, and rare exceptions like certain Land Rover Defenders have approved options.

How much does a Euro 6 retrofit cost? For the limited vehicles where they exist (commercial vans, taxis), £5,000-£7,000 including installation. For passenger cars, retrofits aren't available at any price.

Will replacing my DPF make my car ULEZ compliant? No. DPF replacement restores your Euro 5 spec but can't upgrade to Euro 6. Euro 6 requires SCR technology with AdBlue. Without CVRAS certification, no parts replacement prevents ULEZ charges.

What is CVRAS certification? The only certification Transport for London accepts for changing emissions classification. ULEZ cameras check your DVLA record through ANPR. Without CVRAS updating that record, you'll still face daily charges regardless of what you've fitted.

Are there grants for retrofits or replacement? Scotland's LEZ Support Fund offers £2,000 disposal grants plus £1,000 travel vouchers. Scottish micro-businesses get 50% funding for CVRAS van retrofits. London's scrappage scheme closed September 2024. Bristol offers up to £1,500 for cars, £4,500 for vans. Check your local authority as these change frequently.

The Bottom Line

The sensors, valves, filters available on car parts marketplaces all maintain existing vehicles. None upgrade your emissions classification.

The reason is simple: passenger car Euro 6 retrofits don't exist because they can't exist. Technical packaging is impossible. Certification costs are prohibitive. Economics don't work.

Your realistic options:

1. Check if your vehicle actually qualifies (some late 2015 diesels do)
2. Apply for available grants
3. Replace with Euro 6 or newer
4. Pay charges for occasional urban use
5. Keep the car for non-ULEZ driving only

The parts market keeps vehicles maintained and existing Euro 6 systems working. It can't provide regulatory solutions for non-compliant passenger cars.

Need maintenance parts or advice? Browse emission control components in our exhaust category by vehicle, or use the My Garage tool to filter compatible parts. 

Key Resources

1. Transport for London ULEZ Vehicle Checker
   Check your vehicle's compliance status
   https://tfl.gov.uk/modes/driving/check-your-vehicle/
2. Energy Saving Trust, Clean Vehicle Retrofit Accreditation Scheme
   Official CVRAS guidance and approved systems list
   https://energysavingtrust.org.uk/service/clean-vehicle-retrofit-accreditation-scheme/
3. Transport Scotland, Low Emission Zone Support Funding 2025-26
   Disposal grants and retrofit funding for Scottish residents https://www.transport.gov.scot/news/2-million-for-low-emission-zone-support-funding-in-2025-26/
4. Low Emission Zones Scotland, Funding Information
   Detailed eligibility criteria for household and micro-business grants
   https://www.lowemissionzones.scot/funding