Vehicle Emissions Diagnostics in Sunbury-on-Thames
An MOT emissions failure or emissions warning light means the engine or its after-treatment isn’t working as it should. The cause could be the engine itself or systems like the DPF, EGR, SCR or catalytic converter.
We diagnose emissions faults systematically and repair them correctly.
Common signs
Symptoms worth checking
- MOT emissions failure
- Excessive smoke
- Emissions-related warning lights
- Poor fuel economy
How emissions systems connect
Engine combustion quality affects everything downstream. A faulty injector can overload a DPF; an EGR fault raises NOx; a misfire damages catalysts.
Diagnosis starts with the engine and works through the after-treatment.
What we check
- Combustion and fuelling data
- Lambda and NOx sensors
- Catalyst efficiency
- DPF, EGR and SCR status
What we can do
- Emissions diagnostics
- Sensor and component repair
- Pre-MOT emissions checks
How it works
The process
- 01
Scan and test.
- 02
Identify cause.
- 03
Repair.
- 04
Verify emissions.
Why The Factory
Main-dealer capability, independent service
A Master Technician-led workshop with seven mechanical ramps, a dedicated MOT ramp and dealer-level diagnostics. Faults are shown to you and additional work is quoted before it goes ahead.
We stand behind the work we carry out. Parts and workmanship are covered in accordance with your statutory rights and any applicable manufacturer or supplier warranty. Please ask us for details relevant to your repair.
- On-site MOT testing
- Dealer-level diagnostics
Free local collection & return
Available by arrangement within approximately five miles of our Sunbury-on-Thames workshop. Further afield? Just ask us.
FAQs
Emissions Diagnostics: your questions answered
Why did my car fail the MOT emissions test?
Engine running faults, sensor issues, catalyst problems or DPF/EGR faults are common causes.
What can cause excessive exhaust smoke?
Blue: oil burning. Black: excess fuel. White: coolant or condensation.
Can an engine fault increase emissions?
Yes — misfires and fuelling faults directly affect emissions.
How are DPF, EGR and SCR systems related to emissions faults?
They each control specific pollutants; a fault in one can affect the others.
Can you diagnose emissions warning lights?
Yes.
Related services
DPF Diagnostics & Cleaning
Proper diagnosis of DPF warnings, cleaning and repair — never deletion.
EGR Repairs
EGR valve and cooler diagnosis and repair.
AdBlue / SCR Repairs
Legitimate diagnosis and repair of AdBlue warnings and countdowns.
MOT Test Centre
Class 4 & 7 MOT testing on site.
Need help with emissions diagnostics?
Send your registration and a quick description on WhatsApp, or call the workshop.
The Factory, Harris Way, Sunbury-on-Thames TW16 7EL