An exhaust emissions test measures the gases released from a vehicle’s exhaust system to determine whether the engine is operating efficiently and within legal environmental limits. During an MOT, vehicles must pass an emissions test to comply with DVSA requirements. If emissions exceed the permitted limits, the vehicle will fail until the underlying fault has been repaired.

Petrol Exhaust Gas Analysers

Petrol vehicles are tested using an exhaust gas analyser, which samples gases directly from the exhaust pipe.

A petrol analyser measures Carbon Monoxide (CO), Hydrocarbons (HC), Carbon Dioxide (CO₂), Oxygen (O₂) and Lambda (air/fuel ratio).

Diesel Smoke Meters

Diesel vehicles are tested differently. Rather than measuring combustion gases in the same way as petrol vehicles, a diesel emissions check measures smoke opacity, which is the amount of light blocked by exhaust smoke during acceleration.

Combined Petrol and Diesel Emissions Analysers

Many garages choose a combined emissions analyser, allowing technicians to test both petrol and diesel vehicles using a single workstation. These systems are particularly useful for busy workshops and MOT bays.

How to Perform an Engine Exhaust Emissions Check

1. Warm The Engine. The engine should be at normal operating temperature before testing, as a cold engine can generate inaccurate results.

2. Connect The Equipment. The analyser probe is inserted securely into the vehicle’s exhaust pipe. Some modern emissions analysers also connect to the vehicle via OBD to obtain engine speed and other operating data automatically.

3. Carry Out The Test. For petrol vehicles, the analyser records gas concentrations while the engine runs at specified idle and fast-idle speeds. For diesel vehicles, the smoke meter performs an opacity test during controlled engine acceleration.

4. Review The Results. The analyser produces a report showing whether the vehicle has passed or failed.

Find the Right Emissions Tester for Your Garage

Whether you’re equipping a new workshop or upgrading an existing MOT bay, selecting the right emissions tester is vital. Choosing high-quality garage equipment helps improve efficiency while ensuring accurate, repeatable test results.

Whether you need a petrol exhaust gas analyser, diesel smoke meter or a combined emissions analyser, Concept Garage Equipment can help you choose the right solution for your workshop.

Call our friendly team today on 01302 203 888 or use the online contact form.