Particulate filter removal is illegal - yet cars can still pass inspection

Since Euro 5 came into force in September 2009, Diesel engines have been required to use a particulate filter (FAP/DPF). More recently, when Euro 6c took effect in September 2017, the requirement for a particulate filter (OPF) was extended to petrol cars as well.

Why particulate filters (FAP/DPF and OPF) create headaches for owners

Although these filters are highly effective at trapping and burning off soot (particles) from exhaust gases - which are extremely harmful to human health - particulate filters have also become associated with faults and costly repairs.

As a result, many owners have chosen to remove the system. It is easy to find online adverts for garages offering both the physical removal and electronic deactivation of the particulate filter.

However, removing a particulate filter is illegal, even though it may still be possible to pass an inspection without the device.

Passing the vehicle inspection without a filter

In Portugal, the vehicle roadworthiness inspection is originally a function of the State, delegated to inspection centres. It is an exercise of public authority, carried out under procedures set out in law and using approved equipment - and that is where the issue lies.

At present, the procedures and the equipment needed to enforce checks on particulate filters are not regulated. Inspection centres largely limit themselves to measuring exhaust-gas opacity using an opacimeter. The applicable limit is the one stated by the manufacturer; if it is not available, a value such as 0.7 m⁻¹ may be applied for newer vehicles.

If a vehicle meets that opacity limit - which is straightforward - it can be approved even if the filter has been removed. That does not make the practice legal; it simply exposes a weakness in the current enforcement model.

FAP-off may be coming to an end

The pledge is not new, and the launch of a new inspection enforcement model has been repeatedly postponed. But it now appears the change is finally happening.

ACAP - the Portuguese Automobile Association - has said that the Government is currently regulating the introduction of this equipment via the IMT (Institute for Mobility and Land Transport), which has direct oversight of inspection centres.

"We received a communication stating that the particle counter is in the implementation phase at vehicle roadworthiness inspection centres."

Hélder Pedro, ACAP secretary-general.

New particle-count equipment and OBD electronic checks

This includes the approval of new exhaust-gas measurement equipment and electronic verification via the OBD system.

These tools make it possible to detect emissions above the legal limit of 250,000 particles per cubic centimetre, applicable to vehicles type-approved to Euro 5b or higher. Until then, the situation remains paradoxical: it is illegal, yet it is still possible to pass the inspection without a particulate filter.