Practical guide on what to do with the fap light on

Once the FAP light comes on, it is good to know what to do : here’s what to do .

FAP light: what it indicates

Most modern diesel cars are equipped with an anti-particulate filter, but not everyone knows what to do when the relative warning light comes on on the dashboard: do you need to stop immediately? Let’s go in order.

First of all we remind you that the task of the particulate filter is to retain the particulate matter from the exhaust gases, preventing it from being released into the atmosphere.

Car manufacturers provide for constant monitoring of the filter, which takes place with 2 sensors: they measure the pressure difference upstream and downstream, and when this variation is too high, the control unit intervenes and starts a cleaning (or regeneration) cycle.
The goal is to raise the temperature inside the filter up to about 550 ° C, so as to incinerate the particulate and allow the unblocking of the FAP: when the so-called regeneration does not take place correctly, the warning light turns on Particulate filter.

FAP warning light: new and old cars

Remember that there is no standard regeneration strategy, but it varies according to the year of production and the vehicle manufacturer: on older cars (early 2000s) the particulate filter light on the dashboard indicates only regeneration filter in place. What to do in this case?

First of all, do not stop : indeed, it would be better to travel along high-speed roads with the engine at a speed of about 3,000 rpm, at least until the warning light goes out: this indicates that the process has been successful.

Unfortunately, some people often think it is a failure and turn off the engine, abruptly stopping the regeneration of the filter .

For this reason, the most modern cars do not provide for the switching on of the fap light, in order to limit interrupted and deleterious regenerations to the maximum.

A tip: to better understand how the FAP regeneration process works, we invite you to read the instruction booklet of your car.

FAP light: how to solve the problem

On diesel cars of any age, you really only have to worry if the engine light comes on together with the particulate filter warning light , with a simultaneous reduction in performance: in fact, this state usually indicates the natural regeneration cycles have not been successful and it is necessary to proceed with a forced regeneration in the workshop.

Some workshops attempt a forced regeneration with a diagnostic tool, others washing the filter with special products. If you need to replace a filter, know that the cost is about 1,500 euros, while its regeneration costs about 500.

We remind you that eliminating the FAP is an illegal choice .

A note: on some cars, especially if they are of large dimensions, in addition to the anti-particulate filter, a catalyst is mounted to reduce nitrogen oxides (NOx), so as to reach the Euro6 standard. The warning light is often generically related to the anti-pollution system, so it could also indicate a low quantity of the Ad-Blue liquid.


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