Low FAP additive level: causes, consequences and solutions

Last updated on February 13, 2025 by Maxime De Presster

THE Particles filter (FAP) It is a key element of the Diesel vehicle exhaust system, designed for Reduce pollution emissions. When the message «Weak FAP fat» appears on your dashboard, this means that theAdditive destined to facilitate FAP’s regeneration It is insufficient.

This ultra-common guide explains you Because this message appears, what are the consequences of a low level of additive and how to remedy effectively.

Why is the message «FAP level level» is displayed?

The FAP additive is a special liquid, generally Cérine or AdblueAdded to fuel to help burn sooting particles in the particle filter.

🔹 Main causes of a low level of FAP additives:
✔ Almost empty additive tank : The additive was consumed after several tens of thousands of kilometers.
✔ Loss or defect of the additive tank : Dysfunction can cause additive loss.
✔ Defective level sensor : A probe can send a false notice even if the level is correct.

📌 To know : Filling the FAP additive is generally necessary 80,000 to 120,000 kmdepending on the vehicle model.

What are the consequences of a low level of FAP additive?

AND Insufficient level additive causes problems of Regeneration of the particles filterwhich can cause:

❌ Fap Fouling → risk of clogging and loss of power
❌ Gradient engine mode → the calculator reduces the power supply to avoid damaging the engine
❌ Increase in fuel consumption → The strength engine to compensate for the clogged fap
❌ Light of the engine on → an intervention becomes necessary quickly

🚨 If the FAP additive is not updated, the FAP can be completely clogged, which requires expensive replacement (up to € 2,000).

1. Check the necessary type of additive

Before any intervention, check The exact type of additive Used by the vehicle (EOLYS, Finallyum, Adblue, etc.). This information is available:
✔ in Vehicle manual
✔ ON The additive tank label
✔ Consulting a mechanic or merchant

2. Fill the FAP additive tank

🔹 Material required:
✔ FAP additive compatible with your car
✔ Diagnostic OBD tool (to restore the notice)
✔ protection (gloves, glasses)

✔ Steps to follow:
1️⃣ Identify the additive tank (often under the car, near the fuel tank)
2️⃣ Unscrew the filling cap
3️⃣ Slowly pour the additive Until the required level
4️⃣ Close and clean the area

🚨 Attention : Some vehicles require a passage in garage Carrying out this because access to the tank is difficult.

3. Restore the vehicle computer

After filling, the notice message «Weak FAP fat» It can persist. A Restore through an OBD diagnostic suitcase It is often necessary.

✔ If you have a OBD toolFollow these steps:
1️⃣ Connect the OBD tool to the diagnostic socket
2️⃣ Select the form FAP / additive
3️⃣ Restore the additive level
4️⃣ Check that the warning disappeared from the dashboard

📌 Without Bique OBDa passage in garage or merchant It is mandatory to restore the notice.

What happens if the message persists after filing?

If the notice «Weak FAP fat» Remains displayed despite the filling, several problems can be the cause:

🔹 Defective level sensor : To be replaced
🔹 Non -reset calculator : Check with an OBD suitcase
🔹 Loss in the additive circuit : Check the pipes and joints

🚗 In these cases, a visit to a mechanic is recommended.

FAQ: answers to common questions

How do I know if my fap additive is low?
The dashboard displays the message «Weak FAP fat»Sometimes accompanied by a light of the engine.

Can I drive with a low additive level?
🚨 Yes, but not long! An absence of additive will damage your FAP and activate a degraded engine mode.

How much fills the FAP additive?
✔ Additive price : From 30 to 100 € depending on the model
✔ Garage workforce : From 50 to 150 €
✔ Total cost in the garage : From 80 to 250 €

Can we fill the FAP additive yourself?
Yes, but some models require A passage in the garage for access to the tank and the restoration of the system.

What is the difference between additive AdBlue and Fap?
🔹 Adblue It is used on diesel engines Euro 6 To reduce nitrogen oxide emissions (NOX).
🔹 The additive Fap it is specific for engines Diesel with particles filter To facilitate regeneration.

Conclusion: What to do in the case of a low FAP additive level?

🔹 Do not do it : A lack of additive can cause a FAP clogging and expensive repairs.
🔹 If the message persists after filling, a diagnosis is recommended in the garage.

📌 Last advice: Check your additive level Every 80,000 to 120,000 km To avoid any error connected to FAP. 🚗