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How to: Engine air filter change w204.025 350cdi

When I went through the service papers of my car a few days ago, I noticed that only at 80´000 km a change of the engine filter was noted in the digital service booklet. With meanwhile over 190´000 km it is again so far.

Annoyingly, the 350cdi exists in the w204 assembly from 2011 in two different versions (with plate filter or cartridge filter) and my car was produced in the transition month of February when the change took place. I was offered the wrong filter in all online shops. Only the direct search for the part number, which I could read in the engine compartment, gave me the right filters as hits.

In my case there are two cartridge filters with the part numbers:

A6420942404 passenger side

-A6420942304 driver’s side

These two filters are also available as a set under the part number:

A6420940000

The tools

You only need two Torx screwdrivers as a tool for the changeover.

Torx T25

Torx T30

and about 10 minutes time.

The exchange

  • Engine hood open
  • Pull the motor cover upwards (this is clipped in at 4 points).
  • Find the two filters
  • Loosen the retaining clamps on the passenger filter and loosen the two Torx screws, making sure that the screws do not fall off.
  • Now you can slightly push away the intake duct on the engine side and then pull out the filter catcher upwards/outwards. Make sure that no dirt enters the intake duct on the engine side.
  • Reinsert the new filter and carefully tighten the screws and close the clamps. Make sure that the red seal on the engine side is not jammed or twisted.
  • The change is similar on the driver’s side. The only difference is that a pressure sensor is still installed in the filter cartridge. Here one must unscrew the sensor before with the Torx T25 and pull it out carefully. Put the new filter back in and screw the sensor back on.
  • When everything sits perfectly again at the end, you can reinstall the engine cover and look forward to new filters.

Watch your step! After replacing the filters, Mercedes plans to reset the adaptation values of the HFM (hot film air quantity meter) with the Star Diagnosis. This is probably due to the fact that the engine control can get confused with the sudden change of the air transmission rate. Resetting the adaptation values informs the control unit of the air filter change and can prevent the engine control lamp from lighting up.

I didn’t reset the HFM value. ¯\_(ツ)_/¯

With my w209 CLK I also ignored this hint and had no problems with it. Let’s hope for the best.

After a short test drive I can tell that small speed fluctuations disappeared when driving with cruise control on the country road. I had been able to observe this phenomenon for about four months. If this simple solution could help, I am more than satisfied.

Wie immer: Keine Garantie auf die Richtigkeit meiner Tätigkeiten. Jeder ist selbst für seine Sicherheit und sein Handeln bei der Arbeit an Fahrzeugen verantwortlich.

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