How to: Clean the Mass Air Flow Sensor on a Mercedes M112/M113 Engine

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A mass air flow sensor (MAF) determines the volume of air entering the engine so the ECU can work out how much fuel is needed for an efficient detonation.

On the majority of cars the MAF just a little way down the air intake pipe from the air filter. The air does have to pass through the filter to get to the MAF so generally speaking they don’t get that dirty.

However if the MAF does get dirty it can lead to running issues such as rough idle, running rich and your check engine light may come on.

My Mercedes C240 has been running on the richer side of late and only just got through it’s last MOT for idle emissions. I doubt that the MAF is the issue but it’s super easy to get to on the M112 V6 and M113 V8 and preventative maintenance is always a good thing.

As you’re facing the engine, the MAF is on the left hand side cylinder bank by the little cut away on the engine cover.

MAF complete

The first thing you’ll want to do is take off the air box cover. The air box is the large plastic box towards the front of the car ahead of the MAF.

airbox complete

There are six metal clips that hold it in place. Three you will see instantly. Two towards the outer wing and one towards the headlight.

airbox clips 1

There are two more facing the block of the engine.

airbox clips 2

Finally there’s a longer clip at the back of the air box.

airbox clips 3

Lift the cover up. to expose the air filter. The air box cover will still be attached to the MAF’s pipe via two more metal clips. One at the top:

clip airbox to intake top

And one underneath:

clip airbox to intake bottom

With those undone the air box cover should simply pull away exposing the front of the MAF.

MAF front

At the far side of the MAF pipe you’ll see a jubilee clip holding the MAF to the rest of the intake pipework. Undo that with a flat head screw driver and pull the MAF forward.

All that will be holding the MAF in place now is a little electrical connector. To release that press the two tabs on either side of the connector and slide it back.

connector tabs

The MAF will now be free! Although there really shouldn’t be any dirt getting to the connection inside the MAF, you might as well check the condition whilst you are there. The inside of the MAF end of the pug should have five copper tabs:

MAF plug

And the plug should have five holes for them to go into!

engine plug

This is what the inside of the MAF looks like. This is called a ‘hot wire’ MAF. A constant current is passed through that metal wire. As the wire gets hot the resistance within it increases. By theory as cold air passes over that hot wire the temperature drops and resistance decreases. The more resistance there is the more fuel the ECU will want to put into the combustion chamber, so any dirt or dust on that wire can cause a running rich issue as less cold air will be getting to it.

MAF inside

To clean the wire, use a proper MAF cleaner available from Amazon here: Archoil AR2810 Mass Air Flow Sensor Cleaner – 300ml Aerosol

Or a good electrical contact cleaner designed to dry without leaving a residue such as WD40 Fast Drying Contact Cleaner 250ml

Once you’ve sprayed the MAF, leave it off of the car to dry for about half an hour. That way there won’t be any residue to throw any codes when you start the car.

Installation is simply the reversal of removal! Nice and easy and will hopefully keep your car running at it’s best!

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By Richard Francis

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