W166 air mass flow sensor (MAF) question

[MLHappy]

Hi all, please help! I have a 2015 ML350 (W166) which has the OM642 Diesel engine. Recently I had the engine management sign come on, and been advised my mechanic that the mass air flow sensor (MAF) is showing faults and needs replacing. Annoyingly I had a new Mercedes original MAF fitted in 2021, now they’re retailing at £1000+ new!

My options are either:

1. Have it replaced again with an original so £1000+ and then labour, so expensive
2. I’ve bought a MAF sensor cleaner spray and wonder if this is a part that I can even remove, and clean the sensors?
3 I could buy an used one from eBay, I’ve seen some based in Lithuania about 1/5th of price of a new one, but wary as to if they’d work
4. Fit an aftermarket one which are less than £200 on eBay, but concerned if they actually work or come up with faults on the dashboard.

Any advice greatly received! Thank you

 

[MarkE350]

Hi MLHappy, I feel your pain...

I have a post here on a similar MAF replacement: MAF assembly - how to undo the flexy connectors | Engine
This may be of use if yours is the same arrangement with the 2 MAF sensors connected to a central T piece with rubber flexys that then goes into the turbo.
A word of caution first, I saw on another forum that someone managed to break a MAF doing this so it is at your own risk and you need to take care!

Using a hot air gun I have managed to separate the 2 MAF sensors from the rubber flexys, I managed to source genuine Bosch replacement sensors for £120 each and also bought new airbox seals and turbo seal from Merc dealer (may as well change whilst doing this). Would also have replaced the air filters, but they were just done less than 2000 miles ago.

I am now at the point of trying to get the MAF sensors back on the rubber flexys and the plastic securing ring back on. 1st attempt was a failure as the rubber flexy hasn't quite seated correctly in one section, so today I am about to get the heat gun back out and have another go. As a last ditch contingency I might need to use some high temp silicon sealant but at the moment will have another couple of tries to see if I can get it all back together and properly seated/sealed. Will keep you posted.

 

[Supernoodle]

I would question the diagnosis. Chance of failing once is low, but twice? Unless they are getting oiled up up, which unless you resolve will continue to happen.
When it was replaced were the replace MAF/filter service routines run

 

[MLHappy]

Hi MLHappy, I feel your pain...

I have a post here on a similar MAF replacement: MAF assembly - how to undo the flexy connectors | Engine
This may be of use if yours is the same arrangement with the 2 MAF sensors connected to a central T piece with rubber flexys that then goes into the turbo.
A word of caution first, I saw on another forum that someone managed to break a MAF doing this so it is at your own risk and you need to take care!

Using a hot air gun I have managed to separate the 2 MAF sensors from the rubber flexys, I managed to source genuine Bosch replacement sensors for £120 each and also bought new airbox seals and turbo seal from Merc dealer (may as well change whilst doing this). Would also have replaced the air filters, but they were just done less than 2000 miles ago.

I am now at the point of trying to get the MAF sensors back on the rubber flexys and the plastic securing ring back on. 1st attempt was a failure as the rubber flexy hasn't quite seated correctly in one section, so today I am about to get the heat gun back out and have another go. As a last ditch contingency I might need to use some high temp silicon sealant but at the moment will have another couple of tries to see if I can get it all back together and properly seated/sealed. Will keep you posted.

Hi MarkE350, thanks so much for your detailed reply! I really appreciate it, and I enjoyed reading your journey so far (I also read your other post via the link you sent). I look forward to your updates to see if you managed to fit it all together, it’s such a shame that Merc didn’t design the parts to be replaced separately! I’ve attached some images of the part in my ML engine. Did you ever consider trying to find a used original part? I haven’t so far been able to find the correct numbered part (A6420901642).

Thanks!

 

[MLHappy]

I would question the diagnosis. Chance of failing once is low, but twice? Unless they are getting oiled up up, which unless you resolve will continue to happen.
When it was replaced were the replace MAF/filter service routines run

Hi Supernoodle, thanks for your reply. You raise a really good point and something I asked the mechanic, at the time in 2021 the part cost £450 approx but now it’s over £1000. He tells me that they can last a lifetime or the 60,000 miles or so that I’ve done since it’s been replaced. There is an engine management light on the dash and the car tends to jerk on acceleration so there’s definitely an issue. Do you think I should go to a different place to get another diagnostic reading perhaps?

Appreciate your thoughts, thank you.