TDi lambda code - EFI - 121 Mass air flow (MAF)

[Ade B]

Had this code recently on my 145k 850 TDi, and replaced the entire MAF assembly from my other 307k scrap car. This instantly cleared the code and removed a huge flat spot.

Two weeks later and the car is driving fine, but the code returns!
Still perhaps a slight flat spot, but nothing as bad as the previous set up, so doubting that the replacement MAF is so knackered it would throw a code.... Or could it?

Any ideas as to reasons why this code would come up again with a different MAF?

[Ade B]

Any ideas?

[doingitsideways]

Hmm... Maybe best to send Martin Smith a PM, Ade. Maybe he'll get an email notification then.
He really knows his onions with these.

Only think I can think of is maybe reset the ecu and see what it does.
Also, maybe your replacement is still slightly worn on the tracks with it being an old skool swinging arm/track type MAF.

I think if the ecu receives a couple of bad readings from the MAF it stores a code.
Could be wrong though.

[martin_r_smith]

If thats a full copy of vol fcr have a look at the live readings and see what it says at idle, desired vs actual etc.

Most likely though a second bad maf. Very simple to open up and put the arm onto a new track though, did it to mine and a few others now and its working fine for me still after 3+ years.

[Ade B]

Originally Posted by martin_r_smith

If thats a full copy of vol fcr have a look at the live readings and see what it says at idle, desired vs actual etc.

Most likely though a second bad maf. Very simple to open up and put the arm onto a new track though, did it to mine and a few others now and its working fine for me still after 3+ years.

My version of Vol FCR seems to be quite simple. Will read and delete codes, but no in depth areas for timing or anything like that. (if anyone would like to donate a copy let me know!).

So put the arm on a new track? Hmmm, not quote sure what will be needed to be done there. Saw the metal door type arrangement inside the inlet tract, guessing that's the culprit?

[doingitsideways]

Carefully open up the black plastic lid, very sharp knife job.

Inside you'll see three tracks on a PCB, and an arm with three corresponding contacts.

Over time, the tracks on the board wear out, so it's possible to very carefully bend the arm so the contacts run on a fresh bit of track.

No pics from when I did mine, but it's simple enough

[Ade B]

Originally Posted by doingitsideways

Carefully open up the black plastic lid, very sharp knife job.

Inside you'll see three tracks on a PCB, and an arm with three corresponding contacts.

Over time, the tracks on the board wear out, so it's possible to very carefully bend the arm so the contacts run on a fresh bit of track.

No pics from when I did mine, but it's simple enough

Interesting! Will need to investigate that!

[doingitsideways]

Originally Posted by Ade B

Interesting! Will need to investigate that!

Even a moron like me can figure it out Ade, I'm sure you'll be fine!

Will make perfect sense when you get the lid off.
Just be careful, Bosch didn't want mere mortals getting them open!

[Ade B]

Ok, so my MAF has got dismally bad lately! Will need to try and move the track....

So to open the MAF all I basically do is prise off the black plastic top?
Nothing to dismantle? Plug area or anything?

Is it a case of silicone sealing it shut afterwards?

[martin_r_smith]

Best guide I found https://youtu.be/-11J8XawQtc