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Literally, white van man
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Discussion Starter #1 (Edited)
:confused: Hopefully someone can help, dont know if this should be here or in the Electrical section.

How does the MAF sensor work (a very basic description will do)

I would like to understand how it works so I can decide if I can use a sonic bath I have access to. The MAF isnt oily but it has a slight 'dusting' of fine black deposits (possibly soot/deisel/carbon deposits) that have got through the filter.

I was thinking I would submerge the sensor part of the MAF into the sonic bath and give it a blast to clean it, then dry the whole unit before refitting.

The Question is, will I trolly some internal gubbins if I do this?

The MAF was identified as 'reading' slightly low by VAGCOM at full throttle (possibly reading 700 when 950 ish was expected? but I could be confused ;) )

Any help would be appreciated T:

Chris
 

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Literally, white van man
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Discussion Starter #2
:) Ok, after a Wiki search, it appears that it may be a 'hot wire' MAF sensor, A control wire to detect ambient temperature and a hot wire to detect airflow (the hot wire is cooled by the airflow and resistance changes with the temperature at a known rate, or something :confused: ) These signals are sent to the ECU and in conjunction with other sensors the fueling is adjusted accordingly.
The sensor can deteriorate over time and give different readings from those expected, not necessarily showing up on the fault code reader as it is still reading, just not at the correct values, this error can be caused by 'contamination' on the wires changing the 'heat' dissipating qualities (and, hence, the resistance readings to the ECU)

Soooo, in theory, if I only submege the wires and the inside of the the airflow opening, leaving the electrical connections out of the cleaner, it 'should' clean up nicely ;)

If i get the chance I'll do it next week, and post the results.

The MAF IS reading low at the moment, and I have had limp mode issues intermittantly, so I have nothing to lose and in worst case I'll have to get a new MAF from VW, best case is it cleans up and I have no further problems T:

Chris
 

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Chris

Sorry to hear your having problems. You van prob had a fit now that the pump timing is right.;)

MAF normally wont give you limp home mode - but can give you reduced power that feels like it might be limp home.

Are you getting a flashing coil on the dash when it happens?

PS. Ive cleaned tonnes of MAFs and never got any better readings from them. best way to tell is disconnect it and drive it round see if you get reduced power still.

Or - I'm in yeovil U-Drive on monday - you could come find me :D

Laters

Jez:ILU:
 

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Literally, white van man
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Discussion Starter #4
T:Cheers for the response Jez,
:(No, I have no dash indications at all, If I feel like it is in 'limp' mode and I turn the ignition off then start it again it seems to clear, the feeling is like a lack of 'boost' when it reaches about 1800 rpm, more rev's but no 'boost'.
As you said the MAF was reading low I thought I'd try to clean it (it will cost me nothing but a packet of hobnobs ;) ) If no joy, then a new MAF and see what happens, after that come and see you again for the VAGCOM and see what sensors are iffy (or loom wires?) After that I'm out of ideas.
it's more of an inconvienience at the mo, I can see it getting right on my T*"s if it continues LOL:
The Van is so smooth now after the DMF/clutch etc, just this little issue to get over (then the next, and the next..........LOL:LOL: will it ever end, probably not)

Chris
 

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if you disconnect it it will revert to factory settings, if it shows improve ment at that stage then it needs replacing by a proper vw part. the Vac system is all linked so a test will show a fault on any of the system but will not define it that much to say its the MAF sensor,I wouldnt bother cleaning it, its highly unlikly it will make any difference. trying this or a good one is the only true way of testing it seperate from the rest of the VAC system.( what i have found) hope this helpsT:
 

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Literally, white van man
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Discussion Starter #6
:) Ok, a bit of an update,
I'm fitting a new VW MAF sensor in the morning because when it was checked on VAGCOM it was reading low, I managed to borrow a SEALEY code reader/reset 'box' and it came up with the following codes

17569 -163 KWP1281 1/3 (I 'Think' this decodes as MANIFOLD TEMP SENSOR CIRCUIT OPEN-B+)

17563 -163 KWP1281 2/3 (MANIFOLD ABSOLUTE PRESSURE SHORT TO B+)

17965 -163 KWP1281 3/3 (CHARGE PRESSURE CONTROLLER POS DEVIATION)


I reset all the codes and checked the memory was clear, first time it was, started the engine and went for a drive, it felt like it went into 'Limp' mode. Stopped and checked the codes and all of the above was present again, I cleared them again and started the engine then stopped it and checked again, only the last code was present :(

I unshipped the 'sensor' that dips into the inlet pipe leading to the EGR elbow after the turbo, and cleaned that with contact cleaner/degreaser (it was slightly oily) the connector to the multiplug looks to be clean.

I repeated the test above with the same results.


Sooo, WTF does all this mean :confused: Is this indicating something wrong with the vaccume sensor/s and if so what does it look like so I can hit it with something LOL:

In all seriousness, if anybody has any helpful info I would be most appreciative T:

Chris (scratching his head in a WTF type way LOL:LOL:LOL: )
 

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last code is overboost.

Check pipes from n75 to wastegate on the turbo. Make sure the wastegate actuator is not siezed.
 

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Literally, white van man
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Discussion Starter #8
:confused: Another update

The ordered MAF didn't arrive. will be here Tuesday

I replaced the Pressure,temp sensor on the inlet manifold inlet pipe, rest all the codes, went for a drive and......

...Now in limp mode all the time, with the same first two codes :(

I unplugged the MAF and went for another drive, No discernable difference :confused: and on checking the codes I had the first two and 17552 (MAF open circuit short with ground) I cleared this code and still have the first two present :(

I am Changing the MAF on Tuesday and will read the codes again.

In the garages 'BIG BOOK OF CODES' for the ones I have, it rather alarmingley mentions 'wiring' alot, so am I looking at an auto electritian having fun with my looms? (Jez ;) )

More on Tuesday perhaps

Chris
 

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Map sensor and Temp Sensor are the same unit.

I would guess ignition live or the earth wiring to the sensor is damaged somewhere.

As mentioned before the MAF wont give you limp home ever just general sluggishness.
 

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Literally, white van man
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Discussion Starter #10
Map sensor and Temp Sensor are the same unit.

I would guess ignition live or the earth wiring to the sensor is damaged somewhere.

As mentioned before the MAF wont give you limp home ever just general sluggishness.
Cheers Jez,

The 'sensor' on the inlet manifold obviously does both pressure and temp then T:

I can see it's going to have to be a professional that sorts out the wiring issues :( Are there any simple checks I can do as an electrical biffer, gently part the conduit that feeds the multiplug to the sensor I suppose, are the wire colours standard? what colour should I be looking for? Is there a common earth and where is it?
so many questions and so little knowledge on my part LOL:LOL:

How long do you think it would take a professional to sort it out? (I know, how long is a piece of wire), what I mean is, is it quite straight forwards to someone who knows what they are doing? ie, these places feed the sensor, it will take me about 2 hours to check all the possible places there could be a fault?

just so i can get the most info, here is the fault so far

intermittant limp mode (well, reduction in boost) If i turned the ignition off and then on, it would reset mostly.

I unplugged the multiplugs to the MAF and the MAP sensors (one has silicone grease 'cage mod' the other is clean)

I put the code reader on and got the following codes 17563 and 17569 (once I got 17965) then cleared them, started the van and rechecked codes, mostly the first two came back.

I changed the MAP sensor (pressure and temp?) on the inlet manifold feed pipe

Drove the van and it is in limp mode all the time.

Unplugged the MAF and drove the van, it felt exactly the same, plugged in the MAF again and the van is still in limp mode.

Checked the codes again and got the first two and 17552 (I cleared them and only the first two returned) Checked the codes on a snap-on checker, slightly more info and the 'big book of codes' pointed to the sensor or 'wiring'


Pooh! :(

Any advice appreciated.

Jez you say you are in Yeovil on Monday, Is your day filled already? LOL:

Chris
 

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Looking at a diagram all four of the wires go back to the ecu but Temp and Map are wired seperately which is odd because you have two codes.

You can pick back the loom and inspect or pin test them back to the ecu. Maybe not a job for the faint hearted.

If you wanna have a go then

Brown and Red - 52
Brown and white - 73
Red and Green - 31
Blue and Black - 71

I'll be at U-Drive by the football club on Monday give us a ring and come over and we can have a quick look.

I'm still thinking overboost. Have you checked your wastegate?
 

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Literally, white van man
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Discussion Starter #12
:) I 'think' the wastegate is ok (the rod from the flying saucer to the lever on the turbo) it has quite a strong spring pressure that I have to move against towards the back of the van through about 20 degrees (movement of the rod of 10-15mm)
As for me checking the ecu and pins and wires, I think my limit is reached before that, If i can get away from work at lunchtime I'll pop accross, if you can have a quick look that would be excellent, nice quick sort for you and a few more quid in the bank (in my dreams perhaps)

Either way, if it's ok with you I'll give you a ring tomorrow T:

Cheers

Chris
 

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Literally, white van man
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Discussion Starter #14
T::DT: WooHoo!
Jez (ZMOK) had a quick look at lunchtime, checked on VAGCOM with the new and old MAP sensors fitted, one had both codes, one had a single code, I wiggled the wires in the loom and both codes popped up. Jez stripped back the loom cover and discovered.....A broken wire! Get in!
He repaired the wire cleared the codes, and I took it for a drive.

WooHoo! (again :D )

Sorted

(he also showed me the wiring diagram, for all the sense it made to me LOL: , But when we applied the symptoms to the discovered fault it made sense T: )

Jez, you sir.......are a steely eyed missileman.

Thank you very much.

Chris
 

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Congratulations mate. Its nice to read that some people do actually sort there problems out.

Whereabouts was the broken wire exactly? Am tempted to strip all mine and check them.
 

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HI there i to have limp mode on my ex AA done all vac pipes and still same. I have 17964 negative boost got new new 75 on but will try it out tuesda, which wire are where was it . Thanks
 

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From the Boost sensor on the intake pipe follow wiring down 8 inches by the header tank- Brown and Red snapped in half underneath insulation tape.

Check all your intake pipes for the negative boost code.
 

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i havre had hesitation at 1800 revs and lots of black smoke cleaned very dirty egr no better unplugged maf ran good no smoke but down on power new allard delete pipe runs like a new bus
 
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