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Old 31-10-18, 17:19
BruceB BruceB is offline
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T4 Post Icon MAF wiring and faults

Having read through the technical article I have found that I have no 12v supply at my MAF on my 2.5 TDI. The loom seems to run donw the front of the engine but before I pull the tray and the front of the car apart to find out where it goes (20 as a connection number is noted on the drawings I have, what is this?) Can anybody point me to where to find the other end of the cabling coming from the MAF plug?
If I ring it out and there are broken cables I'll rewire but it would be nice to trace the location first. Is there a plug or connection that I can ring out the cabling to the MAF plug from first, and if so where is it?
Any pointers appreciated, its just too cold, wet and dark to be mucking around outside without some sort of plan!
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Old 01-11-18, 17:53
JonCa JonCa is offline
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Default Re: MAF wiring and faults

Would imagine it's back to the ecu via the cable loom that runs across the top of the engine. It's frequently said that wires in this area of the loom suffer from insulation breakdown and consequent shorting with adjacent wires. May be worth breaking open to see.
Be good to give year and vehicle as basic info can be different

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Old 01-11-18, 19:23
BruceB BruceB is offline
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Default Re: MAF wiring and faults

Its a 2001 2.5TDI 102hp van, was auto but now manual.
The loom seems to go down the front of the engine and there is limited daylight during the week up here now so hard to work on the van, particularly underneath.
I am hoping to find the other end of the loom that goes to the MAF and ring it out rather than having to remove undertrays etc to trace it somewhere which I could possibly access without doing all this, and lying on the ground in the dark wet
If I ring it out and there are shorts/breaks then I will happily take it all apart to fix it, I just don't want to srtip half the van and then find out there is nothing wrong with the wiring out the MAF in the first place!
The drawings I have just say the supply comes from connection "20" but no clue of where this is, any help interpreting or finding this point very appreciated, I am hoping to spend a few hours sat looking for the fault.
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Old 01-11-18, 20:16
JonCa JonCa is offline
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Default Re: MAF wiring and faults

Have a look at this thread.
VW Books has a selection of wiring diagrams that may help you
https://www.vwt4forum.co.uk/showthread.php?t=224128

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Old 03-11-18, 19:21
BruceB BruceB is offline
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Default Re: MAF wiring and faults

I have looked through these and they are not particularly helpful, the wiring diagrams do not give very good detail on where in the van the various connectors are and only really say the connection for the 12v supply comes from "20" , unfortunately not particularly helpful if I do not not know where in the van this is without physically tracing the cabling.
I may have to start stripping the underside and front of the van down to fin this wiring route but this is not easy at this time of year up here, its basically dark and wet all the time and I can't get the van in the workshop as its too tall.
A pointer on where connection 20 is would be extremely helpful, if its inside the van or somewhere reachable I can prove the woring is broken or not without stripping, at least if I can prove breaks it would be so bad stripping down the van to get in and repair it. It would be really annoying to find the engine wiring is fine and its just a dirty or loose plug connection inside the van at the fuse box or similar!
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Old 03-11-18, 23:45
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Manxdog Manxdog is offline
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Default Re: MAF wiring and faults

Just fixed a similar problem on mine, as most people will say here, check wiring harness that is in conduit running across engine especially where it turns 90Ē at gearbox end, itís easy to spot if the problem is there, had to repair 4 wires on mine when it packed in after topping water up.
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Old 03-11-18, 23:52
T4 tiler T4 tiler is offline
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Default Re: MAF wiring and faults

I've also noticed some chafing of the loom cover on my 2.5tdi where it runs across the engine even though clipped in place, so I would definitely check every inch of it along there
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Old 04-11-18, 00:02
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Manxdog Manxdog is offline
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Default Re: MAF wiring and faults

Definitely worth checking. The wiring is loose inside the conduit and vibrates wearing through the wiring, then the damp gets on the copper and it gos green and furry!
Mine came to light after I spilt loads of water on it, run like and not rev, then when it dried out it was ok for a bit.
Unfortunately German wiring isnít as good as there Diesel engines, if you ever had to work on 50 series Deereís or any Bomag gear you would catch my drift!
Easy and cheap fix if thatís what it is, especially if people have been in it swapping gearboxís etc, donít take much to give wiring a bit of a tug if wiring a bit frail.
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Old 04-11-18, 01:58
mindriot mindriot is offline
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Default Re: MAF wiring and faults

The MAF wirong goes to the ECU, has to more or less, Continuity and IR tests will tell you whether theres insulation failure and core damage.
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