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Discussion Starter #1 (Edited)
Morning All,
I'm not a huge poster on the forum so forgive the long winded post. Its pent up frustration lol

I have a 1998 VW T4 1.9TB (ABL) and have the dreaded Oil pressure light / buzzer issues which is driving me nuts.

I have checked and changed the pressure sensors, both high & low. To what Heritage parts centre suggested were the right ones for the ABL engine, Blue for the low pressure sensor and white for the high pressure sensor. All seemed well for a while then the occasionally the noise from hell started again, but only what appeared to be randomly.
So another search of the Internet resulted in finding an excellent write up by Penbryn. So I decided to replace the wiring from the alternator and the high pressure sensor upto the fusebox. I found a few cracks so it was worthwhile but to my utter dismay, the familiar sound was there again but only occasionally again.

Then I checked the pressure switches and the Instrument cluster to ensure they were working as expected. Using the trusty voltmeter I can confirm that once above 2000rpm the high pressure sensor changes state and looks stable, albeit the vehicle is stationary. Also the instrument cluster appears to indicate correctly if I ground the high pressure signal and rev the engine above 2000rpm.

So next was a change to the voltage regulator in the alternator, just in case the quality of the signal was degraded, but no, its still there.

So further frustrated Internet searching has led me to a number of other options / questions, this is where I need some guidance / feedback
  • I believe at the last service the van was filled with 05W 40 oil, however I’ve seen on several threads that people with higher mileage vans change that to 10W 40, mines done 210,000 miles.
  • Some people have experienced issues when changing to a certain type of oil filter.
  • A failing oil pump can cause drop in pressure leading to the DOP system triggering
  • As the issue only ever happens when driving I am wondering if it could be oil “slopping” around in the sump, would a baffle plate help with this.
  • As the “w” signal is in effect a Pulse width modulated signal which the instrument cluster uses to determine RPM, could the alternator still be an issue even though I’ve changed the voltage regulator?
I still think this is an electrical issue and the one area I haven’t attempted to touch yet is the loom between the fuse box and the instrument cluster.

Sorry this is a long winded post but that damn buzzer is driving me nuts. I’m at the point where I may just disconnect it and use a pressure gauge and instrument to monitor the pressure.
 

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Have you actually checked the oil pressure .Gauges are not very expensive .Could be oil pressure is in fact marginal at times .For reference a good oil pressure at tick over is 2bar and rising To 4 bar at 2000 rpm .
 

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Discussion Starter #3 (Edited)
Have you actually checked the oil pressure .Gauges are not very expensive .Could be oil pressure is in fact marginal at times .For reference a good oil pressure at tick over is 2bar and rising To 4 bar at 2000 rpm .
Good Spot, the actual pressure is something I've not yet checked. thanks for the quick reply, pressure gauge ordered 👍
 

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That oil pressure was on my van 160,000 mile and the reading was with cold oil .Would be a bit lower with hot oil .Maybe a heavier oil required .These vans predate widespread use of lighter viscosity synthetics after all .
 

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Discussion Starter #5 (Edited)
So once the engine was warm the tick-over pressure was 2 bar and at approx 2000 rpm the gauge was showing 3.6 bar. The pressure appeared pretty stable. I also checked the pressure switch which was actually the grey one so its got a switching pressure of 0.9 bar.

So from what I'm seeing, at least stuck on the drive, the engine looks ok for 209,000 miles and with the a 0.9 bar switch it look like purely on numbers I'm ok. So why is the damn thing so random?

I did even try jiggling the wires around between the fusebox and the cluster but nothing, stable as you like.

So I think the next step is to rule out any actual pressure drops causing there issue by fooling the instrument cluster into seeing constant pressure above 0.9 bar. So as its a normally open switch, if memory serves me correct, I need to earth the yellow wire.

This should tell me whether its an electrical fault or not

any feedback on my approach is greatly received as auto electrics is not my thing. Give me a big Aircraft any day
 

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Oil pressure is good in fact ,and that is what matters Dont think any actual fall in pressure is causing the warning to work .Must be some electrical gremlin .This good oil pressure indicates that the engine is actually in good shape .
 

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Discussion Starter #7
todays episode, My brain hurts

So I've earthed the yellow high pressure cable to earth and left the pressure switch floating. I've now been out for a good long drive (essential journey) and nothing. Quiet as a mouse. In my simple head this tells me its either a signal quality issue from the sensor or its actually momentary loss of pressure. But the engine feels good and thanks to bournricha I now know the pressure is good.

I'd love to see the electrical schematic for the DOP electrics as I would assume it has some form of passive filtering to "smooth" out any electrical noise and maybe a timer to check whether its actually a pressure drop or not. Or am I over thinking this?

That damn buzzer just resonants in my ears. It's not my tinnitus, I hope
 

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Is this what you need;

 

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Discussion Starter #9
Is this what you need;

Thanks for the link, that was actually the first thread I read and now I'm at the point where I might just start again and check through the instructions again(y)
 

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From your 1st post (yeah, I DO read everything!), changing the brushes/regulator pack on the alternator will NOT affect the wiring for the "W" terminal.
That is taken straight from one of the coils.
Bad connection/faulty wire will stop the dash getting the correct signal.
May or may not be your problem, but unless you have a meter than cam measure the frequency of the signal from the W terminal, you can't rule that out.
 

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Discussion Starter #11
So today’s update. I went back to square one and checked everything again.

1. Disconnect the wire to the high pressure sensor on the filter housing and let it float (un-connected).
2. The oil buzzer should now come on and indicator will flash when the van engine speed is above 2000 RPM.

checked and confirmed this is happening

3. Now connect the yellow wire to ground and rev the engine past 2000 RPM… the buzzer should not sound at all.
checked and confirmed this is happening.

So I’ve checked the sensor itself again. Using a voltmeter I connected one end to the sensor and one end to the positive on the battery. At tickover I have 0v and once I get to 2000 rpm the voltage increases to 14v and looks stable. So I believe the sensor is ok.

this fault only occurs when driving and it appears so random. The only thing I haven’t been able to do is check the quality of the ’w’ signal from the alternator. I do know it had fuel leak on it from the throttle spindle. Not sure if that is noteworthy.

so do I bite the bullet and try a new alternator or give up and ground the sensor wire
 

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I wouldn't go down the new alternator route.
People who "recon/refurb" them use a tank of diesel or paraffin to actually CLEAN them. (I've done over 100 alternators/starter motors/DYNAMOS!)
The "W" wire is a direct connection to one of the windings, so no amount of oil/crud would interfere with that. (Apart from the external connection/wire.)
If the alternator is charging, that means the windings must be OK.

Have you checked ALL the wires in the loom that runs at the back of the engine on RHD vans.....a VERY common problem (that doesn't happen on LHD :) )
 

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Discussion Starter #13
I wouldn't go down the new alternator route.
People who "recon/refurb" them use a tank of diesel or paraffin to actually CLEAN them. (I've done over 100 alternators/starter motors/DYNAMOS!)
The "W" wire is a direct connection to one of the windings, so no amount of oil/crud would interfere with that. (Apart from the external connection/wire.)
If the alternator is charging, that means the windings must be OK.

Have you checked ALL the wires in the loom that runs at the back of the engine on RHD vans.....a VERY common problem (that doesn't happen on LHD :) )
Thanks for the info. It’s set my mind at rest on the alternator. As of the the wires, I’ve checked the continuity on the the wires associated with the DOP system up to the fuse box. I replaced red, blue and yellow wires. I may try replacing the low pressure sensor wire next even though continuity was good.
it just seems weird that once the yellow wire is grounded no matter how long or varied the drive, silence
 

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Discussion Starter #14
well I'm not counting my chickens yet, but I think I may have fixed it. Even though the continuity on the low pressure sensor was good I decided to change it anyway. Then I went for a good long drive, motorway and A roads. Nothing.........

So, I'll give it a few more days before I start to get smug face but thanks for listening to my tales of woe
 

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I went through the same grief with mine, it's only done 22,000 miles on a new motor, I bought both my sensors from a well known vw supplier who confirmed they were right, and after all the time I wasted replacing wires, i read about dodgy sensors so bought two new ones direct from vw(cost around £45) and not had the buzzer of doom since replaced last year.

Sent from my I3312 using Tapatalk
 

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Could be you had continuity but too much resistance .Encountered this problem the other day with the thermo switch on a gas fire .Yes there was continuity according to the multimeter but the tiny voltage from the thermocouple could not get through to keep the gas valve open .Presumably because of corrosion of the switch contacts .New switch and all good .So continuity can be a bit misleading when dealing with signal strenght currents .
 

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Standard multimeters, on Ohms range, use VERY little current so as not to damage any components.
If you have a symbol with a diode on it, use that as it will use higher current to get over the "barrier" that a semiconductor has.
It's (unfortunately) the difference between a 5 quid cheapy, and a £100-200 Fluke meter (of which I have 3!)
I can even measure starter currents up to 1000 amps.
 
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