Buzzer of Doom- False warning???

[Blakefruid]

Afternoon all,
So I had a new head fitted to my 1.6 TD JX about 2000 miles ago and all has been very good till today when the buzzer of doom and flashing red light occured. I have a brickwerks oil front mounted cooler and vdo pressure and temp gauges. At cold start up the pressure is 4.5 bar, the idle pressure is just over 1 bar and a warmed up (80) pressure at 2500rpm is a smidge over 3 bar, this is totally normal. I have grey and blue pressure sensors that were new when the head was replaced, all wiring looks good and connectors are clean or new,
I've changed the oil (15 40 mineral) and Mann oil filter and I've now disconnected the external oil cooler. 
Still the buzzer is on at 2,200 rpm.
Any ideas what to check would be great...was thinking maybe the oil pick up could be blocking up, but no evidence of anything in the oil when I changed it.
thanks ever so much,
Blakie

[Aidan]

if you earth the high pressure switch feed from the engine does the bod sound at 2000+rpm - if it does then you have a wiring/ bod circuit fault, if it don't you may have a faulty switch - not everything new works, easy enough to test

where is the oil pressure gauge sender, is it shared with the high pressure sender, is that split well earthed ? as the switch for the bod needs a good earth - when I added a gauge on the scooby installation we had to add an earth as the t piece on a flexi hose was clipped to the manifold with an insulated p clip, the gauge sender was a 2 wire so worked fine, but I had false bod warning - the flexi hose to the t piece didn't provide continuity to earth

[Blakefruid]

Thanks for the help Aidan. So did the earth test for the high pressure switch feed and the bod sounded. So it must be the wiring or maybe the bod itself?? shall I just run a temporary wire from the engine to binnacle to eliminate the actual wire? or is there something better to do? thanks ever so much,
Blakie

[Aidan]

you could remove the bod circuit board since you have a gauge and you know the op is okay, you won't get the lamp on ignition that goes out when it starts and you won't get the lamp on as it seizes (which it won't as the gauge is reading all good) as removing the bod circuit removes the low pressure signal chain as well.
you could putting an earth on the high pressure line at the dash, if that doesn't work I'd suspect the dash pod or bod circuit.
I have a couple of bod boards including one diesel one I think but no way of testing it as I don't have a diesel

[syncroandy]

My notes on this topic are below, hopefully they'll help you check your system and sort it out.

VW DOPS function on pre-97 VW's:

The dynamic oil pressure monitoring system gets inputs from two pressure switches.

One switch is closed with no oil pressure and opens when oil pressure rises to about 0.3 bar. (Black/Blue wire)

The other switch is open with no oil pressure and closes when oil pressure rises to about 0.9 bar. (Yellow wire)

The monitoring system seems to only "look at" the .3 (.25) bar switch below 2000 RPM and ignore the .9 bar switch. Above 2000 RPM the active switch is the .9 bar switch while the .3 bar switch is ignored.

A. Ignition ON, engine NOT running -- or -- engine running at LESS than 2000RPM (.9 bar switch is ignored)

1. Low oil pressure exists (below .3 bar), keeping .3 bar switch closed
 --Oil light: Flashes
 --Buzzer: Silent

2. Normal oil pressure exists (above .3 bar), opening .3 bar switch
 --Oil light: Off
 --Buzzer: Silent

B. Engine running at MORE than 2000RPM (.3 bar switch is ignored)

1. Low oil pressure exists (below .9 bar), keeping .9 bar switch open
 --Oil light: Flashes
 --Buzzer: Sounds

2. Normal oil pressure exists (above .9 bar), closing .9 bar switch
 --Oil light: Off
 --Buzzer: Silent