There I was, happily poodling through Bracknell heading for the M4 when I got a loud bong from the dash and big red
STOP! message followed by the oil pressure light. Luckily I could pull over almost immediately. Just as my hand was on the key to switch off, everything returned to normal. I had checked the oil level before I started out and I could see there were no puddles under the van. I suspected a faulty oil pressure switch rather than the oil pressure actually being low but without physically putting a gauge on it there is no way of being certain.
I had my VCDS lead and laptop with me so I connected it up. Oddly there is no mention of oil pressure in the engine controller but the instruments controller records it live as it does other dash warning lights.
The oil pressure switch is only a single wire sensor and only capable of reporting ok or not ok depending on the minimum pressure VW has set. It showed as not ok below 1500 rpm but ok above. But of course VCDS can only report what the sensor tells it and if the sensor is faulty it will report rubbish.
I drove very carefully on and it would occasionally do the same thing except that the dash messages varied. I always got the 'STOP' message but also got
OIL PRESSURE and
WORKSHOP MANUAL. In the few seconds when the warnings were up on the dash I listened to the engine for any slight harshness (I've heard a few oil-starved engines over the years) but there was nothing that worried me. So today I replaced the oil pressure switch and all is well.
I was much relieved to see the VCDS screen now showing 'Oil pressure ok'.
I wouldn't advise anyone else to take the calculated the risk I did. If you see any warnings on the dash to do with oil pressure (as opposed to oil level) switch off asap and get it checked. Because if you really do have low oil pressure you can do huge engine damage in a short time.
The oil pressure switch is down below the oil filter and you can't get to it without dismantling. The manual says to take the bumper and front panel off followed by the A/C compressor but I discovered you can do it easily in about an hour by another means. I'll post it up on the modifications board later.