2002 C5 2.0HDI low oil pressure ?

[2cvandy]

Hi,
I've looked through old posts and whilst I've found similar problems, I've not found a solution.
It's not urgent, and I'd be pleasantly surprised if I get an exact diagnosis and cure, because it's an odd one, but I'd be interested in your thoughts.

The car's a 2002 C5 break, 2.0HDI with 216,000 miles recorded.
The problem started a year ago, but I thought it was cured.
I'd recently done an oil / filter change when the message "oil pressure insufficient" flashed up on the display.
The car was running fine and sounded fine, so I carried on home.
Once home, I found a (very) slight oil leak from the oil pressure switch, so I replaced that and the message never reappeared, until now.
We are now a year (and 12,000 miles) on, I've just done another oil / filter change, and the "oil pressure insufficient" message is back.

At first, I thought it must be connected with the fact that the oil has just been changed, but I always use a good quality filter and always fill the filter with oil before fitting.
Then I noticed that the message is only flashing up when braking to a stop downhill, so I though maybe the fault lies with the oil level sensor rather than pressure ? I confess, I'm not sure if that's possible ? Wouldn't the message read "low oil level" if that was the case ?
The message hadn't shown for a couple of weeks, but then yesterday morning it was back. But then I realised something else, it was -6 deg yesterday, and I've only been getting this message when the engine is cold, once the oil temp gauge gets above the blue section it stops happening. I can't remember if this only happened in cold temps last time, but it was winter.

Thoughts ?

[2cvandy]

Ok, this is going to get annoying now, the " low oil pressure " warning is popping up regularly, seemingly at random.
That in itself wouldn't be so annoying if it weren't for the " beep beep beep " that accompanies it.
The car's been running fine for long enough with this fault for me to be sure that the oil pressure is actually fine, and the pressure switch has already been replaced.
I'm going to have a crawl under this morning and look if I can actually see the oil level / temp sender to change that too.
But at £80 or so, I'm reluctant to buy one unless I know that's the fault.
So, questions are ;-
can the sensor be tested ?
will cleaning it help ?
and can I leave it disconnected ? or do I need a resistance across the wires to fool it ? and if so, what resistance ?

anybody know ?

[RichardW]

Might be worth wiring a lamp in parallel with the oil pressure switch so you can see if it's staying made - at least that will rule it out. I'd be more inclined to think it was a wiring fault, or a problem with the underbonnet fuse box.

[2cvandy]

or a problem with the underbonnet fuse box.

You could be on to something there.
Cleaned everything up in the under bonnet fuse box, cleaned the multi-pin connectors.
No annoying warnings for two days now,,,,,,,,,,,,, fingers crossed.