Low Oil Pressure Light Came on after 19 Years on MK 2 Fiat Punto

I've got a Year 2000 Fiat Punto Sporting Mk2 16V 1.2 Petrol Car.
I've had this car since new and looked after it and never had a break down in 19 years. This car is used in London so I do very few mile son it each year, approx 2,000 miles a year as I main drive to the train station and use public transport. Maybe take it on the motorway once or twice a month at most.

The other week I got in my car to drive to the train station which is only about 5 minutes drive away and for the first time ever I noticed the Low Oil Pressure Light remained on. when I came home from the station it was still on. I've not driven the car since and it's parked at home on my driveway.

I check the oil levels very frequently and checked once again and it was 3/4 up the top of the dipstick, so there wasn't low oil.

In order to fix the problem I tried the following, none of which has worked so far.

I changed the oil (Castrol Magnetec 10W 40)
I change the Oil Filter (Mann Filter)
I changed the Oil Pressure Switch (which operates as normally closed circuit at rest)

After changing these 3 things the light still remains on.

I also tried testing the car with the wire that plugs into the oil pressure switch unplugged and the low oil pressure light remains on.

So I am thinking perhaps this is an electrical issue?

I did do a test with an electrical meter of the reading from the centre pin of the oil pressure switch lead (i.e. the wire that normally plugs into the back of the switch) to the car body and it read 17.2 when the meter was set to 200k. So not exactly a full on short but there is a reading there. Someone else who owns a similar car tested theirs and got a similar reading, so I think this is normal for the car?

Any ideas what to do next? Or what the cause might be?

I'm hoping to get hold of a mechanical oil pressure tester and use that to see what reading it gives, however the one I've ordered I saw just got two bad reviews on Amazon both people saying it didn't read anything when they tried it. However I ordered this particular unit because it was the only one with a gauge that goes up to 140 PSI, all the others read 0 to 500 PSI so they'd be very hard to see any small PSI readings.

For sure, if your engine had no oil pressure it would rattle like hell
The fact that there's no change when the pressure switch is disconnected sounds strange - as if there is something else on the same circuit that is registering.
The only way to be sure of oil pressure is to have a manual gauge connected.....40 psi hot would be about right. If the oil pressure bypass valve in the filter housing is stuck open you may see what you are getting here, of course.
John

Wiring fault or dash fault if it's the same with sender unplugged.

Measure the middle pin on the sender to ground with your multimeter while engine running for peace of mind (should be open circuit). To prove oil pressure is ok (which it will be).

With the sender unplugged the dash light should be off regardless of engine state.

Today I just thought of another way to test for oil pressure - I noticed on the new Oil Pressure Switch that I installed that is said 5 to 7 PSI on it - so it needs at least that much pressure to disconnect the circuit.

So then I thought why not install a meter across the switch and use that to see if the switch disconnects once the car is started - I managed to find an old lead that fitted nicely into the pin of the switch - video below shows that as soon as the car is started there was enough pressure to activate the switch and break the circuit (which would normally turn off the low oil pressure light inside the car).

I don't know how the engine sounds to anyone else, it sounds fairly normal to me - usually my car gets a lot quieter as soon as it's on the move. Also the car battery had been unplugged for at least a week so I assume the car's computer / ECU has lost all it's settings and is in a learning mode on this first start.

BTW when I added back the oil to the car, I put in 2.4 litres and it showed at full on the dip stick, after letting the car run for approx 2 minutes and then rest for an hour I rechecked the dipstick and it went from full to half way on the dipstick.

I believe the car uses 2.8 litre in total - The oil filter is brand new but had been run on a previous test over a week ago when the troubles first began after putting in the new oil so I assumed it was holding a certain amount of oil as well. So there's probably another 200 to 400 ml to go to get the oil to the new full mark.

Id say your car has a wiring loom fault - but whereabouts is anyones guess! Check out the plug connectors in that area.
You can hear the oil pressure building as the engine starts so I dont think there is an issue with that.
The psi value of the switch is indeed, when the presure drops and the light comes on.
John

I just managed to get the low oil light to turn off by plugging it back in the switch - it seems it's as if this system isn't as simple a ON and OFF even though that's how the switch works.

There was a small resistance in the wire that goes to the switch - so that resistance seems to tell the car the difference between being ON / OFF and Disconnected

Only thing I can think of why the light has gone off now and not the time I tested it after changing the oil, oil filter and oil pressure switch is that I disconnected the battery for over a week - so the car's computer has probably reset itself and lost old values.

I was thinking to myself it seems really unsafe to have a low oil pressure warning light that goes off when the wire is disconnected because if you got a cut in the wire by accident you'd never know, but by using a system of resistance it would be able to tell the differences between 3 states at least.

I got hold of a gauge from Amazon today but I think it's defective as the needle never moved, I'm not even sure if the oil is able to get through the tube and this same gauge has two 1 star reviews since the time it was ordered that said the same thing - it didn't work at all.

Interesting thing to note is that when I unplugged the wire to the Oil Pressure switch - this time it went off before I even started the engine.

So I think there is a mix of the light being something that gets stuck in the car's computer as always being on when there's no more fault and needs a computer reset, in my case probably caused by disconnecting the battery for a long time.

So, going back to post #6, is everything ok now or is the light still misbehaving?
John

Burnerman said:

So, going back to post #6, is everything ok now or is the light still misbehaving?
John

Click to expand...

It seems fine - no more warning light - it comes on when you first insert the key but as soon as the engine fires up it goes off instantly. Car seems to drive fine.

I think disconnecting the car's battery until the memory was wiped helped fix the problem - of course now the car has new oil, filter and a new low oil pressure switch

All back to normal - that's good to hear.
I can't say I've heard of a battery disconnection causing this, but every day's a school day!
John

My daughter used to have a 2006 Punto 1.2 (sometimes called the "Grande Punto"). I don't know if that is the same model as yours, but if it is, they suffer from a variety of electrical problems. First of all, check the main battery earth cable. It goes from the battery negative terminal to the chassis, but then carries on down to the gearbox. The connector to the chassis is crimped part way down the cable and water runs down the insulation and corrodes the copper conductor, leaving you with a poor earth to the body, but the earth to the engine is still good. That's a tricky fault to find. (It cost me a starter motor when there was nothing wrong with the original)!

Secondly (and it might be different on your model) the main fuse box is directly under the gap between the bonnet and the left hand front wing. That makes it hard to get the lid on and off properly. If you take it out, you might find water has entered the multiplug connectors on the bottom of it. That also causes electrical gremlins!

Avocet said:

My daughter used to have a 2006 Punto 1.2 (sometimes called the "Grande Punto"). I don't know if that is the same model as yours...

Click to expand...

No mine is the Mk 2 - which is totally different car to the Grande Punto - I think Grande model was made with GM

... Well I drove the car from London to Luton and back again - no issues .. car seems fine .. I did after disconnecting the battery follow the lead that gives an Earth between the car and battery and scrape away to give the best possible connection, although it seemed fine.