2 oil pressure senders on aaz... which one is really needed?

[DonGTI]

I was looking at the AAZ on my car and an aaz on my friend's car... and I noticed that he has an oil pressure sender on both the oil filter housing as well as on the head...

i have an oil temperature sender on an adjacent spot on the filter housing and an Allen bolt where my friend's pressure sender is.  My oil pressure sender is on the Right side o the head looking from in front of the car. But he has that as well as a second one on the housing.

I checked the 1.6 NA i had on before, as well the 1.8 GTI engine and they both have 2 senders... My engine bay wiring has a single loose connector close to the oil pressure sender... same color as my friend's wire that hooks to the oil filter housing.  

Why are there 2?

And why is the oil light shut off like normal? even with one sender disconnected? Do the senders work differently?

If i had to keep just one should i leave just the one on the head or on the oil filter housing?

thanks
Daniel

[Black Smokin' Diesel]

The system is a dynamic thingymabob setup or something. Basically, one sensor triggers below 0.3bar on the head and one triggers at 1.4bar on the oil filter flange. If any of those sensor detects a drop in pressure below those thresholds, it will trigger the oil pressure light in the gauge cluster and you'll hear a buzzer.

If one of the sensor isn't connected, it could be that the sensor is bad or you have an oil pressure issue.

[Vincent Waldon]

In the stock config (dual sensor) the sensor on the head is normally closed and opens when it sees the correct oil pressure (0.25bar).  When it closes it turns on the light.

The sensor on the oil filter flange is normally open and closes when it sees the correct oil pressure (0.9/1.4/1.8 bar depending on engine type and if it's equipped with a turbo... your AAZ will likely be 0.9 bar).  The car only pays attention to this sensor over 2000 RPM and if it looks and the sensor is open both the light and the buzzer come on.  

So, when it starts to buzz because the car's oil pressure is on the edge when hot at 2000 rpm many people just bypass it by grounding the sensor's wire... this may be why you only have the one sensor.

This (finally) answers your original question... of the two sensors the key one is the low pressure sensor on the head because it's in use all the time. Having said that, people that bypass the high pressure sensor  sometimes live to regret it !!  ;-)

[DonGTI]

but my wire is not ground ... it is just hanging ildly... why doesn't it give any warnings if disconnected then?

[Vincent Waldon]

Does your oil pressure warning light come on when you turn the key to "on" ??

[DonGTI]

yes, that's the strange bit... it works normally! turn on the key to acc and the oil light starts blipping on and off, alternator stays on and oil temperature reads correctly.

when i start the engine the oil light goes off, as does the alternator  

Wiring wise its a 1988 Mk2 gti not gtd and has no RPM connection with the dash since i haven't had the time to play with the W terminal thing.

Dashboard does not have buzzer

[Vincent Waldon]

Wiring wise its a 1988 Mk2 gti not gtd and has no RPM connection with the dash since i haven't had the time to play with the W terminal thing.

Aha  

That's the answer... no tach signal, no way for the cluster to know you are past 2000 RPM and it's time to look at your sensor...er... loose wire... so no buzzer.

So you're fine... the system is watching the lo-pressure sensor at all times (and you know it's working 'cause the light comes on and then goes out when you start the engine) so you'll be alerted if something really bad happens to your oil pressure.

[DonGTI]

Thanks Vince