After quite a bit of research, I've decided I needed to create my first post before I end up potentially throwing more money at parts (more importantly, money that could be going to fun stuff).
Here is the issue I am having. After buying my first 996 (or Porsche of any kind) about one year ago, about 6 months in, both the Oil Failure Indicator light came on (the one on the digital display and the solid red one with just a pic of the oil can). Needless to say, I freaked out, pulled over (luckily I was right next to a gas station), checked the oil and was about half a quart low. I topped off, and drove home since the pressure gauge on the dash was still showing oil pressure. After researching, I decided to buy an oil pressure sending unit and replace. I just recently got around to doing it because the car was on a lift for like 3 months to replace the entire suspension and brakes (yes, that's a long time, but I took my time and only worked on it about 2 days a month plus cleaning 20 years of road dust and dirt added alot of extra time). Anyway, after installing the new sensor, the oil lights are still on AND now the dash gauge is not working, just sits at 0. I have tried the following:

• Disconnecting the sensor altogether as I read that it should make the gauge top out (it doesn't move)
• I tested the ohms on both the old and new units 10.2 and 9.8 respectively
• Manually connected an oil gauge just to be sure I am actually getting pressure, I am (5 bars at start up).
• Tested continuity on both units, they appear to be "naturally on" circuits and creating pressure with air on my bench does not break the circuit. So I think this may prove they are bad?

Is there anything else I should test before just ordering another sending unit? Is there a way to test the dash gauge to make sure that is not the issue?

Thanks for reading this far and for any advice!

 

The oil pressure gauge will go off scale, past 5 bar, if you disconnect the sender (1 wire will do). Try this to see if the gauge moves at all.

 

That's the first thing I tried. Nada on the gauge.

 

Ok. I missed your note on that. The gauge could be bad or there is an open circuit in the wiring somewhere. I don't know the wiring layout so I can't be specific about where to look.

 

Sensor has 0-184 Ohms resistance acc to https://vdo-webshop.nl/en/pressure-s...590690838.html

Get yourself a potentiometer that goes up to 200 Ohms (or higher but less than 1kOhm) and connect its middle terminal to the wire that carries the signal of the sender to the gauge and one of the outer terminals of the potentiometer to (engine) ground. Turn the potentiometer fully into the direction of the outer terminal you connected to ground (the resistance between both terminals is then close to zero).
Check if the oil pressure warning light is on. If yes, then change the connection to your potentiometer over to the other wire that goes from sensor to the gauge.
Turn the potentiometers **** away from the outer terminal you've connected to ground (thereby increasing the resistance between both terminals). Your gauge should move up the scale towards 5 bar.
If it doesn't, either the wiring (probable) to the gauge or the gauge instrument itself (less probable) are broken.
If the gauge responds to turning the potentiometers ****, the sender(s) are broken.
HTH.

To test the wiring to the gauge find (using wiring diagram) the appropriate terminal for the oil pressure signal in the 2 big, round connectors in the engine bay and connect the middle terminal of the potentiometer to this. Observe as above. If the gauge now reads correctly, the signal wire is broken between sender and connector.
Testing the gauge itself requires removing the gauge cluster and find the appropriate terminal at the back of the cluster as well as finding a way to supply it with 12V.
Possible but I'd do the tests above first.

 

Thanks for the info, this is what I was looking for. I'll try this out and see what I find.

 

Why is the sensor the same unit that was in the air cooled engines? I had the same scare with the Oil Failure Indicator light 3 times and my Druck pressure pegged at 5 at times. Now the Druck is a little below 2 at idle sometimes as well. I know my sensor is going, just wished they had a better updated unit for all the electronics in the 996

 

Because the dash gauges were contracted to VDO, the same ones who have been doing Porsche gauges since the beginning....lol

 

So one dumb question in regards to this - the wire that carries the signal of the sender to the gauge

I assume that this wire is referring to the one that connects to the larger pin on the sender, which I think is the blue/white wire?

 

I see gn/wt carrying the pressure switch signal and gn/re carrying the pressure (potentiometer) signal from sensor to the large, 25 terminals, grey connector (terminal 17 and 16 respectively) in the engine bay on the RHS.
Source: Bentley manual

 

While driving a few days ago, I got a ECU message "oil pressure signal" or something like that.

The gauge was at zero (with the engine at 3000rpm), but no red light.

I did a DC-8 Flight Engineer move and tapped on the gauge with my knuckle.

The indicator immediately went back to 3 bar.

Obviously it is a connection issue inside the gauge...

Paul

 

Wanted to give an update on this. I was able to test per Hardtailer's suggestion. The potentiometer worked like a charm and told me that the oil light and gauge are both working fine. The oil pressure sending unit is, in fact, DOA out of the box. The good thing is that now I am an expert on replacing the sending unit, can do it in 10 min flat. 😉

Thanks again hardtailer for the help. Love this community.

 

Glad you found the culprit and thanks for reporting your findings!