Oil Pressure Gauge - Again

[jbs911cab]

Just joining the 996 forum. Sold my 85 911 and moved up to an 03 996 cab - wow what a difference :jump::)

Anyway - am faced with the oil pressure gauge problem many have discussed before. My problem - oil pressure gauge went to zero just after getting the car (87K miles) (minor heart attack as I had visions of the engine grenading and a $20K bill in front of me). No oil pressure light. Went to this forum for some great advise - figured out how to replace the oil pressure sender without too much problem. Pressure gauge worked fine for a few days. On the way home from work it dropped close to zero again but fluctuated a little bit. Oil idiot light is off. Continued home and began diagnostics. With engine on (no oil pressure showing) - disconnect large wire connector from sensor and measure 12V between wire connector and ground. Ground the wire connector while engine is running and get oil can warning but no fluctuation in pressure gauge. Oil can warning goes away when I disconnect ground. With key on and engine off I get 12V to ground. When I ground the wire, there is no fluctuation in the gauge. I'm guessing a bad oil pressure gauge at this point but would appreciate any advise on next steps.

Thanks for any suggestions.

[Steve Tinker]

jbs911 - welcome to one of the best boards - there's heaps of really clever people here who no doubt will chime in.

It sounds like you may have a faulty sender unit, you can always get the unit replaced under warranty, BUT, the only sure way to see correct oil pressure is to temporarily connect up a mechanical pressure gauge to where the original sender unit fits.

At least you will know for sure that you have good oil pressure without reverting to guessing......

When you fit the mech gauge, the engine doesn't need to be hot - as a rough rule of thumb, oil pressure at idle with cold oil is about the same pressure as hot oil @ 3000 rpm.

Keep us informed of the outcome.

Edited September 8, 2010 by Steve Tinker

[jbs911cab]

Replaced the sensor already - that's what got the gauge working for a couple of days. Doubt the new unit failed so quickly. So now looking for the next step.

[rb101]

I doubt your oil pressure is actually dropping to 0. Were the connectors clean and free from corrosion?

[jbs911cab]

The actual oil pressure is definitely not dropping to zero or the idiot light would come on. I don't have a circuit diagram of the pressure sensor but I assume it has one circuit for the idiot light that is an on/off switch connected to the small connector. When there is pressure, the switch is open turning off the light. The other circuit is a variable resistance circuit that varies with oil pressure and is connected to the pressure gauge. With engine running (cold) the pressure is initially very high with the cold, thick oil (usually 5 bars on the pressure gauge), therefore the resistance to ground should be high (or could it be the reverse??? hmmm - need to go measure). Anyway, since I have 12 volts at the large wire connector, I'm assuming that I don't have a wire, connector or corrosion problem (this is a CA car). That leaves the variable resistance sensor circuit in the pressure sensor or the pressure gauge. Will go measure the resistance across the pressure sensor tonight and see what it tells me.

Does anyone have a circuit diagram of the pressure sensor circuit????

Thanks for any help.

[Loren]

It is a simple circuit.

The Green/Red wire goes from the switch to B5 on the instrument cluster.

The Green/White wire goes from the switch to A13 on the instrument cluster.

That is all there is -- so either the sensor is bad (or the chassis/engine ground is loose - but I would think you would see other problems with that) or the wiring is damaged or the cluster connector(s) are loose (not seated) or worst case the cluster is bad.

[jbs911cab]

Thanks for the feedback. I will check the pressure sensor again to see if I got a bad one. If the problem turns out to be the pressure gauge, can it be replaced separately or does the entire gauge cluster need to be replaced?

[Loren]

Unless someone like Palo Alto Speedometer can repair it - you would need a new cluster.

[bosstucker]

Sorry to resurrect a dead thread but a very similar thing happened to me yesterday. Right after start up and backing up the hill out of my driveway, heard the beep and saw the idiot light turn on and saw oil pressure gauge read 0 bar. 1 second later it was back up around 3.5-4 bar. Since it was so brief I decided to just go anyway and didn't have any problems the rest of the day though the car never sat around long enough to cool all the way. It happened twice over the weekend too but other than those three times it's never happened. Any ideas as to what is happening to make that the light turn on and the gauge drop to 0 then come back up a second later? My car is an '02 C4S.

Edited August 3, 2011 by bosstucker

[Loren]

Sorry to resurrect a dead thread but a very similar thing happened to me yesterday. Right after start up and backing up the hill out of my driveway, heard the beep and saw the idiot light turn on and saw oil pressure gauge read 0 bar. 1 second later it was back up around 3.5-4 bar. Since it was so brief I decided to just go anyway and didn't have any problems the rest of the day though the car never sat around long enough to cool all the way. It happened twice over the weekend too but other than those three times it's never happened. Any ideas as to what is happening to make that the light turn on and the gauge drop to 0 then come back up a second later? My car is an '02 C4S.

If everything else n the cluster is working - then start by checking the oil pressure sender.

[Samm]

Sorry to resurrect a dead thread but a very similar thing happened to me yesterday. Right after start up and backing up the hill out of my driveway, heard the beep and saw the idiot light turn on and saw oil pressure gauge read 0 bar. 1 second later it was back up around 3.5-4 bar. Since it was so brief I decided to just go anyway and didn't have any problems the rest of the day though the car never sat around long enough to cool all the way. It happened twice over the weekend too but other than those three times it's never happened. Any ideas as to what is happening to make that the light turn on and the gauge drop to 0 then come back up a second later? My car is an '02 C4S.

I had to replace the oil pressure sender last year on my 02 TT too because of the same symptoms you had just mentioned. In my case, the frequency of the sender failure had increased over time. I am no expert here but would suggest to check the following before having the actual sender replaced:

1) check if the 2 electrical connections on the sender are tight and secured; and

2) check if your battery is in good condition (I suspected that my not so good battery had damaged the sender).

If both of the electrical connections and battery are good, I am afraid that you may have to replace the sender. Good luck.

[bosstucker]

Thanks Loren and Samm, I will definitely check it out this weekend! I love this forum!