oil, and both brake lights on = bad oil pressure sensor? (3.2 Carrera)

[Bob Prosser]

(3.2 Carrera daily driver)

Hey all. Real quick: at start-up this morning, I see the oil, emergency brake, and brake pad sensor idiot lights are all on. Everything was fine yesterday when I shut her off.

The car runs fine: oil levels, pressure, etc., are all good. I suspect the oil pressure sensor (replaced once at 90K miles). Tell me if you think it's something else. I can find no fuse that would seem to be the culprit. Brake pads are new.

I want to double-check with you guys -- if I remember correctly, if the oil pressure sensor on top of the engine goes bad, all three lights will illuminate ... am I right or wrong?

Thanks for your input.

[dshepp806]

I haven't heard that one but will take a look at the schematics...

Sounds like the unit these signals run through may have failed?

Let's take a look..........

[dshepp806]

...looking...

[dshepp806]

I'll be damned ! never ever noticed that additional input,..if I did, it was long ago and presently forgotten.....

The unit that drives the parking/pad/belt indicators go through the mentioned control unit and drive their grounds indicator lights does take the two brake pad sensor feeds into pins 1 and 2. The E-sensor signal comes in on pin 4. And, low and behold, we have the oil pressure (idiot signal? I think not) LAMP signal coming in at pin 7. Looks like ground calls the shots....wiring? grounds?

I'll have to look for the schematics for the "inners" of this solid state ) (IIRC) relay switch to see if they have a nifty go-about inside....now that I think about it,..it must should you want to read a "coded" message up on the dash. The signal from the pressure switch heads straight to the GAUGE bulb and tells you then and THERE something's up...but I have to agree that this same signal is picked off of the lamp pin (GRN/WHT) and sent to the control unit (what for but to give you 3 lights up on the console?) Seems redundant but possible.

Hell, I'd simply disconnect the oil pressure switch (assuming your contention, it would send a ground if failed?). Your removal of this signal going to the unit, and seeing what the lights do would put that to bed? As far as these lights go......

Interesting footnote you've presented,.....

Still looking for that schematic..........then I'll know for sure...

Bet someone (who knows 4 sure) will chime real shortly...watch.



I

[dshepp806]

also has the input for the brake fluid level switch at pin 4 (paralleled with parking brake contact...

just checked the owner's manual and it makes no mention of indications telling you that a component is bad.

[Bob Prosser]

Thanks for all the noodling on this.

Tomorrow I will see if I can find a way to pull the wire on top of the pressure sensor.

If all the lights go out, then that'll give you some feedback eh?

[Bob Prosser]

Hey all. I came across a thread that speaks of the same general problem, i.e., if the oil pressure sensor/switch goes bad, the oil AND brake idiot lights come on. Click here: Brake and oil light

Thing is, the car being discussed is an '83 SC, and mine is an '88 Carrera. I realize there are some differences between the two models when it comes to the brake system (brake switches are different -- SC is mechanical, and Carrera is hydraulic), but when it comes to the oil pressure idiot light I think they are the same?

Looks like this is the part, though I'd rather have OEM if it's this much work to replace. I mean do you REALLY need to do a partial engine drop?!

[dshepp806]

No need to partial drop for the swap on my 89. Just have to remove some topside stuff. I think 83 would be quite different.

Still haven't found all of my prints (schematics) on this box.

So, the 3 light that are on (post 1) are the pad wear warning light (dash), the E-brake light (dash) and the oil sensor idiot light (your words) on the gauge.....[NOT the oil light]////

right?

[86 911 Targa]

Originally Posted by Bob Prosser

(3.2 Carrera daily driver)

Hey all. Real quick: at start-up this morning, I see the oil, emergency brake, and brake pad sensor idiot lights are all on. Everything was fine yesterday when I shut her off.

The car runs fine: oil levels, pressure, etc., are all good. I suspect the oil pressure sensor (replaced once at 90K miles). Tell me if you think it's something else. I can find no fuse that would seem to be the culprit. Brake pads are new.

I want to double-check with you guys -- if I remember correctly, if the oil pressure sensor on top of the engine goes bad, all three lights will illuminate ... am I right or wrong?

Thanks for your input.

I think that dshepp806 is right on.

It has been a long time since having experienced the same anomaly on our '86,

and, without a Bentley, it took me a while to resolve this problem!

However, upon replacing the pressure sender, the issue was resolved.

The oil pressure sendor sends a ground to both the oil pressure lamp,
AND and the combination indicators.

Remove the (Green/White) wire from the oil pressure sender and ground it.

If that resolves your issue, replace the oil pressure sender.

By the way, on the 3.2, you will have to remove the air filter, air meter, and throttle assy.

So here are a few things you might want to check/replace:

1. The sound absorbing barrier which is appended to the back of the seats.

2. The crankcase breather gasket and hose.

3. The oil cooler thermostat O-ring.

4. And of course the oil pressure sender gasket.

Also, take care to re-install your throttle assy vaccum lines in their original connections.

I transposed two of ours and it took me a bit of time to find the problem.

Here is your schematic of interest.

Good luck,

Gerry

[86 911 Targa]

Originally Posted by Bob Prosser

(3.2 Carrera daily driver)

Hey all. Real quick: at start-up this morning, I see the oil, emergency brake, and brake pad sensor idiot lights are all on. Everything was fine yesterday when I shut her off.

The car runs fine: oil levels, pressure, etc., are all good. I suspect the oil pressure sensor (replaced once at 90K miles). Tell me if you think it's something else. I can find no fuse that would seem to be the culprit. Brake pads are new.

I want to double-check with you guys -- if I remember correctly, if the oil pressure sensor on top of the engine goes bad, all three lights will illuminate ... am I right or wrong?

Thanks for your input.

Here is the layout for the vaccum lines.




You may pm me.

Gerry

[dshepp806]

I was speaking of the schematic for LED PC card so that I can see how the signal drives out to the bulbs........I think it's odd that the user manual would not state such a thing......that green/white wire isn't paralleled off the actual oil pressure warning bulb for no reason.....

I'll find that print soon enough,..I have it somewhere deep within the bowels of data....

My Bentley doesn't go back to '83 to compare circuits.

Best of luck !!!!!!!!

[Bob Prosser]

Originally Posted by dshepp806

So, the 3 lights that are on (post 1) are the pad wear warning light (dash), the E-brake light (dash), and the oil sensor idiot light (your words) on the gauge.....[NOT the oil light] right?

Hmm ... well, yes ... as I wrote: "oil, emergency brake, and brake pad idiot lights are all on."

I've ID'd them here:



So yes -- three lights are on, and I doubt it can be a coincidence.

Thanks for the thoughts!

[86 911 Targa]

Originally Posted by Bob Prosser

Hmm ... well, yes ... as I wrote: "oil, emergency brake, and brake pad idiot lights are all on."

I've ID'd them here:



So yes -- three lights are on, and I doubt it can be a coincidence.

Thanks for the thoughts!

Ground the green/white wire at the sender, turn on the key, verify that all is well, replace the sender, and be done with it.

The PC board holds some solid state stuff which is not worth getting into.

Trust those of us who have performed this repair......

Good luck,

Gerry

[Bob Prosser]

Thanks Gerry. So, going by what you write (or did not write), it appears that this is a tight bit of work but I do NOT have to drop the engine partially to replace the sensor?

[86 911 Targa]

Originally Posted by dshepp806

I was speaking of the schematic for LED PC card so that I can see how the signal drives out to the bulbs........I think it's odd that the user manual would not state such a thing......that green/white wire isn't paralleled off the actual oil pressure warning bulb for no reason.....

I'll find that print soon enough,..I have it somewhere deep within the bowels of data....

My Bentley doesn't go back to '83 to compare circuits.

Best of luck !!!!!!!!

It would take a very detailed manual to define circuit analysis on the Porsche PC boards which are, as you well know, widely located on the 911's. (defogger, turn signal relays ect.).

Please advise if you have one, especially for the '86 rear window defogger relay.

I have a set of factory '86 911 manuals which, in all cases, shows a symbol (like a transistor) in a box on the electrical schematics, but no functional description as most techs would not get involved in troubleshooting solid state circuits, but would replace the part.

Here's an example....

[86 911 Targa]

Originally Posted by Bob Prosser

Thanks Gerry. So, going by what you write (or did not write), it appears that this is a tight bit of work but I do NOT have to drop the engine partially to replace the sensor?

That's right.

I've done it twice.

The last time it was about a 3 hour job.

But get a Bentley, and take your time.

Fender covers, upon removal of the throttle assy a rag over the intake manifold,
and all of the other good precautions.

You may pm me.

Good luck,

Gerry

[dshepp806]

Yes, I've a boatload of prints......

I think (for me anyway) it IS worth looking into the schematic elements to see how these signals are handled (the engineer in me?) I can tell what it's doing without super detailed prints by looking (simply) at components used...again, that's me (only).

As stated previously, you do not have to drop the engine for this simple replacement of the switch.

So, go ahead and change out that switch, bud.

Best,

Doyle

[Bob Prosser]

Thanks to all you guys for the input. Truly appreciated!

So, does anyone with experience on this subject know if this non-OEM replacement pressure switch that Pelican sells is worth it, or should I look to the dealer for original (assuming they have one)?

I mean, three hours+ to install a $5 part? I'd pay $50 if I knew it'll not go out again like those crappy brake light pressure switches -- the ones that bolt on to the master cylinder (I've changed more of those that I care to recall).

[86 911 Targa]

Originally Posted by Bob Prosser

Thanks to all you guys for the input. Truly appreciated!

So, does anyone with experience on this subject know if this non-OEM replacement pressure switch that Pelican sells is worth it, or should I look to the dealer for original (assuming they have one)?

I mean, three hours+ to install a $5 part? I'd pay $50 if I knew it'll not go out again like those crappy brake light pressure switches -- the ones that bolt on to the master cylinder (I've changed more of those that I care to recall).

Bob,

I've been back there twice. Once for a breather hose, and once for the "divine" pressure switch.

The sender I replaced at about 60K miles was the original which I think lasted about 10 years.

As per my previous post, there are a few other things you can do while you are "back" there,
think of it as a multi-function repair/preventive maintenance project.

And yes, buy a dealer part.

You have all of the data you need from the previous posts for this time consuming but simple project.

You may pm me.

Good luck,

Gerry

[dshepp806]

Updates on this "quick" fix?