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Discussion Starter · #1 ·
First off, this isn't an urgent low oil pressure problem. I just couldn't come up with a thread name that didn't made it seem like an immediate emergency.

The oil pressure light on my 1999 9-3 pops on with the in "on" before cranking, as it should. It then goes out after starting the engine. However, then after restarting the car, the oil pressure light does not pop on with the other dummy lights when they are being tested. If the car cools down sufficiently, the light will again cycle on/off when I turn it on.

It has never illuminated while driving, but I'm not so sure that it would in every case, so perhaps I'm just lucky so far.

What do you think the likely culprit is? I guess I can pretty much rule out the dash light, since it works sometimes. The oil pressure sending unit, I suppose, but in my experiences sending units are either all or nothing -- they work all the time or not at all. Any ideas on how to test?

Thanks,
mryan
 

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Mine was doing exactly the same thing, but has now failed completely. I don't get the oil light when you switch on the ignition. You can test the sender unit by pulling the wire of the back (you can reach from the top of the engine, under the throttle body) and touching it to the block with the ignition on. The lamp on the dash will light.
 

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Much prefer the oil pressure gauge, and an oil temperature read out as well......but in a "low priced" car...

As I read it, I think nothing is wrong; residual oil pressure will keep the lite "off" for a short time . Every time the key is turned "on", a bulb ckeck is enacted...
 

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Discussion Starter · #4 ·
The bulb check isn't happening every time the key is turned though. Well, it is, but the oil pressure light isn't illuminating.

My first thought was that residual pressure kept the light from turning on at the bulb check, but it should still through the light at the bulb check I reckon.

I never noticed this before, as I usually turn my car on in the morning, drive to work, and drive home. Since it has 8-12 hours to rest, it always cooled all the way down, and in that case the light always works. at the bulb test.
 

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I had the same symptoms as you and I tested the circuit exactly as batko describes. It gradually got worse until I changed out the sending unit, and now it functions properly. It was an easy and cheap fix; about $15 for the sender and maybe 15 minutes work to change it.
 

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I cheated a bit in removing mine. The oil filler tube is right in the way, so it is impossible to get a socket on the sender without removing the tube. I noted that a 15/16" wrench was the correct size, but there was not room to swing one. So, I hacksawed off about 6" of a 15/16" box wrench, slipped that over the sender, and broke it loose. The aftermarket replacement was a bit smaller, so I had a correct crowfoot wrench to fit it for tightening.

Before anyone admonishes me for destroying tools, hear me out. Most of my hand tools are Snap-On and are treated with the respect that they deserve due to their cost. However, I always keep on hand some spare wrenches from a lower-cost supplier like Craftsman or Matco just for occasions like this. I have many times cut, heated and bent, welded, or otherwise modified tools for specific purposes, and then kept those very same "specials" for the next time I encountered a similar need. There are plenty of off-the-shelf "specials" from Snap-On, Kent-Moore, etc., but nothing beats making your own tool for a specific job when you need it. These inexpensive "beater" tools are, after all, tools; they exist to get the job done, not to be wall hangers. Besides, in this case, I happened to have two Craftsman 15/16" -1" double-end box wrenches, so losing one didn't represent much of a sacrifice.
 

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dabrig said:
So, I hacksawed off about 6" of a 15/16" box wrench, slipped that over the sender, and broke it loose...
That is a good tip. That location is very awkward on the NG900.
 

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Discussion Starter · #9 ·
On second thought, seeing the pressure sender is easy. Me being able to get it off where I live (only street parking) with my tools (not many, as I live in an apartment without garage) is going to be a beast of a challenge.

dabrig -- I see you are a metro Detroiter, and you have the tools. Perhaps I could slip you some $$$ to do the job for me? I do not want to have to go to the dealer, where I was quoted some $250. Or if there is anyone else is NW Ohio/SE Michigan who could do the job.

The GP Sorensen switch -- part OPS53 -- was $4.94 auto Advance Auto Parts. But I don't think I'll be able to get the install done. I assume that the aftermarket at Advance is intended for multiple makes/models, as I didn't think they would stock the switch for a 99 9-3.

mryan
 

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I think you are suggesting that the oil pressure switch is failing to open when the engine and the sender are hot.

If I understood that correctly, try this before you tear into this in the cold, and w/o a garage:

First let the car sit long enough to make sure the engine is really cold (takes a few hours).

Make sure the oil light indicator lights up with ignition on and engine off.

Then, start and run the engine just long enough to get the oil pressure up, at idle. Like, 30 seconds, until the oil light goes off. Shut the engine off. Remove the key from the ignition long enough for the lock to pop out.

Now turn the ignition on again w/o starting the car, with engine still cold, and look for the oil light. 50/50 chance it will not come on, even with a cold engine... :cheesy:
 

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Discussion Starter · #11 ·
PMI said:
Now turn the ignition on again w/o starting the car, with engine still cold, and look for the oil light. 50/50 chance it will not come on, even with a cold engine... :cheesy:
OK. I got to my office two hours ago, so I can't check yet, but I will when I leave tonight.

Maybe I was too verbose earlier. I will explain in brief:

After warmup (even running the car for one mile or so) the oil pressure light doesn't go on when the other dummy lights go through their check phase when I restart the car. The only time I see the oil pressure dummy is when I leave home and leave work, after the car sits for hours.

So, even with a cold engine, why is there only a 50/50 chance that the light will come on? Shouldn't the light always come on with ignition on w/o starting the car? My previous cars always cycled the oil pressure light on in the systems/dummy light check.

mryan
 

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Discussion Starter · #12 ·
Left the office. After the car sat for about 8 hours, no oil light at any point. Will see if it lights in the morning. It would seem strange for light and pressure sending unit to fail at the same time, but we will see. I will ground the wire to test bulb if there is no luck with the tomorrow morning.
 

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There is no "systems" check for the oil indicator.

It is wired directly to the oil pressure sensor on the engine block. The sensor is actually a simple switch. It closes when there is no oil pressure, the light comes on, and that's it. Connecting the wire to chassis has the same effect as a closed switch due to no oil pressure.

The switch operates at an extremely low pressure, much lower than normal oil pressure, even at idle.

The light will often not come on on a restart, especially in winter.
 

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mryan55 said:
On second thought, seeing the pressure sender is easy. Me being able to get it off where I live (only street parking) with my tools (not many, as I live in an apartment without garage) is going to be a beast of a challenge.

dabrig -- I see you are a metro Detroiter, and you have the tools. Perhaps I could slip you some $$$ to do the job for me? I do not want to have to go to the dealer, where I was quoted some $250. Or if there is anyone else is NW Ohio/SE Michigan who could do the job.

The GP Sorensen switch -- part OPS53 -- was $4.94 auto Advance Auto Parts. But I don't think I'll be able to get the install done. I assume that the aftermarket at Advance is intended for multiple makes/models, as I didn't think they would stock the switch for a 99 9-3.

mryan
Sent you a PM.
 

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mryan55 said:
Left the office. After the car sat for about 8 hours, no oil light at any point***. Will see if it lights in the morning. It would seem strange for light and pressure sending unit to fail at the same time, but we will see. I will ground the wire to test bulb if there is no luck with the tomorrow morning.
***There is then something wrong.
Residual oil pressure looses its effect over a short time...I have never measured this.
Use Batko's method to test the switch and lite(its the same as mine and a million other mechanics)..
Oil pressure switches are at 99.99...% reliability; but they can leak ( or used to)..
 

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Discussion Starter · #16 ·
Went to try again this afternoon after sitting for 13 hours. Light did not come on with key in on position w/o starting the car.

How can I access the wire on the oil pressure sender from the top of the motor? I am not the most nimble, and I can't seem to see the wire. I suppose I should double check the light before I change the pressure sender.

Although I am hoping it is the sending unit. I trust myself to the mechanical stuff, but I don't mess with auto interiors, so it would off to a garage to get the bulb changed if need be.

mr
 

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mryan55 said:
How can I access the wire on the oil pressure sender from the top of the motor?
Depends on which engine you have.

B204 engine only:

The sensor is behind the plastic oil filler tube, about an inch below where the two parts of the filler tube are joined. You can reach it from the passenger side, if you follow the filler tube with your fingers. (NOT the metal stay which supports the intake manifold, but the plastic filler tube which is closer to the engine block.)



To test it, you do not have to disconnect the wire, which can be a bit hard to fit back on the lug. You can use a test lead with an alligator clip, and attach it to the metal single wire connector at the sensor.

Oil Pressure Sensor test

Don't wear your favorite shirt... :cheesy: , that area traps a lot of dirt.
 

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earthworm said:
A hydraulic lift would be nice, that and a heated garage with a 12' ceiling.:cheesy:
As soon as you get one, I'll bring my car right over right away... <chuckle>
 

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I had what I though was a pretty good visual on the sender by just removing the plastic cover on the intake. You can look down between the intake runners and see the wire going right to the sender and also see most of the sender. That's ready access in my book, compared to some of the nightmarish accessibility on some vehicles. By comparison, I have to pull the intake manifold off of my daughter's Saturn V-6 in order to change the thermostat.
 
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