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Old 07-28-2012, 10:23 AM   #1
Frank-i-e
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Default Oil Light "on" but how?

Hey guys, so I just bought a 2005 STi and the oil like came on. The thing is, he has an AEM Oil pressure gauge and the OEM on is just there plugged in but not screwed into the block. The gauge reads pressure, and the oil level is appropriate. I just parked it back and stayed home hoping someone could share some knowledge and help me out. The light wasn't on for a little over a week since I have had it. So i don't believe it is cause by the OEM one hanging there but I did move it out of the way a few days ago to slightly hide it more.

Anyone have an idea as to why? I am not driving the car to be safe.

Thanks!
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Old 07-28-2012, 10:32 AM   #2
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When you moved the OEM sender to better hide the sender it is probably touching a ground point. Now that it is grounded the light on the dash is illuminating because its not seeing oil pressure. If you have a good working after market gauge I would take the old sender out completely, toss it in the tool box and tape off the one wire that goes to it.
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Old 07-28-2012, 12:45 PM   #3
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Quote:
Originally Posted by ToyotaMike View Post
When you moved the OEM sender to better hide the sender it is probably touching a ground point. Now that it is grounded the light on the dash is illuminating because its not seeing oil pressure. If you have a good working after market gauge I would take the old sender out completely, toss it in the tool box and tape off the one wire that goes to it.
That was it! Thank you SO MUCH! I was freaking out like no tomorrow.
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Old 07-28-2012, 02:54 PM   #4
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also pick up a killer bee pick up asap !

http://www.killerbmotorsport.com/ind...ickupStory.htm
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Old 07-28-2012, 08:50 PM   #5
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Originally Posted by Frank-i-e View Post
That was it! Thank you SO MUCH! I was freaking out like no tomorrow.
No problem, glad it was an easy fix
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Old 07-28-2012, 10:15 PM   #6
the suicidal eggroll
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The oil light is very dumb. Basically it works like this...

Positive voltage goes into one side of the light in the dash. The other side of the light goes to the one wire that plugs into the factory switch. The factory switch is as simple as can be. When pressure is above ~3 psi, the wire is isolated from the body of the switch. This leaves the light with an open circuit so it stays off. When pressure is below ~3 psi, the wire is connected to the body of the switch. If the switch is screwed into the engine block, the body is "ground", so when the pressure drops below 3 psi, the wire is connected to ground, which completes the circuit and turns the light on.

In your case, the switch was not hooked up to an oil galley, so it was always seeing 0 psi, so the wire was always connected to the body of the sensor. Where you had the sensor before, it must have been isolated from any other metal parts in the engine bay (the vast majority are connected to ground). When you moved it, it was now making contact with some piece of grounded metal, which completed the circuit and turned the oil light on. People can get similar results when they wash their engine bay...the water tends to "pool" around the switch, and can partially ground out the wire, causing the light in the dash to turn on (usually it's pretty dim though).

In your case, like ToyotaMike mentioned, just unplug the wire, wrap it in electrical tape and tuck it away somewhere, then do whatever you want with the switch itself.
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Old 07-28-2012, 11:38 PM   #7
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Quote:
Originally Posted by tekfoc
also pick up a killer bee pick up asap !

http://www.killerbmotorsport.com/ind...ickupStory.htm
Yup!!! U better check that!
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Old 07-29-2012, 01:16 PM   #8
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Yeah I see why appears to be non OEM oil pan sealant and frequent the forums so I wouldn't be surprised if he did that already. I'll make sure to ask him!

Thanks everyone for the help, and the explanation!
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Old 07-29-2012, 04:33 PM   #9
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Why people even disconnect the OEM unit is something I will never understand. You can leave it as is and use a different oil galley plug for the Aftermarket unit. Leaving parts to just dangle in the engine compartment is just ghetto looking, not to mention it causes problems like this!

Im guessing the old owner didnt know that you can just unplug it and take the sensor out and the light wont come on. This way you dont have problems like this. Or just re-install it for a backup as it was from the factory and put the aftermarket gauge sender at the rear galley plug. The more things to tell you something is wrong, the better IMO.
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Old 07-29-2012, 09:58 PM   #10
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The galley plug under the alternator (where the OEM switch is) is the preferred location for an oil pressure sensor.
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Old 07-30-2012, 01:06 AM   #11
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Originally Posted by xluben View Post
The galley plug under the alternator (where the OEM switch is) is the preferred location for an oil pressure sensor.
its fine in the rear galley, hundreds of people put it there and it makes Zero difference. It would have prevented this... or just taking out of the car would have also.
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Old 08-06-2012, 11:21 PM   #12
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Quote:
Originally Posted by UK-Wagon View Post
Why people even disconnect the OEM unit is something I will never understand. You can leave it as is and use a different oil galley plug for the Aftermarket unit. Leaving parts to just dangle in the engine compartment is just ghetto looking, not to mention it causes problems like this!

Im guessing the old owner didnt know that you can just unplug it and take the sensor out and the light wont come on. This way you dont have problems like this. Or just re-install it for a backup as it was from the factory and put the aftermarket gauge sender at the rear galley plug. The more things to tell you something is wrong, the better IMO.
I like this idea as well.

Where is rear oil galley plug?
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Old 08-06-2012, 11:45 PM   #13
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The oil light is useless. Once it comes on, you more than likely already touched down a bearing and the shortblock is done. If you actually had lost pressure, you would already know.

Glad your motor is ok and the oil light coming on was the result of another persons laziness
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Old 12-03-2012, 05:06 PM   #14
wagonsarewinners
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Quote:
Originally Posted by the suicidal eggroll View Post
The oil light is very dumb. Basically it works like this...

Positive voltage goes into one side of the light in the dash. The other side of the light goes to the one wire that plugs into the factory switch. The factory switch is as simple as can be. When pressure is above ~3 psi, the wire is isolated from the body of the switch. This leaves the light with an open circuit so it stays off. When pressure is below ~3 psi, the wire is connected to the body of the switch. If the switch is screwed into the engine block, the body is "ground", so when the pressure drops below 3 psi, the wire is connected to ground, which completes the circuit and turns the light on.

In your case, the switch was not hooked up to an oil galley, so it was always seeing 0 psi, so the wire was always connected to the body of the sensor. Where you had the sensor before, it must have been isolated from any other metal parts in the engine bay (the vast majority are connected to ground). When you moved it, it was now making contact with some piece of grounded metal, which completed the circuit and turned the oil light on. People can get similar results when they wash their engine bay...the water tends to "pool" around the switch, and can partially ground out the wire, causing the light in the dash to turn on (usually it's pretty dim though).

In your case, like ToyotaMike mentioned, just unplug the wire, wrap it in electrical tape and tuck it away somewhere, then do whatever you want with the switch itself.
So are you saying that a factory switch installed as such could also throw the Oil light when wet? I've got an '07 WRX (wagon, how'd you guess), Stg.2 and almost had an aneurism when I saw that light. It was a very humid/wet day yesterday, light was on at night when I moved the car, and off this morning. Oil level is normal and clean. Thanks for the explanation.
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Old 12-04-2012, 12:24 PM   #15
Frank-i-e
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Well my light went off because it was touching a metal hard line. Is yours off of the motor or still in the block?
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Old 12-04-2012, 01:39 PM   #16
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Anything causing a short will cause the light to go off.
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Old 12-04-2012, 05:45 PM   #17
the suicidal eggroll
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Quote:
Originally Posted by wagonsarewinners View Post
So are you saying that a factory switch installed as such could also throw the Oil light when wet?
Yes, but usually water will only create a partial ground so the light will be dimmer than if the pressure was low and the switch activated.
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