Unplugged Oil Pressure Switch

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Can someone verify that if you unplug the oil pressure switch that your dash gauge still reads about 40 psi?
 

freddyboy61

Member
Dec 4, 2011
276
Since the oil pressure sensor on the I6 is just a switch closure and the gauge reports a fixed reading established by the PCM, I would have to assume that with an open circuit (unplugged), that would equal zero oil pressure. The sensor closes a switch circuit when a predetermined oil pressure is attained and the PCM drives the gauge to read about 40 - 50 PSI based on the switch closure and RPM.
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
What a complete pile of UNengineered shit ! I have been driving with the sender unplugged for days and i have no warning lights or low pressure gauge. It shows everything fine at 40 psi. I would never know if my oil pressure got low.
 

silverunicorn

Member
Dec 4, 2011
327
CaptainXL said:
What a complete pile of UNengineered shit ! I have been driving with the sender unplugged for days and i have no warning lights or low pressure gauge. It shows everything fine at 40 psi. I would never know if my oil pressure got low.

Which is EXACTLY why I had to replace my motor in my 2006.

Just sayin'

Chris
 

Sparky

Member
Dec 4, 2011
12,927
I thought the switch was closed when there was enough oil pressure, and open when the pressure dropped below a set level? Is it really the other way around? That's so dumb... dumb x2 because it should be a sensor and not a switch in the first place.
 

AtlWrk

Member
Dec 6, 2011
674
Sparky said:
I thought the switch was closed when there was enough oil pressure, and open when the pressure dropped below a set level? Is it really the other way around? That's so dumb... dumb x2 because it should be a sensor and not a switch in the first place.

Found this hard to believe so I just went out and unplugged the oil switch and started up. No indication that anything was wrong. Oil pressure at 40+.
:confused:

Checked the continuity at the PCM connector and sure enough, engine off = pressure switch is closed, not open.:eek:
 

Dshow

Member
Dec 7, 2011
68
They do this so they can detect an open circuit/broken wire when the TB is first key'd on.
 

Mark20

Member
Dec 6, 2011
1,630
Dshow said:
They do this so they can detect an open circuit/broken wire when the TB is first key'd on.

Strange the PCM is not throwing a code and idiot light since a disconnected sensor would be an open circuit/broken wire.
 

Dshow

Member
Dec 7, 2011
68
Theoretically, that's why, but who knows what they actually do in their software...
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Looks like the switch grounds to the block when pressure is low. There shouldn't be a light when unplugged.
 

khill

Member
Jan 7, 2012
86
Yep, oil pressure switch is idiot light only, just like the oil pressure gauge. The truck doesn't ever measure the actual oil pressure, it only displays a computed estimation of where some performance table guesses the oil pressure might be. If you have a bad or disconnected switch, you could drive with no oil and your truck wouldn't know a thing (until you seize/blow up) .
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Ok, after reading up a little more it looks like it doesn't ground to the block.

It looks like the switch itself is a simple 12 volt single pole diaphragm actuated relay. I connected the purple and tan/black wires together and this is what the dash looks like. The "check gauges" light is on and the oil pressure is near 0. Hmm wonder why its not exactly 0?

Going to continue to test this and see next if the switch itself has any resistance between the two terminals to see if it's a switch or sensor.
 

Attachments

  • 2012-07-28_03-48-52_552.jpg
    2012-07-28_03-48-52_552.jpg
    39.1 KB · Views: 8

Sparky

Member
Dec 4, 2011
12,927
It not being right on 0 might just be a needle placement variance. For example my needle on my temp gauge is slightly left of normal placement.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I guarantee the switch in the I6 is a switch and the sensor in the V8 is a sensor. And the gauge not being at zero is a stepper motor needle issue only.
 

McGMT

Member
Jun 17, 2012
621
Im sorta surprised that when the gauge bottomed out and the check gauge light came on that you didn't get the red oil spout of death light... Or do we not have one? Ill have to check when I hit the key later. Almost as if something else on/in the engine is telling the PCM that there indeed is oil pressure somewhere...
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
the roadie said:
I guarantee the switch in the I6 is a switch and the sensor in the V8 is a sensor. And the gauge not being at zero is a stepper motor needle issue only.

I'm sure your right. Just like to test stuff to satisfy the scientific curiosity in me. I'm kind of "I wouldn't believe it if I didn't see it myself".

I also like to program on the side and am curious if the a/d converter in the pcm is capable of using input from a variable pressure sensor.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
CaptainXL said:
I also like to program on the side and am curious if the a/d converter in the pcm is capable of using input from a variable pressure sensor.
Very cool. 15 years ago, I programmed a PCM test system for testing Motorola units used in Fords. Had to sign a non-disclosure agreement on the Ford specific features, but a switch closure is handled very differently in the firmware than an analog sensor reading. Unless you can hack at a much deeper level than pdmforlessdoes, we're not going to end up with an I6 PCM with the ability to read a V8 sensor. But you knew that. :wink:
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
the roadie said:
Very cool. 15 years ago, I programmed a PCM test system for testing Motorola units used in Fords. Had to sign a non-disclosure agreement on the Ford specific features, but a switch closure is handled very differently in the firmware than an analog sensor reading. Unless you can hack at a much deeper level than pdmforlessdoes, we're not going to end up with an I6 PCM with the ability to read a V8 sensor. But you knew that. :wink:

Ok. I am kind of starting from ground zero when it comes to our PCM's. I was hoping that both the PCB and IC's for the V8 PCM are the same for the I6? Do we have any diagrams of the PCM circuitry?
 

LBB

Member
Apr 5, 2012
53
I have a kind of low oil situation right now and nothing showed me that I have it, besides the oil under my vehicle.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
LBB said:
I have a kind of low oil situation right now and nothing showed me that I have it, besides the oil under my vehicle.

Low oil level is not the same as low oil pressure.

IIRC, 2002 was the only year with a low oil level sensor.
 

LBB

Member
Apr 5, 2012
53
Wooluf1952 said:
Low oil level is not the same as low oil pressure.

IIRC, 2002 was the only year with a low oil level sensor.

If I have no oil I should have no oil pressure I believe.
Does the systems warns me against losing all my oil?
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
LBB said:
I have a kind of low oil situation right now and nothing showed me that I have it, besides the oil under my vehicle.

LBB said:
If I have no oil I should have no oil pressure I believe.
Does the systems warns me against losing all my oil?

IIRC, 2002 was the last year with the Low Oil Sensor, that warned about a low oil level.
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Wooluf1952 said:
IIRC, 2002 was the last year with the Low Oil Sensor, that warned about a low oil level.

And didn't there used to be an oil temp sensor as well? Gotta luv decontenting.
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
LBB said:
If I have no oil I should have no oil pressure I believe.
Does the systems warns me against losing all my oil?

Not all of it obviously. There will still be oil left in the pan well after the pump has lost its prime. But the pickup tube is probably within a couple inches of the bottom of the pan anyway...so..
 

AtlWrk

Member
Dec 6, 2011
674
CaptainXL said:
Ok, after reading up a little more it looks like it doesn't ground to the block.

Have we confirmed this?

McGMT said:
Almost as if something else on/in the engine is telling the PCM that there indeed is oil pressure somewhere...

I suspect the PCM can discern from being able to command the camshaft actuator that there is still, in fact, oil pressure.
 

Forum Statistics

Threads
23,388
Posts
638,719
Members
18,596
Latest member
david herman

Members Online