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Discussion Starter #1 (Edited)
Real 1995 Impala SS with 135,000 miles. A couple days after I had the rear main seal and oil pan gasket changed by a reputable shop I noticed my oil pressure needle flicker a bit. I can’t recall if it was flickering from normal operating range to the high side or from normal operating range to low. Anyway, I remember it getting my attention from the noise it made when it did that. This was a few years ago. I changed the oil pressure switch out with an auto zone oil pressure switch (switch ps188– noted “with light”). The new autozone duralast oil pressure switch did not solve anything. I’m wondering a few things.

1. Is the ps188 “with light” switch the correct switch for the 1995 Impala SS? I’m asking because I remember the auto zone guy asking if my car was the “with light” or “with guage” type. I chose the “with light” switch because I was already aware that these cars are an idiot light type guage.

2. Is my switch, that I had taken out, the original oil pressure switch from the factory? It says Hi-Stat 25036832. And what brand is my original switch? I can’t seem to find a Hi-Stat brand anywhere. What brand is my switch? Can I test my switch and how?

3. I unplugged my oil pressure switch, under the hood, when the vehicle is running and the guage does not move at all from this high position. It stays in the high position. Does this mean that the switch is not the problem? Could autozone have gave me a used switch? As I said, this all started by flickering and then going to high all the time.

Note/s: when I have the key in the “off” position, the guage is all the way left on the low reading. When I turn the key to the “on” position, the guage jumps to between low and mid, (which I personally believe is normal). *Finally, when I start the car, the needle forwards all the way to the maximum high reading to the far right. I have my cluster glass off because I removed the fuel guage and oil pressure side of the cluster to check for contact failure or shorts. It looks good. I can turn the oil pressure needle 360 degrees. There is no pegging like others describe. It just electrically returns to this high reading spot. It’s all resistance to position on the reader panel if you will. I have already fixed soldering points to revive my digital speedometer in the past. Still works. Pictures are of the old switch that came with the car. Thanks.
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From the FSM: A two position switch opens with oil pressure greater than 3 psi.

So when the switch is unplugged and the ignition is on the gauge should show 3/4. If you jump the switch connector to ground the gauge should move to the left and be in the low end. (0)

If these two tests do not give you normal results you have a wiring problem or a bad ground. G202 is in the passenger's side kick panel. The resistor is taped in the wiring behind the glove box.

The gauge requires power to move so it is normal for it to remain in the normal 3/4 position until you turn the key to run, it should then go low until you start the car and have oil pressure then it should go to 3/4.

The oil sensor switch should be a good ground until there is oil pressure when it "opens" and should be off.

Click on the link below for Goldswagon's diagram:

 

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Discussion Starter #4
From the FSM: A two position switch opens with oil pressure greater than 3 psi.

So when the switch is unplugged and the ignition is on the gauge should show 3/4. If you jump the switch connector to ground the gauge should move to the left and be in the low end. (0)

If these two tests do not give you normal results you have a wiring problem or a bad ground. G202 is in the passenger's side kick panel. The resistor is taped in the wiring behind the glove box.

The gauge requires power to move so it is normal for it to remain in the normal 3/4 position until you turn the key to run, it should then go low until you start the car and have oil pressure then it should go to 3/4.

The oil sensor switch should be a good ground until there is oil pressure when it "opens" and should be off.

Goldswagon's diagrams are here: Click the "A"


The diagram you want is:

Actually I had it wrong a bit. When, I put the key in the ignition, the needle is already on maximum high. When I turn the key to on position, it goes to about just below half. When I start the car, the needle flips all the way to high again. When I turn the car off, the needle stays in the maximum high position until I turn the key to the on position again repeating the just below half reading.

Note: When I unplug the switch behind the intake, turn the key to the on position, it flips all the way to high which is different from when it’s plugged in (goes to below half when plugged in) so that means it makes a difference plugged in or unplugged.
 

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Discussion Starter #5
Both photos are with car off. Both photos are with Key in on position. The below half reading photo is with the key in on position with the switch “Plugged in” and the high pressure photo reading is with the switch unplugged with the key in the on position. One exception is with the car running, the pressure reading (needle) flips to the maximum with the sensor plugged in or not.


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Discussion Starter #6
Actually I had it wrong a bit. When, I put the key in the ignition, the needle is already on maximum high. When I turn the key to on position, it goes to about just below half. When I start the car, the needle flips all the way to high again. When I turn the car off, the needle stays in the maximum high position until I turn the key to the on position again repeating the just below half reading.

Note: When I unplug the switch behind the intake, turn the key to the on position, it flips all the way to high which is different from when it’s plugged in (goes to below half when plugged in) so that means it makes a difference plugged in or unplugged.
From the FSM: A two position switch opens with oil pressure greater than 3 psi.

So when the switch is unplugged and the ignition is on the gauge should show 3/4. If you jump the switch connector to ground the gauge should move to the left and be in the low end. (0)

If these two tests do not give you normal results you have a wiring problem or a bad ground. G202 is in the passenger's side kick panel. The resistor is taped in the wiring behind the glove box.

The gauge requires power to move so it is normal for it to remain in the normal 3/4 position until you turn the key to run, it should then go low until you start the car and have oil pressure then it should go to 3/4.

The oil sensor switch should be a good ground until there is oil pressure when it "opens" and should be off.

Goldswagon's diagrams are here: Click the "A"


The diagram you want is:

Do you know how to do the ground test from the plug? There are three pins in the connector. Like, which of the 3 pins do I jump and to where? Thanks for the reply and information you provided.
 

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The tan one.
Ign on ,tan disconnected, should read 3/4.
Ign on ,tan grounded, should read low.


If
Ign on, tan disconnected, reads high or over high.
Ign on tan grounded reads low, possibly the ground at the right kick panel is disconnected. Or if you are not the original owner, possibly the resistor has been disconnected.
This so a transducer ,like from a 9C1 , could be used and the gauge would act like a real gauge .
All this assuming the guage and or needle has not been screwed with.
 

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Discussion Starter #8
The tan one.
Ign on ,tan disconnected, should read 3/4.
Ign on ,tan grounded, should read low.


If
Ign on, tan disconnected, reads high or over high.
Ign on tan grounded reads low, possibly the ground at the right kick panel is disconnected. Or if you are not the original owner, possibly the resistor has been disconnected.
This so a transducer ,like from a 9C1 , could be used and the gauge would act like a real gauge .
All this assuming the guage and or needle has not been screwed with.
I jumped the tan wire (center pin on plug connector) with the key on and the needle goes to below half reading. When I start the car, the needle remains in the same half reading. When I turn the key to off position, the needle still remains in the below half position.

When I disconnect the jumper wire, (center pin tan wire on plug), with the plug connector still disconnected, turn the key to on position, the needle shoots up to just past high. When I toggle the key back to off position, the needle jumps back slightly to exact high. Turn to on and the needle, jumps up a tad to the past high position. When I start the car, the needle stays on high-plug still unplugged.

When I plugged the connector back on the oil pressure switch, the needle is below half. When I turn the key to the on position, the needle stays the same ( with oil pressure switch plugged in). When I start the car, the needle shoots up past high ( with oil pressure switch plugged in).
I’m guessing it has to be getting a good ground at the right kick panel. I checked the right kick panel ground. I loosened and re tightened it. It seems good. I’m guessing my center pin test shows it’s getting a good ground? I wonder if the resistor behind the glove box can go bad? IDK.

One funny note: the first attempt to ground the center pin made the needle shoot all the way left until it pegged against the fuel measurement. When I tried to reproduce the far left test result, it wouldn’t do it again for my brother who I tried to show what I was doing. I blew the fuel pump fuse under the hood at the firewall box. I replaced the fuse and repeatedly got the results I explained above. Thanks again to you both. More direction/opinions welcome. Thanks
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Discussion Starter #10
Just for kicks, while we are here, when I purchased this car, the speedometer and odometer was intermittently going off and on until it stopped working. I re soldered some of the posts that were cracked around the posts/pins that go through the board. Loud sound systems and low profile wheels don’t help I imagine and may contribute to this. After re soldering, my speedometer and odometer never failed since. It’s been years of continuous good working function. I wonder if a resistor in this cluster or another soldering area is cracking?
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Key on, center plug wire (tan) jumped to ground photo.
Grounding tan with ign on, the needle should go to low, in the red.
You either have an issue between the cluster and the sender or something wrong at the cluster, i think.
I might have a 95 cluster here to check pin outs.
Think you might want to pull the cluster and bench test.
Resistor or not , resistor grounded or not, the needle should go low ,red zone, grounded tan wire.

Ignore what the needle does ign off, it means nothing.
 

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I like a good bench test as much as the next person, maybe more. But would it not be worth a little time to pop the glove box door and wiggle the harness.

For me the next step would be to check for ground and voltage at pin A5
of C1. Why play with the cluster if the wiring never grounds the input pin?
 

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My reasoning for bench testing is that is all i have here , an old cluster.
The plug and pin orientation is quite confusing as one is upside down compared to the other.
The correct ground for the actual guage is on the other plug.
The ground pin on the left plug will run the check gauges module and the guage will go to low when you ground the brown wire but without the ground shown in these pictures the guage will not work correctly.
The three wires in the pictures below will test the cluster and gauge.
I used pcm pins.

Ground tan, needle goes to low red
Open tan , needle goes right off the end of high.
In operation with resistor in harness, it would go to 3/4 scale.
When bench testing, if left side B3 ground is in place also, the check gauges light will also come on after a few secounds of grounding the tan wire
 

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To add,
The important gauge ground , right plug A6 black /white circuit 351
Goes through splice S200 the goes to ground G202 right A piller.

The left plug ground B3 ,while important, is not responsible for the oil gauge.
It is circuit #450
It goes through c202 then c201 then to G200 Left A pillar .

Thats all I got.
 

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Discussion Starter #18
Update**I found a cracked soldier post joint and possibly more than one above and below speedometer. I went ahead and re soldiered them all. I’m surprised it still worked. I guess it was still getting a contact or did not need one. It did not fix my oil pressure problem though.
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