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Discussion Starter #1
Quick question. Should the check oil light come on before starting with key on engine off? If so what tells the light to come on only at that instance if the oil level is full. I'm trying to determine if the sensor is bad. This is specifically for a 1990 gt.
Thanks in advance.
 

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Remove the wire from the sender and ground it. See if the light comes on when the ign is switched on.
 

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Discussion Starter #4
Remove the wire from the sender and ground it. See if the light comes on when the ign is switched on.
Sorry I didn't mention. I already did this and the light comes on when I ground it. But with out knowing if the sensor is supposed to come on with key on engine off I didn't have a way of telling if the sensor is good since the oil is full. Short of draining some of the oil out.
 

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Discussion Starter #5
+ 1

Normally all of the cluster lights should come on at initial key on because of the "lamp test".
Thanks for the input. I didn't know about the lamp test. Is this a separate circuit? Looking at the back of the instrument cluster it looks like the only thing grounding the low oil indicator light is the grey wire from the low oil relay, does the lamp test run through this relay?
 

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Thanks for the input. I didn't know about the lamp test. Is this a separate circuit? Looking at the back of the instrument cluster it looks like the only thing grounding the low oil indicator light is the grey wire from the low oil relay, does the lamp test run through this relay?
I always thought the "lamp test" was a separate function. That way the only thing that the lamp test depends upon is the lamp itself. But try it for yourself. Disconnect the sensor. Turn the key on but do not crank. Does the light come on during the lamp test?
 

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Discussion Starter #7
Thanks for the input. I didn't know about the lamp test. Is this a separate circuit? Looking at the back of the instrument cluster it looks like the only thing grounding the low oil indicator light is the grey wire from the low oil relay, does the lamp test run through this relay?
I always thought the "lamp test" was a separate function. That way the only thing that the lamp test depends upon is the lamp itself. But try it for yourself. Disconnect the sensor. Turn the key on but do not crank. Does the light come on during the lamp test?
The lamp doesn't come on unless I ground the wire at the low oil sensor, that's my whole issue. If the lamp is supposed to come on with key on engine off (before cranking) I want to know what controls that, whether it's a "lamp test" circuit or what. Since my oil is full the light doesn't go on with the engine running regardless of if the low oil sensor is bad or not.

So really I need to know what makes the light go on at key on engine off.
 

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if you look at a wiring diagram, it will be self explanatory
 

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Discussion Starter #9
if you look at a wiring diagram, it will be self explanatory
I did and that's why I'm asking now if it is supposed to come on at key on engine off.

It looks like the only thing that would be controlling it at key on engine off is the splice bk/lb wire from the ignition switch. But I don't know the inner workings of the relay to say for sure.
 

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Discussion Starter #10
If I knew for sure that the low oil light is supposed to come on at key on engine off that would help me diagnose it.
 

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so do you see how it works?
 

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Discussion Starter #13
So rd/y from the fuse and blk ground energize the relay. Gy is the ground path to the indicator light, which is closed by the bk/lb when the key is forward and also the w/pk when the oil is low determined by the sensor. Sound correct?
 

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good

but how is the bulb test done?
 

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Discussion Starter #15
good

but how is the bulb test done?
I thought the bulb test for the check oil light was done through the bk/bl wire from the ignition switch when the key is on before crank and engine running? That's what I was implying in my last post at least.
 

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look a little closer

the ignition switch provides a ground in ‘start’ and the load is the ‘cel’

The blk/lb going to the timing relay is just a monitor

It senses voltage hi or low

The ‘oil light’ goes to the timing relay

The timing relay is therefore the source of the bulb check, its the ground switch for the oil light

The timing relay is the key here, its not just a relay it has a timing circuit
 

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Discussion Starter #17
Thanks for the description. So the timing relay works by allowing the ground path to the gy wire to be closed for only a certain amount of time. After that time the w/pk wire to the low oil sensor is the only thing to close the ground path?

You said the bk/lb is a monitor that check voltage. Can you explain what the purpose of that is? I'm trying to determine if the relay is bad.
 

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the timing module has a power and ground

its always energized

the purpose of the timing module is to supply

a bulb test and to allow the low oil condition to light the bulb

the oil can be sloshing in the pan

that oil level switch can be opening and closing as the sloshing is happening

your low oil bulb can start flickering on the IC

to prevent the flickering the timing circuit is employed

a certain time must elapse with the switch closed before the light is illuminated
 

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if you want to test the switch

you will need to simulate a low oil condition
 

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Discussion Starter #20
if you want to test the switch

you will need to simulate a low oil condition
Ok. I understand that. But I thought the bulb test was supposed to happen with the key forward at run before crank. When I turn the ignition to start the light comes on and turns back off once I let off the key and it goes back to run.

What would really help is if someone could tell me when the light is supposed to come on when the oil is NOT low. At run before start? Only during start? It looks like from the schematic only at start when you hold the key forward.
 
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