Check oil light issues

[cchase]

This is on a 2002 Chevy Malibu. It is equipped with an oil level sensor to warn you if the oil level drops to an unsafe level. It is basically a little float switch, though I am not specifically sure whether it is an actual switch or just a resistor.

For the past year or two, the Check Oil light (not to be confused with an oil pressure light - this one is only for the level in the pan) stays on intermittently. According to the literature I have, the computer only "checks" the level in the brief period between Key On and Engine On.

I initially figured it had to be a flaky sensor, since it's 11 years old, so I replaced the sensor with a new one (of course forgetting to manually manipulate the switch with a multimeter to see what it actually does).

Replacing the sensor has had no impact on the operation of the light though, it's just as intermittent as ever.

Since warm weather has now come, yesterday I spent some time probing with a multimeter to work through this issue, but I'm not coming up with anything that makes sense.

The plug to the sensor registers 0V when the engine is off, as expected, and 12V when the Key is On, as expected. The sensor is reading infinite resistance, which I don't know the significance of particularly (whether it should be infinite or zero).

I decided to fool the computer so I unplugged the sensor and started the car. The Check Oil light did not come on. So I figured ok - infinite resistance is considered acceptable level (which seems backwards to me but is kind of irrelevant). Next, I shut the car down, then stuck a paperclip between the harness-side plug to short out the connector - a zero ohm reading. I figured that this would trigger the Check Oil light, but it did not. It still went out.

So I'm left at the point where the plug has reliable voltage but it doesn't matter what the sensor reads, since the Check Oil light wouldn't come on yesterday no matter what I did.

What am I overlooking here? At this point it's irrelevant whether the sensor is working at all since I can't manually trigger the Check Oil light.

And as a "are you sure it has gas in it?" disclaimer - the oil level is correct in the car.

 

[KrisZ]

As with any switch infinite resistance means the switch is closed and close to 0 Ohms means the switch is open.

Your lack of results could be computer programming. I highly doubt the switch is directly wired to the lamp, but instead, the computer probably has a logic that will trigger the light, so without factory manual this could be tricky to diagnose if you don't know the exact conditions that turn the light on.

If I were you, I would simply unplug the sensor, unless the cars burns lots of oil and you really want that warning light.

 

[dishdude]

Sometimes these GM level sensors would through an erroneous light if the car was parked on a hill, or the engine was shutoff and restarted before the oil drained into the pan. The sensor may have to go to ground and not be a paperclip also...

 

[TFB1]

Originally Posted By: KrisZ
As with any switch infinite resistance means the switch is closed and close to 0 Ohms means the switch is open.


Huh??? I learned infinite was infinity meaning unmeasurable ohms or open circuit...Zero ohms would indicate a closed circuit...

Ford's version is closed at low level(low to zero ohms) and incomplete(open) circuit if the float opens the connection... Those also would sometimes give a false warning if the vehicle was parked with the left side somewhat higher than right...

 

[440Magnum]

Originally Posted By: KrisZ
As with any switch infinite resistance means the switch is closed and close to 0 Ohms means the switch is open.



Other way around.

 

[cchase]

Originally Posted By: KrisZ
If I were you, I would simply unplug the sensor, unless the cars burns lots of oil and you really want that warning light.


I'm not sure whether unplugging the sensor is going to fix the problem. I don't know how GM does it, but if I were designing the system, I'd make an open switch trigger the Check Oil light, since a broken switch would likely fault open, not closed.

Either way, since I'm not noticing a difference with the sensor unplugged, I really have no guarantee that it won't still display the Check Oil light anyway so I'm not sure it would work as a solution, even if I could live with knowing it wasn't working (which I can't).

Originally Posted By: dishdude
Sometimes these GM level sensors would through an erroneous light if the car was parked on a hill, or the engine was shutoff and restarted before the oil drained into the pan. The sensor may have to go to ground and not be a paperclip also...


Yes, the manual itself does mention that parking on a hill can trick the sensor, etc. Although to be fair, I think the oil level would have to be very low to trigger the light, even on a hill, because it's only in the bottom inch of the pan.

However, this happens on flat ground, inclines, etc. with no pattern. And it triggers most frequently on the first start, not subsequent. But, it will sometimes not turn on ever, and sometimes it will not trigger on the first start but will on subsequent starts...



I do agree that it is probably not a direct route from the sensor to the idiot light on the dashboard, but I can't envision the logic failing in what is basically a solid state processor - at least not so that it wouldn't be coming on randomly while driving, for example.

 

[KrisZ]

Originally Posted By: 440Magnum
Originally Posted By: KrisZ
As with any switch infinite resistance means the switch is closed and close to 0 Ohms means the switch is open.



Other way around.



Yup, thanks for correcting me, had it correct in my mind, but didn't type it out correctly.