Re: Low oil light illuminated with full oil
 

With no passenger side block sensor like ALL the MY 91s and some of the MY90s it has to have received its signal from one of the three sendors on the oil filter housing. Its not the oil pressure switch on the top next to the oil filter as that feeds the pressure gauge in the IP (the op indicated that is not a problem). The lower two sending units are the likely culprit. GC

Re: Low oil light illuminated with full oil
 

Well, it would have to be the switch on the side, not the one in the front near the belt tensioner, since that's a temperature sender.

Re: Low oil light illuminated with full oil
 

Concur. There is no other way the ECM would be able to see the data.

Re: Low oil light illuminated with full oil
 

That's what I originally thought that switch was for, but I think VetteMed was right at first because I don't see how it could detect the oil level since it's located on the oil filter housing. Anyway, I replaced it as a preventative measure with a new GM part because I read about the failure of this switch that can cause a sudden and large oil leak, and because it was completely accessible with the other work that I was doing when normally it's very hard to get to.

The bulb was missing along with the Service Ride Control light and the airbag light, so I just assumed someone removed the Low Oil light too. However, since there's no sensor or wiring for a sensor, I suspect the bulb never was installed at the factory, and that the car didn't have a Low Oil idiot light.

And yes, it definitely has oil pressure.

Re: Low oil light illuminated with full oil
 

I'm not sure the light is on because the ECM is seeing data. It may be on because it's not seeing data. In other words, it's not getting feedback from the sensor that the oil level is okay (because there is no sensor), so it turns on the light.

Re: Low oil light illuminated with full oil
 

Maybe the Check Gauges light??

Re: Low oil light illuminated with full oil
 

Yeah, that's a possibility. I need to pore over the wiring diagrams to see if the switch provides a feed to the ECM or it's just grounding a light circuit, and which light it is.

Re: Low oil light illuminated with full oil
 

SO, in a 1991, the CCM controls the low oil light, based on input from the low oil level switch. It's normally grounded (with normal oil level); a break in this ground will trigger the CCM to illuminate the low oil level indicator lamp.

Re: Low oil light illuminated with full oil
 

Blackbird, it looks like you are correct. The low oil pressure switch, which is closed to ground with low pressure, enables the CCM to illuminate the Check Gauges light. I do not see any other input for the CCM that would illuminate that light. Wonder why they didn't make it a "check oil pressure" light.

Re: Low oil light illuminated with full oil
 

Interesting... Thanks for researching that. I'm going out to the garage right now to pull that bulb!