Low oil light illuminated with full oil

[BlackbirdZ07]

I just finished a bunch of work on my '90 including new injectors, etc. Before I started, the low oil light was on but the oil was full. I replaced the oil pressure sensor AND the oil level switch on the oil filter housing with new GM parts. Also changed the oil.

I've added 9.5 quarts and the dipstick indicates that the oil level is at the full mark. I had to add that much because I also removed the oil pan to replace the gasket, so I got all the oil out of the pan. I used Amsoil 10W30.

After all the work and the oil change, the LOW OIL light still comes on when the car is running, but the oil is full. Any ideas why this light is on?

[VetteMed]

oil level sensor is on LH side of the oil pan, not on the filter housing. Filter housing has oil pressure switch, oil pressure sensor, and oil temp sensor.

My guess is either a bad oil level switch or a short in the wiring. It does run fairly close to the exhaust.

[BlackbirdZ07]

oil level sensor is on LH side of the oil pan, not on the filter housing. Filter housing has oil pressure switch, oil pressure sensor, and oil temp sensor.

My guess is either a bad oil level switch or a short in the wiring. It does run fairly close to the exhaust.

Ah, thanks for the information... I thought the switch was for oil level but what you said makes perfect sense. I don't remember disconnecting a sensor on the oil pan when I removed the pan, and I'm sure I didn't reconnect one when I reinstalled it. I'll get under there and do some investigation. Thanks!

[BlackbirdZ07]

Okay, this is weird. I just got under the car and checked, and my car DOES NOT HAVE an oil level sensor. I can see the boss on the left side of the oil pan where a sensor would go that matches the picture in the FSM (except it shows it on the right side), but there's no hole in the boss for a sensor. No connector or wiring for a sensor either.

So, did some '90s not have oil level sensors?

Either way, I guess I'll solve my problem by removing the light bulb from the DIC. There was no bulb installed when I got the car but I put one in.

[sammy]

my 90 doesnt have the sensor either .but my 92 does

[BlackbirdZ07]

Thanks. I wonder how many '90s (if any) have the sensor. It's described in the FSM and the manual provides the torque specification.

[VetteMed]

That's right... some or all 90s did not have the sensor -- so I don't understand how you can be getting a low oil light without the sensor there. Perhaps 90 has the wiring harness connector and you pinched or shorted it while doing the recent work?

[GOLDCYLON]

That's right... some or all 90s did not have the sensor -- so I don't understand how you can be getting a low oil light without the sensor there. Perhaps 90 has the wiring harness connector and you pinched or shorted it while doing the recent work?


Maybe this 90 light is being fed via the ecm signal generated by one of the sending units on the bottom side of oil filer housing? Its one of the bottom two sending units.

[XfireZ51]

However, you do have oil pressure correct?

[VetteMed]

Maybe this 90 light is being fed via the ecm signal generated by one of the sending units on the bottom side of oil filer housing? Its one of the bottom two sending units.

I suppose it's possible that the low oil pressure switch might trigger the "low oil" light? Come to think of it, there is no low oil pressure warning lamp, so what would that switch trigger otherwise??

[GOLDCYLON]

I suppose it's possible that the low oil pressure switch might trigger the "low oil" light? Come to think of it, there is no low oil pressure warning lamp, so what would that switch trigger otherwise??

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

[VetteMed]

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.

[GOLDCYLON]

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.

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

[BlackbirdZ07]

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.

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.

[BlackbirdZ07]

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

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.

[BlackbirdZ07]

I suppose it's possible that the low oil pressure switch might trigger the "low oil" light? Come to think of it, there is no low oil pressure warning lamp, so what would that switch trigger otherwise??

Maybe the Check Gauges light??

[VetteMed]

Maybe the Check Gauges light??

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.

[VetteMed]

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.

[VetteMed]

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.

[BlackbirdZ07]

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.

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

[VetteMed]

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

Keep in mind, that info is for 1991, I don't have the diagrams for 1990, so it may be worth confirming that the same information is accurate.

-Andrew