Question: 1990 C4 Coupe: That pesky Check Gauges warning light trouble shooting

[AV8R]

Every so often, the CHECK GAUGES warning light comes on, sometimes bright and others faint or winkingly. What Im looking for is for expert and experience in trouble shooting the source of this problem and perhaps a schematic diagram. From reading other posts here regarding similar issues, it was said that this light is not driven by an ECM or other controller, rather the oil, water, temp and battery sensors. Somewhere I read that even low fuel can set this off. Which indicates any of these sensors, gauges and their connections may be the culprits.

In my case, as you can see from the picture below, all the gauges are running true and in good status, plus a full tank of precious fuel; yet there we have the Check Gauges warning light. It matters not if in idle or running down the road. I do have one confession to make... I can make this happen almost at will, so its not a mystery of when it happens, rather how it does and where exactly to look to fix it. Im thinking its either a bad ground or intermittant PCB or gauge. The pathology is this: I wash the car with a lot of water via garden hose, and this can cause the light to come on. After waiting about 4-6 hours on a warm sunny day, and the problem goes away, after whatever got wet dries up.

So maybe something under the hood is getting wet, or maybe water is getting into the gauge area (not as likely as its dry inside). WHere would I look for the grounding wire or whatever sensors that are most likely to have been affected? Or what else that Im not aware of?

Note that when I drive this car on a very rainy freeway (and they are rare out here), it doesn't happen. Theres something about using the hose that doesn't happen with overhead rain or underbody splashing. Sure the solution is to not wash the car with the hose, but Id like to figure this one out.

Thanks in advance,

 

[boomdriver]

I'd sure start with the connections and grounds...often signals that are weak or inconsistent will cause some
odd quasi-alert to appear. These digital displays work on variable resistence, so its not as B/W as it is in the analog world of displays..it might be getting enough of a 'trigger' to set one display but not the other since it IS a dual display.
We need more warning indicators to indicate to check the warning indicator...... :eyerole

I wonder why the GM engineer that was in charge of displays didn't build in a warning indicator to indicate that the "check gauges" indicator may be faulty?

 

[K & B Special Products]

Check & clean the ECM connectors-water is the clue.

 

[AV8R]

Is the ECM you're referring to that affects these gauges, the rectangular unit under the hood on the left hand side and next to the windshield and brake master cylinder?

So I need to clean these contacts and look for ways the cable or connector can get wet, is that the correct inspection?

If so, perhaps spraying the hood where it meets the windshield is the probable cause.

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