2003 Buick LeSabre Confusing Problem

I have a 2003 Buick LeSabre Limited, and everything was going fine with it till recently. The Fuel gauge started to go haywire as in the needle would go to full, then go back down to a Quarter, then back to 3/4, then drop all the way down to Empty, this is still occurring. At first I believed it to be the fuel level sensor, but then I started to notice something else. A warning message came on stating that the oil level was too low, but when I checked the oil level it was fine, and last night when I was driving with the air conditioner on, I hit a bump and the air conditioner stopped working. I pushed the off button, and was successfully able to make the air conditioner to come back on with out having to restart the car. The horn has also started to go in and out, and I do not know if they are all linked together by a type of computer or if they are separate, any thoughts or ideas are welcomed, I am losing my mind.

One thing that comes to mind is the ground between the engine and the body of the car. The negative terminal of the battery has to connect to the engine and to the body of the car. Trace the negative cable and clean and tighten each connection.

I traced the negative cable, cleaned and tightened each connection as you advised, unfortunately the problems still persist. Any other thoughts?

The fuel gauge signal goes through the BCM (body control module). In fact everything on the dash board display goes through the BCM. Don’t know about the AC though.

Sometimes the float in the gas tank will spring a leak, and sink instead of float, and cause the gas guage to do that. But since these other problems are occuring in parallel, it could be somekind of general electrical problem. I guess the first thing I’d do is take it to a shop and have them do their battery and charging system test. A lot of big box parts stores will do this for free. Still not working after that? I’d get out my DVM and the wiring schematic and measure for reference voltages in the places that are supposed to have referance voltages. Since it is affecting the fuel guage, backprobe the sender unit connector. One wire should have a constant reference voltage (often 5 volts) on it compared to the other. If you can find a schematic, you can determine which side is which by the wire colors. (To read the reference voltage on your DVM, you might have to temorarily disconnect the connector, depending on how it is designed.)

The trouble could be due to a bad ground somewhere, possibly in the dash area, like @Triedaq mentioned. I suspect the trouble is on power side of things to the dash area and is caused by a faulty wire connection to power. Get a wiring diagram for the car and see if there is a common power source to those things you mentioned. It could be from the panel under the hood. Check the voltage getting to fuses in the dash to see if you can see the trouble at that point while the trouble is happening. If none of the fuses at that point show a low voltage issue then the trouble may be on the ground return side. The ignition switch is another possible source of the trouble.

Okay, I spent all day today and yesterday checking and rechecking and just to make sure rechecking the voltage, I found out that one of the horns has a short in it, I never knew this car had two horns. I replaced the horn and now it sounds like a Buick again and not a Hyundai. I decided to see if the air conditioner wires were still intact, and they seemed to be fine. Since that day, the Air Conditioner hasn’t gone out. But I do notice that when the fuel tank is completely full, it tends to show the correct amount of gasoline, and it doesn’t start going haywire till after it goes below half.

All cars have two horns as far as I know. That’s what makes them sound the way they do. It is two different tones.

The gas gauge trouble is most likely due to a dirty spot on the sensor. Try running some Techron in the fuel tank at the next fillup to see if that will clean things up…

You may have to find the ground wire that goes from engine to body. This wire doesn’t always seem to matter but the end on the body should be checked. All cars used to have them in an obvious place. You may have to look for it. On old Toyotas turning on the AC would sometimes stall the engine. I scraped the paint off where it connected and AC would work, car would start and battery would charge properly. On GM cars, the battery would charge, electric windows would work and red light would shut off and wipers would work.