Fuel and Oil Pressure Gauges

[Hungrycat7]

Hello All. 2000 SLE with just shy of 100K on the ticker. About 3 months ago I noticed the fuel gauge was not working correctly. 300 miles on the tank and it read 3/4 full. Filled the tank and the guage has been pegged on Full ever since. When I start it up in the morning and let it run the gauge will slowly creep down to the correct level until I put it in gear. The second I put the car in gear the fuel gauge quickly rises back to the full level and remains there for the remainder of the day. The on board computer always says 400 + miles until empty and the "gallons used" is always one gallon short. (It will say I have used 10.5 since the last fill up and can usually put 12 in it.) The last time it was in the shop I asked about it and they said it was most likely a wiring issue. I have been living with it, just using the trip odemeter ever since. This morning when I started it up I noticed the oil pressure gauge is now pegged at the highest possible level. I shut it off and started it back up and it is still there. Drove it over 100 miles today, starting it multiple times and the guage is still not functioning. Checked the oil, it is clean and the level is full (but not over full). My question is: Does this sound like the cluster is going bad or do I have a more serious issue? Any help would be greatly appreciated!

On what may be a completely unrelated note: The ABS, Trac OFF, and Brake lights are all illuminated. Car has been to shop several times for this issue. Front hubs, wheel speed sensors have been replaced. All three times the car was in the shop the lights would be off for a few months but always come back. They have no idea why they are on this time and I do not want to pay dealer fees to find out what it is. I really am not concerned with this and do not think it is related to my gauge issue but I thought I would give you experts all the info I could. Thanks

[Tech II]

When you say shop, I know it's not a GM dealership......because if it was, they would have told you, right away, you need a fuel sending unit, that is accessed through the trunk(tank doesn't have to be dropped).......can be verified with a variable resistor...

Sounds like the oil pressure issue is the oil sending unit.....start the car, if it pegs, shut if off....disconnect harness from oil sending unit....start car.....if it stays on zero, you need a new sending unit( good tech would verify this by quickly attaching a mechanical oil pressure gage)....

Your ABS problems are probably another different concern.....I don't know what your "shop" did, what the codes were, and what codes are now....hubs/speed sensor is one unit...car was in 3X's....time to go elsewhere.....especially when a "shop" has no idea why a light is on....and yes, I am a GM tech......I take pride in fixing things right the first time, with no comebacks......When you go to a GM shop, ask for their best diagnostic guy.....or go to "shops" and keep paying to have you vehicle fixed, the second, third and fourth time.....

[Hungrycat7]

Thank you for your response and, in advance, I apologize for my ignorance but what are the consequences of not fixing these sending units?

[Tech II]

As for the fuel gage, wouldn't rush on that because you can check mileage between fillups with your odometer....

Oil pressure gage is a different story.....the gage is probably bad, and if your oil pressure goes low, you would never know until it's too late and the engine starts knocking...

Also, ABS should be checked out too......when it comes to brakes, you don't want to be driving around with that system in question.....