2000 Bonneville, gauges cycle when you turn on the switch but the fuel gauge doesn't read correctly and the oil pressure pegs out at 120 psi. Other gauges seem to be correct. Is this a harness problem or could the sending units both be bad at the same time? Thanks.

Seperately it would sound like the sending units. Many have replaced the oil pressure sender, and many 00 models for GM needed to have a fuel tank sender replaced as well.

From what you say, it sounds like they both failed at exactly the same time. Is that correct.

So...you are saying that all the gauges cycle (or peg out) at start up (which is normal), but that the oil and fuel gauges do not go back to where they should? If so, then yes, I'd have to agree with Bill.... it seems odd, however, that both sending units would go kaput at the same time.

....<thinking out loud> .... what else would cause failure besides the sending units? Bad wire connection in the harness or in the dash? Is there a fuse that controls these?

Thinking about this further. Uhless someone else chimes in before hand..

I don't think I've heard of any wiring problems with 00+....although the possible vapor barriers on the doors leaking could be a problem if you carpets feel soaked.

I would probably pick up the oil sender and replace, they are reasonably inexpensive. if that fixes up the oil, then it'* unfortunate because then the fuel sender needs to be done.

The fuel sender is a part of the whole fuel pump assembly that goes in the tank right? I believe that in the 2000+ models you can access that from the trunk and it isn't a PITA like it was for the earlier units.

Sorry..I meant to stress that the fuel sender was not typically inexpensive as a part.

Both going out at same time sounds odd, but I've had to replace both of these sending units on my 2000. Not too bad or overly expensinve to perform.

Thanks guys for the reply. I'll try replacing the oil pressure sending unit to see if that works. If so I guess I'll tackle the gas gauge sending unit. If you could provide some more info on accessing the gas tank through the trunk I'd appreciate it. Thanks, DG

There is an access panel under the carpet in the trunk, closer to the back seat. If you pull the carpet back, you'll see it. Remove that, and the fuel pump, with the sender attached is under it.

Before you do that, how long has the gas gauge been flakey, and where do you buy your gas? I think that it was last year, so it may not still apply, but Shell gas had some high sulfer content that was screwing up the senders on many cars, including GM'*. Changing gas brands and waiting a few weeks, the gauge would start working again.

Alright, there are 4 gages on the instrument cluster that go through a sweep routine, initialization so to speak when the engine is started. The 4 gages are from left to right across your instrument cluster: Oil Pressure, Engine Coolant Temperature, Fuel Level, and Battery Voltmeter. They all deflect to full scale twice, then indicate nominal values at the end of the starting sequence. I must align myself with the replies already posted here in that I believe the corresponding sensors (Oil Pressure, Fuel Level) are potentially at fault. I know when the Oil Pressure Sensor fails, it fails to maximum pressure-120 psi. The Fuel sending units on these H platforms have always been prone to failure and give spurious indications when failing. But the others are correct, you can access thae Fuel Level Sender Assembly from the access in the trunk, where as on the older generation Bonnevilles, you had to drop the fuel tank out the bottom to service.