Hi Joe; Randy here. I saw your post earlier but felt someone more knowledgeable would answer. Unfortunately I have the site owners fooled into thinking I'm smart so they asked to me to give it a shot. I'm not familiar with this system, but I can share some information on that type of fault code. You'll probably need the manufacturer's service manual to follow through.
Some fault codes reference a sensor. Those are electrical problems related to it half of the time and the wiring associated with it the other half of the time. Diagnosing those are pretty similar for most sensors on most brands of vehicles. The code you have refers to an unacceptable operating condition that may not be electrical in nature. What I don't know is if it means that condition is the result of a defect or if it's the defect causing the unacceptable condition. Are there any symptoms besides the fuel gauge?
To test the gauge circuit involves unplugging the wire to the sending unit at the fuel tank. If you have dual tanks and the gauge drops to "empty" on both of them, it's a wiring problem. If only one tank acts up, it's the sending unit or a connection related to it.
To test the sending unit, you would need to find it on the wiring diagram in the service manual to see which wire, by color, is the one in the connector. Simply unplugging the entire connector should make the gauge read maximum one way. Grounding the wire should make the gauge read maximum the other way. GM fuel gauges used to go to maximum "full" when the sending unit was unplugged, and I think they still did that in '99, but newer vehicles need to add a miserable computer to complicate the issue, and those gauges may not work the same way. Regardless, you should see a definite change between when the wire is unplugged and when it's grounded.
Another thing you might consider is if there's an electric lift pump in the tank and the tank is rusty. '90s Blazers with steel gas tanks had a common problem of losing the ground for the in-tank fuel pump when the tank got rusty. The often-overlooked clue was that the fuel gauge went to "full" because it also lost its ground. If you have a no-start or stalling condition, take a look at that. The fix is to drill a hole in the tank outside of the pinch weld, run in a self-tapping screw, and attach a new ground wire to it and to the body or frame.
If you need a service manual, there's nothing better than the manufacturer's stuff on paper, but the next best thing has a link at the top of this page under "Repair and Service", then "Manuals". It's a subscription to "Mitchell" manuals. They do a real good job with their electrical diagrams. Everything today is relatively hard to follow, but theirs are easier to use than what's in the GM manuals. There are dozens of diagnostic manuals from the manufacturer that are vastly different than the service manuals. You have to buy those separately, but I think they are included in Mitchell as part of their service. Diagnostic manuals lead you through each step of the troubleshooting procedure. There's a separate procedure for each fault code.
If none of these things help, let Mike know and he will make things right with you. There's another fellow here who is pretty knowledgeable on GMs. His name is Wrenchtech. He may have not seen your post yet.
Tuesday, July 1st, 2014 AT 3:46 PM