Fuel Gage Way Past Full, Pointing Downward?

Just replaced bad knock sensor on my 02 HD2500 4x4/6.0 (had to remove intake manifold). Disconnected Battery Neg Cable prior to starting the job. When done, reconnected Batt, turned key to On, and Gas Gauge jumped way past Full, to where it is now pointing down, toward the "5:00 O-Clock" direction! Turned key off, then on several times, started it up, drove a few miles, the needle isn't moving at all. Truck had 1/4 tank when I began the work yesterday. Fuel pump/sender is only 3-4 months old, GM replacement. I don't think this could be the sender, since it would max out the gauge at Full mark, right? Can't think of any wires I could have touched under the hood that would do this?
Appreciate any advice, thanks! -Jim.

Just replaced bad knock sensor on my 02 HD2500 4x4/6.0 (had to remove intake manifold). Disconnected Battery Neg Cable prior to starting the job. When done, reconnected Batt, turned key to On, and Gas Gauge jumped way past Full, to where it is now pointing down, toward the "5:00 O-Clock" direction! Turned key off, then on several times, started it up, drove a few miles, the needle isn't moving at all. Truck had 1/4 tank when I began the work yesterday. Fuel pump/sender is only 3-4 months old, GM replacement. I don't think this could be the sender, since it would max out the gauge at Full mark, right? Can't think of any wires I could have touched under the hood that would do this?
Appreciate any advice, thanks! -Jim.

the problem of the fuel guage pegged past full would indicate an open circuit in the fuel sender circuit.

the sender signal goes to under the fuse box , connector 152. this then routes the signal to the PCM.

remove the fuse box and check these very small wires for damage , also the connectors to the PCM. pin j & k of conn 152 are the sender circuit pins/wires.

on my vehicle the rats chewed connector 152 pin "a" wire that is the 4wd wheel lock circuit.

most likely you stessed out those driverside wires too much around fuse box/pcm.

j cAT, right on the money! I had used a strong bungee cord to keep the large main harness up & out of the way so I could lift the manifold out of there. And since I had opened the clamps which secure that monster of a harness, the lifting force apparently stressed a couple small wires under the fuse box, at Conn 152. repaired them both, now have functional fuel gauge! So happy I went and filled up the tank! Well, I tried to, but the pump shut off at $75.00, (reached the pump's bank card authorization limit). Can't believe that stupidity, can't get more than 20 gallons at a time! And that was the "cheap" gas, "only" $3.59/Gallon!! :mad: :angryfire The gauge now shows just under full. Thank you again!!:)

I have been following you repair progress. since I have not done this repair yet, I did not comment on exactly how to proceed concerning the upper intake removal.

I have had to repair the dam/spacer filler material . the rodents appear to like to chew on this. then water/corrosive deicing chemicals can get in there and mess up the KS.

you would have had a very difficult time finding that problem. I traced out the wiring of the sender to the pcm and being familiar with this under fuse box area it all made sense to me , that this is what occured. having the helms shop manual is what you need to properly troubleshoot these wiring issues.

good luck with your vehicle repair .