Fuel Gauge showing full all the time

[Bull183]

hi, I have an 02 tiffan allegra 38' bus on a freightliner chassis, i'm having a hard time fixing my fuel gauge, it hasn't worked since I bought the rv 2 1/2 years ago, everything else works on the dash, the fuel gauge is reading full all the time, I dropped the tank and replaced the sending unit and also replaced the gauge on the dash, the gauge still reads full, it has to be a wiring issue, so tonight I called freightliner to get a wiring diagram and they couldn't find one for the fuel system but told me it sounds like a grounding issue. I called tiffan a couple days ago and they told me to call freightliner, I'm going to try tiffan again tomorrow. I need to check the chassis ground but i'm not sure where to look

[rrtribble]

Easy fix is to go to the tank and run a ground to your chassis from the sending unit. If it is only a ground problem that should correct it.

Richard

[Bull183]

I just ran a wire to the frame for ground from the sending unit and it is still saying full

[rrtribble]

With the new ground in place and the problem continues would indicate that it is not a ground issue so we can move to the next step. My next step would be to check the gauge for voltage coming in and the sending unit for voltage going out. I personally would start with the guage by checking to see if you are getting voltage from the sending unit. Both have been known to be bad when you buy them. If you are getting voltage at gauge it would seem to be the gauge. If no voltage at gauge then it is either a break in the wiring or a bad sending unit. I would take the gauge out and wire it directly to the sending unit by the tank to see if it is working. If not working then it would seem to be a bad sending unit. If it does work right then it is apparently a break in the wire between the sending unit and the gauge.. You can run the line to see if you can locate it but I suspect there will be several feet where you will be unable to inspect the lines. Check what you can and repair what you find. If you can't locate a break I would run a new line from the dash gauge to the sending unit.

Hope this helps - Richard

[Skip426]

There's a section in this pdf for testing the fuel gauge.

Check the date on the pdf against your chassis production date as , F/L changed the whole gauge package around 02/03

I do have wiring diagrams & schematics for my 99 side radiator F/L chassis , but they may not cover your newer chassis .
The schematics show the fuel sender ground wiring ( G-1 ) going through several splices and attached to a chassis ground stud . That stud on my coach is behind the left head light in front of the steering column.

[Bull183]

thanks, I actually called freightliner and talked to a service guy there, he sent me the troubleshooting guide and schematics. I spent last night narrowing it down to the message center, it looks like that is the problem. i'm going to call now to get a price, and also try to find a used on