Fuel Gauge Voltage Range

Does anyone know what voltage range the 300tdi Fuel Gauge works over?

Mine is constantly reading Full, so ive got it out on the bench supply and want to move up and down the voltage range to heck the gauge before digging the sender unit out.

Full voltage will be full tank, although this may be regulated before it hits the gauge, but I can't remember seeing a voltage stabiliser when I did my bulkhead so I don’t think it is.

Anyway, apply 10volts to it and it will either show full, or about full, if it shows about full then it’s got a built in voltage stabiliser in which case you can give it from 0v – 14.4v happily.

If it’s always showing full then it is almost certainly because the wiring is touching somewhere or the sender in the tank is goosed.

Ok, So

0v is empty
and 10v is Full

So if i wind the voltage from 0v to 10V the gauge should creep up in turn with the voltage

Yeah - you will certainly be able to work out if it's working or not.

Ok.
10v gives me just over full
6v-8v is just below full
and then the gauge falls with voltage, i.e 2v is 1/4
4.5v 1/2
5.5v 3/4

I assume this is correct and therefore the gauge is fine and in fact its most likely the Sender that is foo bared.

yep, gauge seems to be working just fine - so either sender or wiring Sam

Cool.

If i put a meter across the two wires that I've disconnected from the gauge I'm getting constant 12.2v.

is this leaning more towards the sender unit?

If a fuse had blown would i get 0v, and therefore nothing on the gauge, as someone at work suggested a blown fuse may cause it read max permanently but i cant see how.

Silly quesion - any idea how much fuel in your tank?

A blown fuse would as you say give no reading at all

Assuming tank not full, suspicion is that the resistive coil in the sender that varies the voltage was the float moves has failed, allowing straight pass through of 12v

Silly quesion - any idea how much fuel in your tank?

A blown fuse would as you say give no reading at all

Assuming tank not full, suspicion is that the resistive coil in the sender that varies the voltage was the float moves has failed, allowing straight pass through of 12v

I'd quickly lift the sender out (think yours is a 90, so easy to get at under drivers seat) and see if moving float by hand alters voltage - but from your description pretty sure it is the sender

Its just over half a tank.

Looks like ill whip the sender out, check with meter by moving float up and down.
and then buy a new one

Yes tis a 90

At the tank end disconnect sender plug and bridge the two small connectors,the gauge should show full.If ok,remove sender from tank and bridge connections with an ohmmeter.Moving the float lever through its complete arc,should read 15 ohms at 'Full' through to 245ohms at 'Empty"["Half" is 64ohms]Fuel light 'On' at 158ohms.Mine had a bad soldered joint on the braided copper wire that runs through the float lever,so worth checking connections.If completely stuffed new one is part no ESR1223. This is assuming same parts as on a 300TDI Discovery??