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Fuel Gauge - diagnosis


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As of a week ago, on start up my 300tdi fuel gauge is reading nowt. Even with a full tank and continues to do so.

The engine has just been swapped and the thermostat doesn't work (the wrong sender I think).

What's the best way of diagnosing the fault? (I'm not really concerned with the thermostat, but the fuel gauge is a flaming nuisance!)

I've looked at the fuses and besides being a little corroded they are all solid.

One more weird thing, they all seem to be 5 amps more than it says on the handy guide on the back of the fuse box cover...

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You would need to check the wiring diagrams, but I would remove the wires at the sender end and short them together (or have a very small resistance between them)? to see what happens on the gauge. That would tell you if the wiring for to aft was intact. If that doesn't work it would indicate the problem is between the sender and gauge.

Cheers

Peter

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Those gauges are fed via fuse 3, 15amp, as is also (and bizarrely) the indicators(but not when hazards) and rear wash wipe. Does the wiper work? I have had problems in the past with the rear wiper motor blowing fuses and taking out those items.

Hmm, when you say take out, do you mean the gauge gets knackered too?

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Right, just had a look.

The fuse is definitely okay although it is 20A not 15A???

You would need to check the wiring diagrams, but I would remove the wires at the sender end and short them together

I've done this, nothing happens at the gauge.

What's the next step? Can I apply power directly to the gauge? Should I check for continuity along the wire? Just to double check what resistance should I be getting from the sender (tank full)?

Ta,

Mike

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what wires are on the back of the gauge ?


Green going to a female spade terminal & green with black stripe going to male spade terminal... I ran a multimeter over then and they are reading 11.5v which I'm guessing (and it is a guess) means the gauge is duff...

Do they just pop like this? No reading, no warning?

Cheers,

Mike
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plain green is the 12v ign controlled feed should be on the terminal marked +ve

green/black is the signal from the sender to fuel gauge

plain black is earth

you could swap the temp gauge & see if that reads the fuel contents, it won't hurt the gauge.

i'll give that a go, thanks!

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you could swap the temp gauge & see if that reads the fuel contents, it won't hurt the gauge.

Tried that, definitely the gauge, the temp one rose like it should (nearly off the end of the scale to be fair, a rare full tank!).

Checked the continuity on the earth, measured the (just under) 12v off the ignition controlled feed.

So next questions. What gauge do I need?

Cheers,

Mike

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