300 Tdi Disco - Low Fuel Light coming on randomly

[henrycrabbe]

Hi, Just as the title says ^^^

On my '96 300tdi, the bright yellow "Low Fuel Level" warning light on the fuel gauge is coming on at odd times. It's ok in the daytime because you can ignore it, but at night its damn bright and VERY distracting! It comes on mostly when the gauge reads half full or about a quarter full (dunno above that, I can't afford that much diesel in one go ). Otherwise the gauge itself seems to behave correctly. Has anyone any idea where this light takes its feed from and/or how to fix it without just taking the bulb out?

Cheers,

Steve.

[Wildchris]

I have had this before on one of my defenders. I put a new sender unit in and it fixed it. maybe try and clean the connection terminals to the tank?

[cipx2]

When the fuel light comes one, roughly how much time it stays on and what happens to the gauge needle while the light stays on?

[axlechorus]

Does it come on after a tight long bend or up/down hills? My 200tdi does this sometimes when the tank is around 1/3 full as the sensor is in one corner of the tank and the fuel is being pushed to the otherside as the car corners or ascends/decends the hill. Normally stays on for around 20 to 30 seconds afterwhich is goes out.

Cheers

Ryck

[gripper]

if it works the same way as a series sender with low fuel light does then it will have it's own wire that goes to the sender along with the one for the guage, there is a seperate switch within the sender unit that earths out when the level gets below a certain amount and unless you fancy disecting the sender then replacement is the only remedy.

[henrycrabbe]

Cheers guys,

In answer to your questions:

When the light comes on, it stays on. It will only go out when the ignition is turned off and back on again!

There is no reaction on the fuel gauge when the light comes on, it doesn't jump or anything

It doesn't have to be hard cornering or acceleration for it to come on, in fact one time I remember driving VERY gently to try and prevent it but I failed.

I'll have a look at the sender connections next I think.

Steve.

[cipx2]

Seems to be an intermittent issue. Most likely an imperfect contact at the sender (internal or at the plug), its connection to ground or along the line to the gauge (the line includes 5 connectors - plenty to go wrong).

if it works the same way as a series sender with low fuel light does then it will have it's own wire that goes to the sender along with the one for the guage, there is a seperate switch within the sender unit that earths out when the level gets below a certain amount and unless you fancy disecting the sender then replacement is the only remedy.

It's not like the Series sender. It doesn't have a separate circuit/switch for the low fuel warning light.

The sender has only the variable resistor connected to 2 devices: the fuel gauge and the warning light electronic circuit.

The light is turned on by this separate electronic circuit when the resistance is beyond a certain value for more than 3 seconds.

Could be the above circuit at fault as well but less likely.

[henrycrabbe]

Thanks cipx2,

I got my RAVE disk going and managed to find this:

Low Fuel Warning Indicator

When the fuel gauge sender’s resistance falls below

approximately 25 Ohms (6 liters/1.5 US gallons), the

Low Fuel Warning Indicator will illuminate to warn

the driver.

Apparently there is an "anti-slosh control" built into the circuit in the cluster, I'll have to take the instruments apart and have a look. I'll put it on the list of things to do, somewhere near fixing the electric window ECU and getting the rear screen washer to work! (I daren't even think about the spider module yet )

Steve.