405TD - fuel gauge stopped working!

r.welfare · Post by **r.welfare** » 06 Jun 2008, 17:45

Just gone out to the shops in my '93 405 Hunter TD estate, and the fuel gauge resolutely refuses to move from it's resting place, well below "empty". There is definitely at least 2/3 of a tank in it...

It's the type of instrument cluster that has the fuel gauge between the revcounter and speedometer. I will go and top up the tank at the filling station later to see if this cures it - thumping the top of the dash has had no effect so far - are these prone to failure, and if so is it likely to be the gauge itself or the sender unit, which I assume is in the tank somewhere?

AndersDK · Post by **AndersDK** » 06 Jun 2008, 18:04

As with most PSA cars, you should have an access cover under the rear seat. Here you can inspect the 3-lead cable and connector from the tank sender - if its is corroded or have dislodged.

I'd say that the sender wire itself may be shortcircuited to earth, or the gauge is disrupted in the dash itself. If the sender (or wire) was simply disconnected - the gauge would read a constant false high.

The gauge is connected via the 3-lead cable running to the fusebox - and from here via the many interconnections between fusebox and dashboard.

r.welfare · Post by **r.welfare** » 07 Jun 2008, 18:17

Thanks Anders. I'll have a poke around under the rear seat first. Oddly enough, it began working again last night and all this morning - then refused to "get out of bed" again when I moved the car this afternoon. So maybe a heat-related issue - it has only been doing it so far when the ambient temperature has been hot?

Just also discovered that the estate has a 140mph speedometer as well, whereas the saloon has a 130mph one - not that a 405TD could get near those speeds anyway

evilally · Post by **evilally** » 08 Jun 2008, 18:27

Sorry, don't mean to hijack

but I also have trouble with the fuel gauge on my 405. When full, it reads full. When empty, it reads about 3/4 full. It goes all the way to 0 when the ignition is off. Interestingly, the orange fuel light comes on when it is down to 10 litres or so. I've checked the wiring on the sender unit and it seems fine, which makes me think the gauge itself is faulty?

AndersDK · Post by **AndersDK** » 08 Jun 2008, 18:42

The tank sender unit is a very simple resistor element on which a slider is pushed up/down by a float.
Since your low level warning lamp is working, the float is also working as it is the float that makes a contact when it comes near the tank bottom.

Have a go like the desciption above, looking for any weak connections, as any added resistance from corrosion will show as a higher tank gauge reading.

You may have success trying to clean the sender unit resistor element, but they really are delicate units.