Xsara fuel gauge problems - is this a common fault?

uhn113x · Unread post by **uhn113x** » 22 Aug 2010, 13:33

Hi folks

A few folks have suggested this is a stock fault, but nobody has come up with a definite answer at all.

Car:
March 2001 Xsara 2.0 HDi - not multiplexed wiring AFAIK, but no idea how to check this!

Fault:
Fuel gauge either works correctly or is about 1/4 too low; when this happens it seems to stay like it until next used.

As there's no Haynes manual for the later Xsara, I cannot see how it's all wired and therefore what to check.

I don't want to start replacing things ad hoc until it's cured - I'll leave that sort of thing to the dealers. I am fine with electronics, BTW.

Any ideas, folks?

Unread post by **RichardW** » 22 Aug 2010, 13:43

If it's a pre-faclift Xsara (ie with the small head lamps) then it is not multiplexed. If it's got the big headlights, then it will be.

Does the odometer continue to read the correct distance travelled when the speedo is playing up? If it does then you can rule out the speed sensor, if it doesn't then it's probably the speed sensor. If you think it is not the speed sensor then it is most likely the pins where the speedo head is soldered onto the instrument panel PCB. This makes the speedo reading erratic - often hanging at 50 regardless of actual speed. The one in my Xantia reads what it likes most of the time, and can swing from actual speed to 50 and back at will. I just ignore it and use the tacho instead - maybe one day I'll get it out and solder it up, but then I've been saying that for 60k miles now, so maybe not!

uhn113x · Unread post by **uhn113x** » 22 Aug 2010, 14:20

Apologies, Richard, and a d'oh moment!

I said "speedo" for some strange reason whereas I should have said "fuel gauge".

Crawling back under my stone!

It is multiplexed, then

. Is there a wiring diagram avaliable at all, without spending a fortune, as I'm a complete newbie regarding these things.

wheeler · Unread post by **wheeler** » 22 Aug 2010, 21:08

RichardW wrote:If it's a pre-faclift Xsara (ie with the small head lamps) then it is not multiplexed.

Thats not quite right the late ph1 xsaras were multiplexed also.
As far as the fuel gauge goes im afraid this is a quirk of the xsara, if you replace every component involved in the circuit it will still operate the same. The gauge takes an initial reading off the sender in the tank then the ECU calculates a theoretical usage & adjusts the gauge, needless to say it doesent always tally up with the sender reading hence why you get erratic readings.

uhn113x · Unread post by **uhn113x** » 23 Aug 2010, 08:21

Thanks, wheeler, that's finally answered my question.

That sounds like a typical bit of "progress" - if it ain't broke, it's too simple, so we'll get the design team to find a complex solution that will never work properly!

What was wrong with a bit of wire and a rheostat, one asks?

Clogzz · Unread post by **Clogzz** » 23 Aug 2010, 13:38

Hi Mike,

It still has a bit of wire and rheostat, but that’s the only good news.
The best chance would be dry joints at the rear of the gauge.
Picture from the Xantia Mk I, hoping it’s not too different.

uhn113x · Unread post by **uhn113x** » 24 Aug 2010, 09:00

Thanks, they sure look like a few good DJ's!

From what wheeler says about how it works, though, I might just leave it at that and live with it.

I'd love to see some sort of diagram / explanation on this multiplexed wiring, though.
I'm not a complete duffer on the subject as I used to repair, write books and teach TV / radio / video in a previous life.

wheeler · Unread post by **wheeler** » 24 Aug 2010, 17:42

if you ever sort it out be sure & let the rest of the world know how.

uhn113x · Unread post by **uhn113x** » 25 Aug 2010, 07:47

Ah, but from what you said above, it's a design fault and they all do it.

I think the only solution would be to redesign it, and there aren't enough hours in the day for that; retirement takes up all my 25 hours of each 8 day week!

However, if someone had a sender and gauge from a scrappy, it would be tempting to see what happened if I started to go back to a simple solution ... any offers?

Unread post by **Paul-R** » 29 Aug 2010, 18:34

wheeler wrote:The gauge takes an initial reading off the sender in the tank then the ECU calculates a theoretical usage & adjusts the gauge, needless to say it doesent always tally up with the sender reading hence why you get erratic readings.

That's not the way my Xsara behaves so I suspect it's age dependant.

On the 2001 Xsara it's very much like cars used to be.

After a filling to the brim there's quite a delay before the needle moves off the full mark. This then becomes a benchmark to me of how the consumption is going for this tankful. 80 miles is not good, 100 miles is good and anything more than that is exceptional. The 3/4 mark should be reached when about 180 - 220 miles has been covered and by 1/2 way I need to have covered 300 miles in order to be averaging around 50mpg.

The C5 behaves exactly as Wheeler says and it's crap. I really hate it and I wish that I could change whetever it is in the ECU so that the reading is passed on from the TSU straight to the gauge. It's ridiculous that a so-called improvement should be such a negative move. A triumph of "we can do do it so let's" I think.

If it ain't broke, don't fix it.

Unread post by **myglaren** » 29 Aug 2010, 18:51

Paul-R wrote: The C5 behaves exactly as Wheeler says and it's crap. I really hate it and I wish that I could change whetever it is in the ECU so that the reading is passed on from the TSU straight to the gauge. It's ridiculous that a so-called improvement should be such a negative move. A triumph of "we can do do it so let's" I think.

If it ain't broke, don't fix it.

I have never had any problems with my fuel gauge but I always brim it when the low fuel warning appears, rather than incremental fills more frequently.
Probably will now, of course

Unread post by **Paul-R** » 29 Aug 2010, 18:59

myglaren wrote:..I always brim it when the low fuel warning appears, rather than incremental fills more frequently...

And that's another thing I hate about the C5 fuel gauge - it just completely ignores a 5 litre top-up from the spare fuel can if the light has just come on. On the Xsara it'll go out as it should.

I really would like to shake the designer of this "feature" until his tooth fillings rattle.

Unread post by **myglaren** » 29 Aug 2010, 19:31

You wouldn't have liked a Renault 11 TXE Electronic then