Xantia Speedo Calibration

pete_wood_uk · Post by **pete_wood_uk** » 08 Dec 2004, 18:21

I'm almost certain that the answer to the question I'm about to ask is "No, it's designed NOT to be fiddled with" but I'll ask anyway.
I recently timed my 2000-model Xantia (with the LCD odometer) against the kilometer posts on the motorway and found that the speedo is running about 9% fast (didn't go far enough to check the odometer). It's damned annoying - apart from anything else, it frightens the mother-in-law who thinks I'm driving like even more of an idiot than I actually am [:D]
Is there anything I can do about this (apart from fit bigger tyres [:)]) or am I stuck with it? I became suspicious when driving at an indicated 80-85mph on the M25 and lots more stuff than usual was coming past me...
Cheers
Pete

Kowalski · Post by **Kowalski** » 08 Dec 2004, 19:32

If you get a dodgy sensor or a wiring fault, will that stop some pulses from the sensor being picked up by the speedo and thus the under reading? On the back of the gearbox on top of the diff is a plug, you could try unplugging it, WD40ing it and putting it back together, see if that makes any difference.

NiSk · Post by **NiSk** » 08 Dec 2004, 21:07

I have absolutely no idea if this information can be applied to a Citroën Xantia or not, but I was recently involved in producing a service bulletin for Volvo cars, which described how one changes the coefficient in the speedo circuit for a V50 (which also has an electric speedo) to accomodate different Wheel/Tyre sizes. The change was naturally performed via the diagnostic socket. Is there anyone out there who knows how complex and/or flexible the dispaly systems on Citroëns are? Could be due to the CAN-bus technology being used and I'm not sure if teh Xantia ever got that, but then again, not many car manufacturers make their own instruments, and that means that there may be some redundant functions available (i.e. cruise control on late cars).
//NiSk

rory_perrett · Post by **rory_perrett** » 08 Dec 2004, 21:38

Not much help - but related. My 98 model 2.1TD clocks my trip to work at 26.7 miles. Had a Rover 75 hire car last week which clocked it at 24.7 much to my supprise. Conclusion my odometer is reading 8.1% over. I'm assuming that the speedo is reading a similar amount over as well. May be inherent in the system.
Rory

David W · Post by **David W** » 08 Dec 2004, 22:06

This has been known with Xantias from their introduction...some folks were led to conclude it made them seem to cruise at speed better than they really did...and enhance their apparent fuel consumption.
My own 1993 Xantia will show the highest speed of any car I drive without triggering our village interactive 30mph sign when carrying out calibration trials (!?).
David

pete_wood_uk · Post by **pete_wood_uk** » 08 Dec 2004, 22:18

I must admit I've never calibrated my older Xantia, but the new one does seem to be significantly faster round bends

. It undoubtedly is (better rubber and hydractive) but probably not *that* much faster, so I suspect that this new one overreads by significantly more than my old one. Oh well, "it just does that, squire" obviously seems to be the conclusion

.
Thanks
Pete

nick · Post by **nick** » 08 Dec 2004, 22:30

The speedos in post 98 facelift Xantias were worse in this respect than those in the old shape cars, or so I’ve been told.

JohnD · Post by **JohnD** » 08 Dec 2004, 23:22

My present Xantia 2.1 Estate, and also my previous BXTZD both register 5% more miles than I think they should.
Many times I've driven from Calais to Malaga which GPS states the distance as 1289 miles. I always record around 1350 miles. If the car really does over state the miles, I dread to think what the actual mpg is!

wheeler · Post by **wheeler** » 08 Dec 2004, 23:36

i do know that a non-muliplexed Xsara can be calibrated,having been in a xsara police car (for legitamate reasons,honest) i noticed that it had a calibration sticker on the speedo head.i have no idea how they do it but im pretty sure it wont be through the diag socket on a non-multiplex car.i would imagine that any electronic speedo can be calibrated.

AndersDK · Post by **AndersDK** » 08 Dec 2004, 23:45

My late father in law had a light-blue Lloyd Alexander TS (0.6L engine), in which he had a sticker on the dash telling :
"when your meter shows XX"
"you are driving YY"
Now that's calibrating [:D]

RichG · Post by **RichG** » 09 Dec 2004, 00:40

I have a hand held GPS which I use attached to the winscreen and linked to my PDA for basic sat-nav. The GPS speed indicator, which is said to be + or - 0.5 mph indicates, on a straight road, that my speedo reads correct at 30 mph and about 1 mph fast at 70 mph. As a comparison my wife's Micra reads 2.5 mph fast at 30 mph.
Richard

petefa · Post by **petefa** » 09 Dec 2004, 02:51

Simple thought, but have you tried following a friend, who had a mobile phone(hands free of course![:p])and get him to drive at a set speed and see if your speedo is matching theirs?

Panjandrum · Post by **Panjandrum** » 09 Dec 2004, 03:07

"I became suspicious when driving at an indicated 80-85mph on the M25 and lots more stuff than usual was coming past me..."
Possibly off the point, but could you have been going clcockwise on the anticlockwise lane?
PJ

dnsey · Post by **dnsey** » 09 Dec 2004, 03:30

Undoubtedly that your speedo can be calibrated, but you will need a pulse generator with calibrated frequency counter to do so.
It's not really viable to drive with the instrument panel hanging off and a screwdriver in the back whilst watching the reading and keeping a constant distance from a timing vehicle[:o)]

Stempy · Post by **Stempy** » 09 Dec 2004, 04:34

Not sure about the Xantia speedo but I recalibrated the speedo on my motorbike which uses a similar electronic pick up. I firstly bought one of those bicycle speed computers which can be accurately calibrated to 1mm of wheel circumference. Should be as easy to fit to a car as to a bike. Having fitted this I noted the difference in readings, which turned out to be around 10% across the range. I believe this is built in inaccuracy so the manufacturers can't get blamed for drivers speeding. I then removed the speedo and fed the pulser input with a fixed frequency. On the rear of the speedo circuit board were a number of jumper wires and I found that removing each one in turn made the speedo read differently for the same input frequency, so I just kept changing them until I got a reading 10% below the original reading and on refitting found that the bicycle computer and speedo tallyed perfectly at all speeds. (The bicycle computer I used goes up to 183mph!).