Electronic Speedometer Not Working

Hi all,

My new acquisition has an electronic speedo which was reported as intermittent but which has not worked at all since I bought the car. There is also no mileage increment, neither trip nor total.

There is no readout on the computer display of instantaneous fuel consumption, average fuel consumption or average speed.

Am I right in assuming that this points to a fault in either the transponder (fitted to the autobox) or its associated wiring, rather than the speedo head?

If that is so, can any of you suggest the best way of testing/isolating the faulty component? I've been underneath and disconnected the plug at the transponder but that's the limit of my knowledge.

Grateful thanks as always.

Derek

Hi Derek,

Your diagnosis is correct. It will be the sensor or its associated wiring to blame. There's a joint in the cable coming from the sensor and it takes the form of a white coloured connector. Its located down by the side of the LHM reservoir. It takes a bit of fishing to get a hold of it but once you can grab it there's enough slack to be able to pull it in to view. The connector can then be split and the cables tested in both directions.

To let you understand the signal coming from the sensor splits after the white connector and goes to two places. One connects to the speedo in the dash via the engine ecu and the other connects to the ecu which controls the suspension. Therefore the absence of the speed reading will also cause problems for your hydractive control too.

The sensor itself is a pig to get to. I haven't heard of anyone successfully attempting to remove it but thats not to say it cant be done. I think I'd exhaust all electrical tests including an oscilloscope before trying to remove it. You may even find that its a break in a cable or a dirty contact in the connector.

Best of luck.

Cheers

noz

Thank you Noz,.

This afternoon I ran the car up on ramps and slid underneath. On the 2.0 turbo the sensor was remarkably easy to remove from the diff.casing. I've checked the first length of cable for continuity, the next step is to have the sensor checked and then it's dash removal time.

When in there I'll take the opportunity to change all the bulbs that can be changed and maybe try my luck at restoring the missing vertical lines on the LH dot matrix display. I seem to remember something about restoring tracks with a soft lead pencil but can find nothing now.

Derek

Come to think of it, restoring tracks with a soft lead pencil was probably something to do with speeding up an Athlon CPU!

Derek

Derek, here is a link to the pencil-repair:
http://www.tramontana.co.hu/citroen/electr...ric.php#Display

I myself chose a different way, explained here:
http://perso.orange.fr/alain.mionnet/xmdisp.htm
I've made an English translation if your French is a bit rusty

Hi Jan-hendrik,

Thank you very much for the repair processes on the dot matrix display.

It was 58 years ago last month that I failed my matriculation French with a miserable 12%, so now it's as rusty as a GS door bottom.

Cheers,

Derek

This post has been edited by DerekW on June 17, 2007 11:36 pm

Further to the speedo saga, I removed the drive pinion and shaft assembly from the sender unit and the first thing I saw was a band of heavy corrosion on the outer surface of the shaft, over the last 12mm above the bearing surface.

The shaft must have acted like a cork in a bottle, because the next thing was that I had a hand full of clear fluid that turned out to be water. Much shaking later and I managed to empty the sensor/transponder of its liquid contents.

Discounting the possibility of Citroen using water cooling for the transponder - quick on the uptake, me! - I don't think that water and electricity go well together and it looks as if I've found the problem.

I've ordered a new transponder (£68.72 with VAT, Ouch!) but looking at the design, the internal shaft goes right through to the top where it emerges in the bottom of a cup, obviously a leftover from the cable drive. This forms a nice little reservoir to feed water down the hole in the centre of the shaft. When I fit the new one I think I'll seal that cup with bathroom sealer or something similar.

Derek

Further to the speed sensor saga; the £68.72 sensor had only two terminals instead of the three required so that was no good.

A more expensive one, £89.40, looked to be the same as my old one but the internal shaft extended too far so that the pinion shaft would not go fully home.

Only one other type left, the gear went fully in and best of all it was a shade under £40. It had an extra locating spine for the plug, but the plug on my car had a slot to mate up with it. Citroen have changed the design so that the top is now fully enclosed so I won't need the bath sealant. Took it home, plugged the cable in, turned on the ignition and rotated it with an electric drill - 30mph said the wife. YaHay!
Here endeth this posting.

Derek

Happy for you Derek! From your postings, it seems your dealer had the various transponders quickly available, is it true? My upper speedo cable (not electronic like yours) is "ticking" 2 years now but hasn't failed yet!

regards
George

Hi George,

They had to order the middle priced one, weren't too happy when I showed it was the wrong one. The other two were in stock. I also asked the price of a new LH dot matrix display - £425!

Had a look at the C6; they don't even have it inside the showroom, parked outside with the cheap cars with the front number plate (with "C6" on it) hanging down from a single screw. It probably drives and rides like a dream but to my eyes it lacks presence and certainly doesn't look like a £35,000 car.

Derek

I thought it was called a transducer

I thought it was called a transducer

Hehe, don't really know, you native speakers decide and let me know!

G


BTW my dictionnary says:

transducer:
An electrical device that converts one form of energy into another.

transponder:
Electrical device designed to receive a specific signal and automatically transmit a specific reply.

Yeah, I agree they missed it on the front part, not distinct enough, shame -probably on the "facelift" they'll make it look like it should have, like it hapenned with the C5-; I find the rear quite a success though. I also think there's a problem with the colors choice; why do they show all the time this dull grey-ish, on most adverts? Aaaaanyway...
G