Speed Sensor! XUD 605 DT

Adstar · Post by **Adstar** » 22 Jun 2006, 13:09

I have just narrowly passed my MOT with a VERY intermittant speedo. I don't want to have the same problem in 12 months time, so I am starting the reseach now inorder to get a fix in place by the end of the summer.

I believe that it is an electrical feed from the speedo into the EMU/ECU. My mechanic disconnected it and couldn't see any obvious faults, so reconnected it. In this process he has obviously moved the bit of dirt that was causing the problem, and made it worse!

So:
1) Can anyone give me anyinfo on the way the speed sensor works?

2) Does anyone know what else had the gearbox I am using? If I want to extract a replacement from somethign I might have better luck looking for something less rare than a late model 605!

3) Is there any mechanical device involved in the speed measurement and recording?

Thanks

wheeler · Post by **wheeler** » 22 Jun 2006, 18:40

The speedo isnt checked as part of the MOT test so i dont know how it narrowly passed.

Adstar · Post by **Adstar** » 26 Jun 2006, 09:02

I can't find anything to prove you wrong! I am in stunned disbelief. Whats more your not the only person to have said this.

So, it has actually breezed through the test requiring only a couple of bulbs and gaiters to be fitted.

This does not however answer my question. I still need to know about how the speed is measured and what little boxes of black magic etc are used.

jgra1 · Post by **jgra1** » 26 Jun 2006, 14:26

I agree with wheeler.. never had a speedo check for MOT.
(the only time whern they may do this is when they test drive the vehicle, which some places do during an MOT... I also guess they could prove a faulty speedo on the brake rollers?)

My Xantia suffered a speedo fault once after I replaced the clutch. The mechanism is something like this. Speedo Drive housing bolts to side of diff. Inside this metal case, RH driveshaft goes through a large plastic housing, this turns, and has a toothed ring at one end. This toothed ring turns a metal shaft via 90 degree worm drive. This metal shaft goes into, and turns the speed sender. From then on its electrical.

My suggestion, if yours is a similar set up, would be to remove the sender itself, and get a cordless drill with a square section bit, and just see if that reads anything on the speedo. If it does then you mave have mechanical failure, if it doesn't then I would suspect the speedo head itself. On ine, the re-entry of the drive shaft destroyed the plastic turny bit

good luck, John

fastandfurryous · Post by **fastandfurryous** » 26 Jun 2006, 21:16

did the tester say that it had "only just" passed due to the speedo not working? or was that your own opinion?

There are a multitude of things that aren't checked at MOT time, the speedo being one of them.

Other common things that people believe are checked are things like Rear wipers, heated rear windows, front fog lamps, front driving lamps, engine/gearbox/clutch condition, etc etc.

a car can actually be in fairly bad condition and still pass it's MOT.

PowerLee · Post by **PowerLee** » 26 Jun 2006, 22:24

Working speedo isnt part of the MOT test.

Only thing that might happen in the future if the speedo is dead & mileage isnt going up is an advisory.

With the computer based MOT tests the mileage will get picked up at the second test as not changed from the first test & may earn you an advisory ( which also gets put on the computer )

Adstar · Post by **Adstar** » 27 Jun 2006, 08:49

The speedo isn't dead. Just very selective about the times it works! So te millage will go up between tests.

Does anyone know how the speed is detected, and sent to the speedo?

I have the MOT and I know a lot of things that aren't checked, but I still want to attempt or research into solving my speedo problem, for obvious camera related issues. I need something more accurate and instantly measurable than my knowledge of the rev counter!

wheeler · Post by **wheeler** » 27 Jun 2006, 18:14

never even seen a 605 but i assume it works the same way as other peugeots/citroens.the sensor in the diff is a hall efect sensor that gives off a square wave signal the frequency of which depends on the speed that it is turned at by the plastic gear on the driveshaft.the plug has 3 wires, 1 ignition feed,1 earth & one is the signal wire that goes to the instrument panel.

AndersDK · Post by **AndersDK** » 28 Jun 2006, 01:20

wheeler wrote:never even seen a 605 but i assume it works the same way as other peugeots/citroens.the sensor in the diff is a hall efect sensor that gives off a square wave signal the frequency of which depends on the speed that it is turned at by the plastic gear on the driveshaft.the plug has 3 wires, 1 ignition feed,1 earth & one is the signal wire that goes to the instrument panel.

Add to this that the speed sensor is located the same place as where you expect to find the good old speedo cable attached - on the diff top RHS.
On Xantias the sensor plug is prone to get dirty/corroded and then fails to indicate on the head unit.
Note that both sender unit plug pins - and the cable connector mating pins can be at fault.

I admit its not the easiest place in the world to access for cleaning some electric plugs - but it will be necessary to exclude this very common problem.
Once plugs are cleaned and refitted - spray with a silicone spary - NOT WD40.

Adstar · Post by **Adstar** » 28 Jun 2006, 08:35

Brilliant. Thank you very much, finally a definative answer! At least now I can have a plan of action.. Take off the unit, clean up the sensor, clean up all the plugs.. spray, with silicon, and refit the unit.. cross fingers.

Your description of the dirty connectors does make sense and would fit the symptoms.

What I have been more worried about is the number of people that keep referring to the speedo cable! I couldn't work out why I would have 2 forms of 'sending system'. Besides which, a mechanic system woul require the gearbox to be removed in order to replace the little plastic cogs.

My mechanic described the box 2 me. It sounds like I need a day under the car, but it also sounds like it shoulnd't be impossible to do a quick clean up operation.

Thanks again.

jgra1 · Post by **jgra1** » 28 Jun 2006, 12:28

Adstar, working under car on ramps, your sender will be held by (usually) a 6mm allen bolt, there may also be a shield present...

You can get the sender off the car (test as per my earlier posting) clean and refit in 20 mins

let us know

Adstar · Post by **Adstar** » 29 Jun 2006, 08:32

Not allen bolts.. I HATE them! I suffer them on the Formula Ford! I think now is the time to buy some allen sockets rather than just the keys!

Thanks for the advice. I might not get the work done for a while, but I will update this thread with my results.

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Speed Sensor! XUD 605 DT

Speed Sensor! XUD 605 DT

Trying to get the thread back on track!