Remote Locking Ceased

[onthecut]

Hi Guys.

Title says it all --- the lamp still lights on the fob, but that's it. Is there any simple way to check if the fob is sending -- don't suppose anyone has the proper test tool ?? Failing which, any favourite failure points to check ? It's the radio type, not IR.

Mike.

[Peter.N.]

Hi Mike

Its output frequency is about 330 mhz. If you know a friendly radio ham its in the 70cm band, or you may find a scanner that goes up there.

The fobs tend to suffer from dry joints but you need good eyesight and a very fine tip soldering iron to repair, you can sometimes actually see where a component has parted from the board one end.

I think I still have a 70cms handheld here somewhere, so if all else fails sent it to me.

I have had a couple that dont work and have replaced the fob and reciever from a scrap car.

Peter.

[Dieselman]

Are the later keys RF then.? iirc my earlier cars were IR same as the Xantia, which do fail due to dry joints on the LED.
As I'm sure you're aware, LED IR output can be checked with a digital camera.

[xmexclusive]

Hi All

Mk1 XM's were fitted with single button IR remotes with no deadlocking.
UK Mk2 XM's were fitted with two button dual frequency RF remotes with 2.4M combinations. Not easy to crack or pair up bits. By 2000 this system in a modified form had became the common standard for most cars. The modification changed the functions allocated to the dual function button. There are plenty of very cheap (£20ish) aftermarket sets that follow the common standard. It just needs a bit of wiring and a couple of diodes to alter the kit to work to the Citroen button functions.

John

[JwC]

My remote (2.5TD Exc) has recently failed but central locking from the door is OK still. I plan to investigate. Now I've seen the frequency (on this thread) I can check the fob but I blieve this is a receiver problem as reception got steadily worse before it ceased (and it's not fob batteries). There's a tubular module in the over head unit that used to buzz audibly, but which is now quiet. I suspect deceased. This (Haynes appears to confirm) I assume is the sensor unit. Is this the most likely fault? Replacement looks easy enough? But can I also just swap for another (I assume the decoding is done by a computer in teh background somewhere). Thanks

[xmexclusive]

Hi JwC

Fraid not. Roof light receiver is for Mk1 IR type remotes only.
The noisey little fan up there that has now died is the sensor for the climate control.
The Mk2 RF receiver is found under the passenger side dashboard glove box. Fairly easy to get to unless you have a later car with passenger airbag.
Black box (100x60x30mm) white 9 pin electrical socket.
Will be marked TEXTON 96160582.80
These are part of a set (receiver and 2 plips) that are factory code matched.
As well as the normal remote signals each plip transmits its own set of rotating rolling code numbers. The receiver needs to get both sets of information. To stop anyone with a scanner understanding this code combination while it is being transmitted the plip scrambles it and then the receiver decodes it. Each time the plip is pressed the rolling code moves on to the next number in the sequence. This makes it virtually impossible to decode the transmitted signals even if you keep scanning them.
Because of the rolling codes are unique to each plip and not reprogrammable it is not possible to get the receiver to learn another plip so you cannot make up sets from bits and pieces.

John

This post has been edited by xmexclusive on June 12, 2010 09:47 am

[JwC]

Thanks for the info - very useful. That explains why the climate control is so slow to respond to things! But that would appear easy enough to fix. The remote seems to be another matter. From what you say I need to buy a complete set of parts whether new or s/h and fit those (it's easy enough to swap the electronics into the old key body. I'll have to start looking around.

[xmexclusive]

Hi JwC

A new remote set from Citroen is now close to £300.
Buying just a Plip or a receiver is around £100 each but needs the radio code which is marked on the receiver case (Code elec: Exxxxx). Then unless you still have one working plip you cannot be sure if it is the receiver or the plip that is faulty. If ordering just a plip you have to specify the full radio code for the plip you need (xxxxx.0 or xxxxx.1). There is usually a little paper label with this code stuck on the plip pcb.
The .0 or .1 tells Valeo which of the two sets of rolling codes are required in that plip radio code. Allegedly obtaining and using two plips of the same rolling code locks the system up.

These days most XM owners seeking a replacement system go for the Chinese clone sets obtainable for less than £30. Some wiring and circuitry changes to make them work in an XM but a reasonable price. There are a few write-ups on the various XM sites where members have documented fitting these clone sets.

John

This post has been edited by xmexclusive on June 12, 2010 03:23 pm

[JwC]

Thanks for the info. It's really useful to have access to such well informed specialists. It makes a huge difference to confidence in trying to keep this beast on the road without it costing an absolute fortune! The car seems to be going through a sort of deathwish phase with faults at the moment and whilst none is terminal on its own it is testing my patience and resources. But the vehicle is basically sound and I've no intention of giving in just yet. So I'll be back for more help I'm sure. For example it has jusrt started 'misfiring' once in a while, something that is cleared by restarting. (It's not running MS Windows is it?). But I guess that may just be dirt in the fuel system somewhere (it's clearly not compression problems). Oh well.

[robertmnorton]

Hi Jwc,not to go to far off tangent,if you're getting lots of minor electrical or possible electrical associated gremlins,then battery condition(remember this is related to age as well)charging,ignition switch and under bonnet fuse block are well worth the time in testing.A lot of the ecu's in the xm do not tolerate well dips in supply.The engine and suspension ecu's particularly.
robertm

[JwC]

Hi. A good point. Whilst I'mpretty surethe battery and elctrics are good, I did notice the battery clamp wasn't great. One of those things on the list to do! It will get escaleted to the top! Thanks

[xmexclusive]

Hi JwC

Robert is right about a cautious and logical approach to XM repair.
It is so easy to have a problem, identify a particular solution, do the necessary perhaps at some cost, then find that the problem is still there or reappears.
One fairly positive check would be to try a known good RF remote set in your car while testing your set in the other XM. Quick and easy to do as long as you do not have a passenger airbag in you car dash. If you are anywhere near me then we could perhaps set this up.

John

[noz]

One thing that might be worth trying is to resynchronise the fob with the car. If they have been spearated for a while or the battery in the fob has been flat for a while then the central locking brain can forget which fob it is supposed to be matched to. If thats the case, re-matching the fob to the car is easy.

I don't have a handbook to hand but it goes something like this: Sitting in the car, turn on the ignition and hold the top button on the fob in for 3 seconds. Done.

If someone finds their handbook before me please confirm if I have described the process correctly or not.

If I find mine I'll do the same.

Cheers

noz

[xmexclusive]

Resync of the plip set on an XM Mk2 is a single push on the plip button.
Does not need the ignition on. Holding the button down has no effect.
That is the process by which other Citroens with the lower security (without rolling codes) RF system learn a new plip.
With the XM RF plip the scrambled radio code is always transmitted with each button press. The receiver decodes the signal and checks the sent radio code with its programmed radio code. If the radio codes do not match the plip is ignored and the car stays locked. If the radio codes agree the receiver then moves on and compares rolling code numbers. Only if these agree does the car unlock. If the rolling codes are out of sync then the plip button must be pressed again. With each press the plip moves on to the next rolling code in its sequence while receiver is still looking for the same rolling code number. If plip and receiver are from the same set then after a key press or so the rolling codes will match and the car will unlock. Plip and receiver then move on to the next rolling code and so remain in sync. This is why an XM plip may need more than one press to unlock the car. The rolling codes can drop out of sync if for example you press the plip out of range of the car or if you alternate plips. Not sure if the XM rolling codes are a 2, 3 or 4 number sequence. The higher number the manufacturer choses the greater the security and the greater the uses frustration with the number of button presses to resync. Not helped by Citroen limiting the amount of customer information for the system. Mk2 handbook says "Press the button once. If the central locking fails to operate, press again." That suggests that the XM plip has a 2 number rolling code sequence.

John

[regdorpten]

I'd second xmexclusive's suggestion of buying a £20 aftermarket kit. I fitted one to mine, it's a fairly simple job, there's a few threads on here on how to do it (largely written by xmexclusive) and it works fine. I didn't bother getting the key recut, just use the new plipper as keyring on the old ignition key. I just don't see the point in paying citroen prices for technology that is today dirt cheap. Same with parking sensors, which i fitted for £20.

Of course there is a downside...the plipper sometimes goes back to front and for weeks at a time lock is actually unlock and vice versa, and my parking sensors appear to think heavy rainfall is a brick wall....but hey central locking and parking sensors for less than half the cost of filling the car with petrol....