Folks,

Occasionally, despite fresh batteries, my locking remote "plip" fails to work.

Normally, we can access using the key, reset the plip using the "ignition on - button held" method, and all is well.

This morning, the plip failed, and the key rotated in the lock without activation. Help!

Eventually, I pressed the tail gate button in whilst rotating the key, and this worked, and I was able to release the door buttons. However, I am aware that occasionally, in the past, the tailgate button has rotated, too. hence there is a real possibility of a total lock-out.

As the fault is probably with the car-based equipment, is there anything fixable on it, such as an on-board battery? Am I right in thinking that the plip and the car received are a matched unit?

Is there any other solution if this happens again?

r

You will probably find that the plip has a 'dry joint' that's one that appears OK but isn't making contact. Examine the circuit board closely with a magnifying glass and look for cracks. If yours is an early XM with infra red, check the LED on the board, the solder can crack round its connections.

Peter

Thanks, Peter.

I did look at both of my plips a few months ago, but found nothing. i now have a better magnifying tool, so may take another look.

I tried the second one this morning, and had no result with that either. I take it that the red light showing when the button is pressed is not a true sign of serviceability?

I'm suspecting something on the car, but don't exactly know what.

r

..............the key rotated in the lock without activation..................
Am I correct in my understanding that on some Citroen models with IR locking e.g. Xantia II and XM I (both of which I have owned) the driver's door KEY does not always engage (to open the door) unless the button is also pushed in at the same time?

..............the key rotated in the lock without activation..................
Am I correct in my understanding that on some Citroen models with IR locking e.g. Xantia II and XM I (both of which I have owned) the driver's door KEY does not always engage (to open the door) unless the button is also pushed in at the same time?

Ah! This worked on the tail gate, but I can't recall trying it on the main doors. You may well be right.

However, I do recall situations where the plip has not worked but the lock has worked (not spun).

I'd be amazed if there was not some kind of "get out of jail free" option in the even of failed central locking. But, in over ten years of XM ownership, I've often been amazed...

If the locks are worn you sometimes need to push the key hard into the lock to get it to engage.

If yours is an RF plip you can check for an output using a scanner or amateur 70cm radio, I think the signal is at about 330 mhz

Peter

Key rotation is a sign of mechanical missmatch between key and lock.
Nothing to do with the electrics at all.
It is an additional security feature built into the design.
Engineering wise it is a rather clever design.
In practice it has some reliability problems.
One set of 4 tumblers is mounted in the main lock carriage.
These operate off the 4 kerfs cut in the narrow side of the key.
Sum of kerf depth and tumbler length needs to match the radius of the lock cylinder.
In a normal medium to low security house door lock a single row key/kerf match is all you need to turn the lock.
In the XM door lock no narrow side match and the lock barrel just spins.
If the key and tumblers do have a narrow side match then this releases the centre slide.
This centre slide has another set of 5 tumblers set at right angles to the set of 4.
These 5 tumblers operate off the 5 kerfs cut in the wide side of the key.
Sum of kerf depth and tumbler length again need to match the radius of the lock cylinder.
Only now is the centre slide free to slide further into the lock against a spring.
The back end of the slide has a projection that fits into a similar shaped slot in the main lock body and operates the lock.

As the locks age with use wear on the kerfs and lock tumblers can make a particular key a bit iffy.
Locksmith cut keys are always a bit suspect because of the accuracy of cutting and the wear state of the pattern.
The large number of moving parts need a small amount of grease from new to prevent wear.
The use of grease in a lock system is unusual as graphite powder is the standard lock lubricant for most locks.
The small springs in the lock that adjust component position are easily overcome by an accumilation of grease, muck and condensation.
This can cause a lock to spin or refuse to turn even with a good key.
They can be particularly troublesome this weather when the condensation freezes.
The standard lock treatment of squirting graphite powder into the lock will just make matters worse.
I would try a bit of compressed air first on the locks to see if that shifts the critical gunge in the lock.
Failing that a few squirts of penatrant such as PlusGas may free off the gunge.
If not Noz has put an excellent door lock servicing guide in the self help.

The Mk2 XM RF Plip sets are fixed coded from factory.
Each Plip has its own unique pair of rolling codes.
These codes are in addition to the Plip sets unique identification code.
Unique identification includes a subset to tell the plips apart.
This is needed so that the receiver uses the correct pair of rolling code for that plip.
Each key press transmits a scrambled combination of identification and one of the two rolling codes.
The receiver has an unscrambler to seperate out identification and rolling code from the signal.
It then checks out the identification first then if correct the current rolling code for that plip.
Only after both data sets are found correct does the car unlock.
Both Plip and receiver then roll on to the next rolling code in the sequence for that plip.
This means that every time the same plip is used a different scrambled code sequence is transmitted.
That security feature was to prevent a thief with a radio scanner reading and recording then reusing the plip message.
If the plip is used out of range of the receiver the plip will still roll over to the next rolling code but the receiver will not.
This is why a plip may sometimes need to be pressed twice to get the car to unlock.
Peter has covered the Plip set checkover pretty well.

From the above you will see that you have two seperate problems each occasionally giving the same locked out the car result.
Only when they combine are you really stuck.
Clear one alone and you can get by.

On locks I tend to go for new sets with factory keys if the problems are frequent.
New door pairs with 2 keys can be obtained for about £25.
On plips your post has prompted me to realise that a receiver failure can make a set of two plips useless and is not unknown.
By default I have overcome this risk on a couple of my XM's.
I have a collected a few receiver and single working plip part sets.
I ran out of full sets so to get two working plips in those cars I wired in a second receiver in parallel with the first one.
That works fine, I realised it was possible when the ex Diplomatic XM was sold on ebay with more that 2 working plips.

John

John,

Many thanks for taking the time to give such a learned, helpful and detailed reply. This is worthy of a "sticky", or a help page file.

I did wonder if the issue was somehow weather-related, as we've had an odd mixture of freezing sleet and sharp frosts here, moisture that penetrates over a long period, then freezes.

Rob

Hi Rob

It was just going to be a few lines in answer to your questions.
So I started and decided to collect all the related info in one place.
Trying to do this on a few answers now and add source details as well.
Thought it might help to bring a bit more activity to the site.

John

For the key rotating in the locks, have a look at this.

http://club-xm.com/forum/index.php?showtopic=250

HTH

Many thanks!

A Knighthood for Noz?

r

For the 2.5TD I'm considering adding an aftermarket remote locking unit. Has anyone done a writeup on adding this? The Texton box is present on my car, but I have no working plips - not sure the plips that came with it are even for it.

Hi BeckyR

The Texton box has the remote set unique code number marked on it.
First item below the lower bar code.
One I have to hand is marked "Code elec: E3C113".
The plips each have their own marking.
Remove the small screw in the channel the key blade folds into then pull the plastic case apart.
On the case just above the batteries should be a little white sticker.
The plip I have just taken apart is marked "3C113.0".
The other plip in the set will be marked "3C113.1".
The .0 and .1 inform Citroen which set of rolling codes that plip uses.
Those rolling codes are not available even to dealers, just used when manufacturing a replacement plip.

Each set has its own code elec and you cannot make up working sets from mixed code items.
From this description you should be able to check that all your plip components are from the same set if they have a common Code elec number.
Servicing and repairing matched sets often works.

The Mk2 XM plip set is an early version of the RF system.
As a result it is non standard in the signals from its button functions.
Its wiring is also at variance from the modern standards.
The aftermarket plip sets are not a perfect match for the XM despite the claims of the sellers.
These aftermarket sets can be made to work in an XM but not easily.
There have been a few posts one here by people describing fitting aftermarket sets.

John

Just to close this one off, a few sprays of dry lube (the stuff used on bike chains that's not meant to attract grit), plus some work with the key got the lock working for now.

Thanks, all!