2000 Xantia S2 2.0L Petrol - Body Computer

[ozrkr]

Does anyone know whether the Body Computer (aka Central Protection Unit) has any control over the operation of the fuel pump?
eg. 1: is there an interlock on the fuel pump instigated by the Body Computer? If so, what causes the interlock to be applied / released?
2: Does the Body Computer cause the fuel pump to prime the fuel system in any situation? If so, what situation initiates the priming?

Does anyone have a detailed wiring diagram/functional diagram that describes the operation of the Body Computer? I do have the Haynes workshop manual wiring diagram but it is at a very high level - it shows the Body Compter only as a black box ...

Has anyone removed the Body Computer? If so, are there any explicit 'how to' instructions readily available?

If anyone has removed the Body Computer, has anyone attempted to repair it in any way? What is likely to be wrong with it? Is it repairable?

I am attempting to resolve a very weird problem with my car. Any help that anyone can give me on this would be greatly appreciated!

[wheeler]

The CPH has nothing to do with the fuel pump.
The fuel pump is controlled entirely by the injection ECU via the 'Double' relay.
The CPH controls Alarm, immobiliser, Central locking & interior lighting.
It has a connection to the injection ECU as it sends the command from the immobiliser to unlock the ECU. Although the CPH has the immobiliser function built in to it im pretty sure the immo does not inhibit the fuel pump.
The CPH is located up behind the glovebox on RHD models, if i remember right if there is a passenger airbag this needs to be removed to get to it.

What is the issue you are having with the car?

[ozrkr]

Many thanks, wheeler, for your reply.

My problem is truly weird, but can be summarised as:

When the ambient temperature is low - say after the car has sat outside overnight during autumn or winter, several symptoms are apparent:
1. The 'door open' indicator lamp either does not light up at all, or flashes. The indicator is controlled by the Body Computer.
2. The interior lamps either do not light up at all, or they flash - in sync with the 'door open' indicator. The lamps are controlled by the Body Computer.
3. I hear what sounds like a relay clicking, in sync with the 'door open' indicator and the interior lamps - the clicking appears to come from the Body Computer, and the big one ...
4. The car does not start. The battery is strong and the engine turns over well, but without firing.
The not starting appears to me as if there is no fuel being fed to the injectors, as if there is some sort of interlocking in force, perhaps linked to the strange behaviour of the Body Computer?

And by way of my very cludgy work-around:
If I run a 240V fan heater for 15 minutes prior to trying to start the car, aimed at the Body Computer, everything operates as per normal:
1. The 'door open' indicator lights as per normal
2. The interior lamps operate as per normal
3. There is no 'relay clicking' noise coming from the Body Computer
4. The car starts as per normal

Your comment 'It has a connection to the injection ECU as it sends the command from the immobiliser to unlock the ECU' could well be very relevant. If, for some reason the CPH did not send the command to unlock the Injection ECU, it could explain my problem ...

[wheeler]

OK do you know your RP number so i can get a wiring diagram?

I think i would definitely be removing the CPH to check for dry solder joints, the connections or water ingress.
Is the immobiliser/key light flashing when it doesn't start?
Do you have Lexia?
So its not just a case of the fuel pump not Running? If the CPH wasnt unlocking the ECU then i believe the fuel pump will still prime but the injectors just wont operate.

Next thing worth a check, in my 25+ years of doing car repairs day in day out one of the most obscure faults i ever saw was on a mk2 Xantia, i have seen the fault twice now personally & know of someone else that has had it. The first time i came across this it taken me around 3 days to find the fault, the symptoms were slightly different just a non start with the immobiliser light flashing, however given your symptoms it may be relevant. This Xantia was a non starter with immo light flashing, after several days of wiring checks & pretty much swapping the whole immobiliser system (CPH, ECU & keys etc) from a donor car and a lot of head scratching long story short it was a faulty drivers door latch mechanism that was causing (yes that wasn't a typing error, the door latch was causing the car not to start). As soon as i unplugged the drivers door latch the car started no problem, plug it back in, no start again. After starting afresh i noticed the drivers door latch has a direct connection to the CPH. i can only assume that somehow it was internally shorting or backfeeding the CPH. Anyway replacing the door latch sorted it & a couple of years later i got another one in with the exact same fault only this time the first thing i done was disconnect the door latch, it was the exact same thing. Someone else i know phoned me for some advice one day after having a similar fault. i told him to unplug the door latch & he thought i was winding him up or loosing my marbles, an hour later he called me back gob smacked.

I know your symptoms are slightly different but could well be relevant, i would be pulling the door panel off then wait to the next time it wont start & then disconnect the door latch & see if it will start.

If it turns out the CPH is faulty you may well know that these are coded to the car & you cant just plug a used one in.
The options would be get a new one & program with Lexia, 4 digit security code would be needed for this. Also you may find that part is no longer available but servicebox is currently down again so cant check.
Option 2. Get a used CPH & swap the EEPROM chip from your one to the 'new' one. Or re write the data onto the new one (This would depend on your skill set & equipment)
Option 3 get a used matched set of ECU, CPH & key from another car.

[xantia_v6]

Another somewhat weird fault that is temperature dependant is an intermittent solder joint in the dashboard fusebox, causing one of the ECU supplies to be absent (sometimes failing when hot, sometimes when cold). Yours being a late car, may have a different fusebox.

[Stickyfinger]

As the fault goes away when the interior is "heated" I would lay my bets on a dry joint somewhere......

[XantiaNonStarter]

Is the post by Xantiamanolis towards the end of this thread relevant?
viewtopic.php?t=71100

Faulty capacitors that need to be replaced

[ozrkr]

Is the post by Xantiamanolis towards the end of this thread relevant?
viewtopic.php?t=71100

Faulty capacitors that need to be replaced

I wanted to give an update to my cold weather start6ing problem. It is now fixed, as described by xantiamanolis in the above referenced topic.
Many, many thanks to xantiamanolis for the guidance on the Body Computer fix! And to CitroJim for his guidance on locating and removing the Body Computer.
Very much with their help I have been able to fix a problem that I have been chasing for two years! Many thanks!