xantia ecu fault

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timmsd
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xantia ecu fault

Post by timmsd »

I've got a xantia 16v 1.8 with an intermittant fault.
It turns over fine but won't fire.
If I knock the ECU a few times it works. Then it seems OK until left a while and then no start. Interesting?
Is there anyway I can check where the fault is?
Is a code stored somewhere that can be read that is not lost when it starts to work again?
I've been told that the fault lay in the wiring connector in the inner wing but this looks OK to me.
If I get a s/h ecu do I need the code as well?
Dave
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Post by arry_b »

sounds like a mechanical problem with the connections to the ECU rather than a dead ECU - transistors and ICs dont fix themselves when you bash them!
Clean all the connectors and the earths to the ECU see how you get on.
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JamesQB
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Post by JamesQB »

I've got a Xantia 1.8 16V and I recently (few months ago) cleaned up the connector that plugs into the ECU. It's an easy job, just remove the big connector, visually inspect both the connector and socket for any residues, dirt, etc and clean with a toothbrush and some alcohol. Then spray liberally with WD40 and insert and remove the connector into the ECU a few times.
If this doesn't sort it out and you have experience with soldering, then you can remove the ECU completely - get it on a clean bench, connect yourself to an earthing strap (beware of using a metal wire connecting you to an earthing point if you're near anything that is supplying mains voltage, as proper earthing straps have an integral high-ohm resistor in series with the lead to ensure that if you do take any voltage, it doesn't zap through you at high current) and undo the screws holding both parts of the ECU casing together. Carefully remove the board inside and visually inspect for dry joints. The ECU I opened had lots of dry joints and I did them all, ECU is still working perfectly.
Re-solder all dry joints, visually inspect your work to ensure you haven't inadvertently soldered two areas together that shouldn't be connected and no solder blobs have dropped on to anything, creating a short and then clean the areas soldered with toothbrush + alcohol to remove flux residue making it a professional job. Dry thoroughly and put back together after yet another visual inspection to ensure no areas have been soldered together that shouldn't be, especially from excess solder flow. Stick back in car and keep fingers crossed that a) it works and b) it stays working this time.
I once read on a company for ECU repair's website that a large proportion of ECUs that are simply replaced with a new expensive one when they become faulty are in fact repairable with most faults being due to dry joints. This isn't news to anyone in the electronics industry, as they know that a large percentage of TVs, videos, sat receivers, etc that come in for repair just need solder joints re-done that have become 'dry'. A good amount of the equipment that came in to me for repair just needed dry joints attending to, not that the customers enjoyed finding that out, they thought it such an easy task that it should be done for 5p. Just remind 'em who the person is who knows what dry joints are, who can spot them and have the knowledge to put them right... I'm ranting again... keep Joe Public away from me!
Anyway, all going well it may work after cleaning the socket and connector with some WD40 or Switch Cleaner, I reckon it will. If not and you don't know much about dry joints and soldering, send it to me if you're in the UK and I'll happily do it for nothing more than postage costs, although no guarantee it will do the trick if the fault lies elsewhere...
I'm off for another cuppa. [|)]
timmsd
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Post by timmsd »

Thanks for your comments. I had assumed it may be a dry joint in the ECU and that is something I can address. I've checked the plug and it looked OK but I will try cleaning it thoroughly before looking more closely at the board.
If I visually inspection the board with a magnifying glass, how can I tell which joints are bad conductivity? Usually I just resolder them all.
ps thanks for your kind offer to look at it for me, very gereous. Thanks
Dave
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JamesQB
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Post by JamesQB »

I've tried to find pictures of dry joints but can't find any and I've nothing to hand to use my digicam on to show you so I'll try to paint a picture with words... A good solder joint should be smooth and shiny with no telltale 'rings' visible in the solder centered around the component leg. A dry joint can look dull, crinkly and/or have a slight ring visible centered around the component, this ring usually appears as a very thin darker line and in extreme cases a visible crack. I've seen dry joints so bad that you have the solder around the component leg, a visible gap and then the remaining solder that sits on the pad on the PCB!
By the sounds of your fault, if it is a dry joint, then I'd expect it to be a visible one as it must be fairly severe if banging the ECU makes the car work again, this shows physical movement is possible between the two lots of solder that should be connected.
Good luck,
James
timmsd
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Post by timmsd »

James
Many thanks
I'll let you know the verdict.
Dave
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Post by AndersDK »

Usually it is electronic components dissapating heat that will break up and make for dry solder joints.
Or large components which can vibrate - like electrolytic capacitors & relays.
Easy to recognise - as these also will have the largest solder pads.
It will never (at least very rare) be the multileaded IC's or the tiny 2-lead resistors etc.
Note that all automobile ECU's will have a corrosion protective layer all over (at least those I've seen) - which must be touched up after any repair.
I'd be absolutely sure it's not any external cable/connectors/contacts that's the problem - as fiddling with the electronics board itself compares to heart surgery [:I]
Donno on the xantia ECU - but CX series2 ECU's have an external (box) ground that's prone to fail - which makes for mysterious starting problems.
Another common problem is too low battery voltage reaching the ECU. It's wellknown that the ECU's may start hickup at voltages less than approx 11V.
Could be worth checking your battery in fact !
timmsd
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Post by timmsd »

Looked long and hard at the ECU board. Nothing out of the ordinary. Cleaned up socket contacts. Still won't fire.
I then turned my attention to the brown, sealed unit in the box with the ecu. Shake this about and she fires. Then starts fine time after time. Leave for 4-5 hours need to shake the brown box again.
So I think I have isolated the problem but what is the brown box? I think its to do with the coded immobiliser but I thought this was contained an IC within the ECU. Disconect the brown box and I get the red + green lights on the code panel indicating a fault. The box has BITRON on it. The car does not have air con.
Any ideas?
Dave
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AndersDK
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Post by AndersDK »

Any chance this brown unit is the external power relay for injectors/fuel pump ?
These relays of later generation is commonly a twin relay with some electronics logic build on - known to fail.
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Post by ZXturbo_Aura »

if need be, im sure i spotted a ECU for a xantia 1.8 for sale on ebay, was only about 5 quid!!
Dan
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Post by RichardW »

http://www.bitron.it/products/auto/G3/auto3.html#42
Seems Bitron make all sorts of things (not just the infernal A/C controller!) including this dual relay jobby, which looks suspiciously like what Dave is describing, and would fit Anders' thoughts about fuel pump relays etc. Time for a trip to the scrappy I think....
timmsd
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Post by timmsd »

Richard
Thanks for the link. Yes that is the brown relay box.
I spoke with citroen who confirmed this is the injector relay. I expect this forms part of the immobiliser and so when the relay is disconnected the keypad shows the red/green lights simultaneously to indicate a fault.
Can I disconnect the key pad and immobiliser in some way. I would prefer to like with out it.
Dave
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Post by wheeler »

put the code into the keypad to unlock it then disconect the plug from the back of it,you should'nt need to enter the code again.of course if the injection ECU loses a feed then it will still fail to start.the ECU gets some of its feeds from the double injection relay.
timmsd
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Post by timmsd »

Hi Russell
Long time no here. Trust the Activa is OK?
Dave
ps thanks for the info. I find the key codes really annoying
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