Xantia Immobilser Problem

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XantiaNonStarter
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Joined: 01 Feb 2022, 17:21

Xantia Immobilser Problem

Post by XantiaNonStarter »

I own a Citroen Xantia (2001 1.8i 16v petrol.) Back in January the immobiliser came on. If I turn the key, the car starts beeping and the dashboard immobiliser light comes on. The starter motor runs but the car won't start. If I bring the key near the Texton, the car also starts beeping (but only if the door is open.) If I lock the car with the key fob, the central locking works but the car then immediately unlocks itself. I can force the car to lock by using the key manually.

I have tried the spare key. I also bought a new car battery. I have also cut off the positive battery terminal and replaced it to rule out corrosion.

I am so grateful to Xantia owners who have had similar immobiliser issues and posted on this forum. What I have gathered from these posts is that it's a common problem and often caused by voltage problems at the ECU pins which in turn track back to the wiring loom that runs across the car near the bottom of the radiator.

Here are a couple of examples:
viewtopic.php?t=55006
https://www.frenchcarforum.co.uk/forum/ ... =3&t=54176

I have no previous experience of car electronics but am trying my best to learn. I can't find an injection wiring diagram for my RHD car but have found a LHD one. The ECU is an 88 pin Bosch MP 7.3 05.

There is a double relay next to the ECU and I checked input pin voltages with the relay out. Pins 2, 8, 11, 14 and 15 had 12/13v as expected.

I then checked voltages on the most relevant pins with the relay and ECU plugged in. The results are below:

Relay
pin 05 0v
pin 07 12.03v
pin 10 12.03v

Relay with ignition key turned
pin 05 12.2v
pin 07 1v
pin 10 11.6v

ECU
pin 15 12.04v
pin 21 0v
pin 33 0v
pin 49 12.47v
pin 50 12.02v

ECU with ignition key turned
pin 15 11.62v
pin 21 11.88v
pin 33 12.32v
pin 49 12.3v
pin 50 0.95v

The ECU earth pins seem ok. Pins 1, 6, 23 and 28 are all 0v and have <1 Ohm resistance to ground.

Please can anyone help interpret the above results or spot the problem?
Many thanks.
RichardW
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Re: Xantia Immobilser Problem

Post by RichardW »

Difficult to tell without the diagram, but pins 7 and 50 that go down to 1V with the key on look suspect...
XantiaNonStarter
Posts: 5
Joined: 01 Feb 2022, 17:21

Re: Xantia Immobilser Problem

Post by XantiaNonStarter »

Sorry I have the diagram in svg format but the attachment failed
Have converted to jpg format (with some loss of quality)
Hope the attachment works this time!
Attachments
1.8i16vInjectionCircuit.jpg
wheeler
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Joined: 21 Sep 2002, 19:07
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Re: Xantia Immobilser Problem

Post by wheeler »

Can you check are you getting 5v at any of the MAF sensor pins with the ignition on?
Do you have Lexia and your immobiliser security code?
Its not unknown for CPH equipped cars to just loose the key coding & need reprogrammed.
XantiaNonStarter
Posts: 5
Joined: 01 Feb 2022, 17:21

Re: Xantia Immobilser Problem

Post by XantiaNonStarter »

Thanks RichardW. I just checked the input side of the relay.

Relay
pin 08 12.43v
pin 14 12.43v
pin 15 12.43v

Relay with ignition key turned
pin 08 12.24v
pin 14 12.43v
pin 15 12.2v

I don't know if the voltage drop at output pin07 on ignition is expected behaviour?

Wheeler, thanks for your help. I have the immobilser code card and back in January a mechanic kindly came to visit the car on my drive. He had a Lexia (or equivalent) and hoped to reprogram the car to see the keys. However, he couldn't see the ECU/CPH with the Lexia. I had to google what a "MAF Sensor" is :-) It will take me a few days to have a look at that.
wheeler
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Joined: 21 Sep 2002, 19:07
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Re: Xantia Immobilser Problem

Post by wheeler »

Sorry, i just noticed this was a petrol so you wont have a MAF sensor, however it will have a MAP sensor & you can do the same check for 5v there.
Did you check any of my tips from the previous posts about checking the inertia switch hasn't tripped & removing & cleaning the gearbox earths (even if the appear to look OK).
Another piece of advice is doing a resistance check on an earth circuit is not a good indicator of how good an earth circuit is even if its showing half an ohm, you really need to check them with a load like a proper filament bulb (not LED). There could be a single strand of copper left on the wire & it will show 0 ohms resistance but may not be able to carry any sort of load.
XantiaNonStarter
Posts: 5
Joined: 01 Feb 2022, 17:21

Re: Xantia Immobilser Problem

Post by XantiaNonStarter »

Thanks for your help Wheeler; I am working through your suggestions gradually.

The inertia switch is ok. The ball bearing has not popped up. The voltage at pin 15 of the ECU shows it's ok I hope.

I had a spare indicator bulb and used that to do a voltage drop test on the 4 ECU earths. The voltage drop was only 0.05v for each pin.

I tried a fused wire from the positive terminal of the battery to pins 8 and 15 of the relay but it didn't make a difference.

A day before these problems started, I topped up the coolant. I just found the gearbox earth and there is coolant collected in the ridges of the gearbox beneath it. I disconnected the earth and gave it a good clean with contact cleaner. Unfortunately that hasn't fixed the immobiliser problem.
XantiaNonStarter
Posts: 5
Joined: 01 Feb 2022, 17:21

Re: Xantia Immobilser Problem

Post by XantiaNonStarter »

Good news! Yesterday I fixed my car (or perhaps it would be fairer to say it fixed itself.)

Until yesterday, the car could be locked with the key fob, the central locking operated but then immediately unlocked again. Things got worse yesterday when the passenger door entered an in-between state where it was unlocked but would not open.

Eventually I got the door open and suddenly all other problems disappeared: the car could be locked with the fob, the immobiliser problem disappeared and the car could be started.

There was something wrong with the passenger door lock which in turn caused the immobiliser issue. I will take the door apart but the problem is not there anymore so I guess will be difficult to find.
Hell Razor5543
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Re: Xantia Immobilser Problem

Post by Hell Razor5543 »

I wonder if the wiring in the concertina grommet (between the body and door) has become damaged. It is known that the wiring fails there. I had this on my second Xantia (one rear door was deadlocked and non-responsive, the other rear door wouln't lock), and I found failed wiring for both doors. Once I sorted them out (added 6" wire at each failure) both doors behaved properly.