Fault Code A799 No communication with Immobiliser

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Langym93
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Joined: 27 Jan 2025, 21:56

Fault Code A799 No communication with Immobiliser

Unread post by Langym93 »

Hi,

So I have an issue with my C1. The car would start and cut out so i’ve plugged my dyno in and got the error code A799. So I contacted Citroen and they said it sounds like I need a new Immobiliser. Before I went a head and got a new immo my friend who is an auto electrician plugged his dyno in which is an expensive bit of kit. Anyway he said he can’t communicate with the immobiliser. And most likely need a new one. So I’ve got my new immo which is virgin. We’ve put the new immo in and still his dyno can’t communicate with the immobiliser. But I have asked him if the new immo needs to be coded/synced to the car as it’s a virgin immo and thats why he can’t communicate with it? Watch some youtube video were someone syncs a virgin box himself using number 4 and 13 pins on the OBD.

Just so confused at the moment now, my friends starting to think it’s a wiring problem now? Any advice would be much appreciated because I don’t want to get someone else out to check over wires when it could simply be because I need to sync the new virgin box to the car
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xantia_v6
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Re: Fault Code A799 No communication with Immobiliser

Unread post by xantia_v6 »

Which engine does your car have?
Langym93
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Joined: 27 Jan 2025, 21:56

Re: Fault Code A799 No communication with Immobiliser

Unread post by Langym93 »

Just a 1 litre
Langym93
Posts: 4
Joined: 27 Jan 2025, 21:56

Re: Fault Code A799 No communication with Immobiliser

Unread post by Langym93 »

xantia_v6 wrote: 27 Jan 2025, 22:36 Which engine does your car have?
1 litre
wheeler
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Re: Fault Code A799 No communication with Immobiliser

Unread post by wheeler »

What year is it? Mk 1 or 2? Now looking on a laptop i can see profile info & as its a 2014 will be a mk1

Yes you sync immo box by shorting pins 4 & 13 of OBD socket, however you should still be able to get comms with it even before it is synced. You can actually go in & program the keys first on a virgin immo box then do the sync after. You need a wiring diagram & go from there.
Last edited by wheeler on 28 Jan 2025, 18:38, edited 1 time in total.
Langym93
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Joined: 27 Jan 2025, 21:56

Re: Fault Code A799 No communication with Immobiliser

Unread post by Langym93 »

wheeler wrote: 28 Jan 2025, 14:55 What year is it? Mk 1 or 2?

Yes you sync immo box by shorting pins 4 & 13 of OBD socket, however you should still be able to get comms with it even before it is synced. You can actually go in & program the keys first on a virgin immo box then do the sync after. You need a wiring diagram & go from there.
I’m not getting any communication to my Immo at all as well as power steering ECU and ABS
wheeler
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Re: Fault Code A799 No communication with Immobiliser

Unread post by wheeler »

Have you checked all the fuses & fusible links?
Any more background info on the fault? had any work been done on the car just prior to the fault?
Using the diagram below check the power supplies & earth to the immo unit. Now with the new information you have added on about comms issues with other units you may find there is a shared fuse blown.
The immobiliser is a very basic system on this car & normally trouble free, never heard of an immobiliser control box failing on one.
Attachments
C1 immo.jpg