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Old 15-12-2019   #1
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Immobiliser problem

Hi all looking for a little advice. I have a 2004 2.8 Ducato Motorhome, when I turn the ignition on the immobiliser light stays on and it fails to start, now if I go to the fuse box under the bonnet and pull out the put back in a 7.5 amp fuse the turn the ignition on again the light goes out and it starts normal it also starts after a run but the same problem happens again the next morning, itís almost like a relay is being held or something, any ideas please.
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Old 16-12-2019   #2
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Re: Immobiliser problem

Hi, good luck been trying to cure mine for over 12 months, mines intermittent, 2005 hymer,
The control box is under steering column, take the lower cover off, white plastic box size of a flag packet with the ignition sensor there as well, our Fiat garage said to change both £300 for parts, but in our case they could not code the keys to the new box, suspect wiring fault can't afford £100 per hour for them to play. When we have the fault we unplug the box it seems to reset it? We had a mobile guy come and look said there were 194 keys assigned to the van? Ours is ok for weeks at a time then may fail 12 times in succession, can't get anyone interested because it's intermittent they won't commit the time to it, if you find an answer let me know!
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Old 17-12-2019   #3
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Re: Immobiliser problem

Quote Originally Posted by Fuseman View Post
Hi all looking for a little advice. I have a 2004 2.8 Ducato Motorhome, when I turn the ignition on the immobiliser light stays on and it fails to start, now if I go to the fuse box under the bonnet and pull out the put back in a 7.5 amp fuse the turn the ignition on again the light goes out and it starts normal it also starts after a run but the same problem happens again the next morning, itís almost like a relay is being held or something, any ideas please.
I assume that the 7,5A fuse that you are removing and replacing is F18, which normally provides a permanent (24/7) supply to the Code Control Unit.


Unfortunately there are no relays that could latch closed, so the most likely causes of failure are thermal with a micro crack in one of the components, or a firmware problem causing a lockup in the software.

I am sure that any simpler explanation would be most welcome.

The external wiring of the CCU, is relatively simple. It consists of a dedicated positive supply from fuse F18, with an earth connection at or close to the ECU. There is a short 2 core screened cable to the aerial on the ignition switch. Outputs are to the code lamp, and to the ECU. Finally there is a connection to the diagnostic socket.

The output or communication to the ECU is routed via connector D004 pin C19, and the earth connection is via D004 pin A2.


I believe that connector D004 is the multiway connector, under the engine bay fuseboard. I have read of corrosion occuring in this area, and the possibility could be worth eliminating.

To access D004, first disconnect the battery negative post. The fuseboard can then be unlatched, and carefully moved aside.
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Old 20-12-2019   #4
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Re: Immobiliser problem

Thanks for the info guys, fortunately the Motorhome is still under warranty so itís going back to the dealers after new year, Iíll post up what they find
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Old 03-01-2020   #5
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Re: Immobiliser problem

Thanks communicator a bit more info taken in, today I checked the multipin plug under the fuse box, looked fine but used contact cleaner on it anyway,

I can't see an earth connection at the Ecu with the cover removed just multipin plugs on bottom edge

However there is a very heavy metal bare ended cable bolted to the side of the fusebox on air filter side it disappears into the loom is this an earth point?

My control box under steering column multi plug has 6 cables, black, green, yellow with blue tracer, blue with orange tracer, red with yellow tracer, blue any idea which of these go where?

The other plug is the aerial to the ignition switch which is new

Appreciate any help thanks
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Old 03-01-2020   #6
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Re: Immobiliser problem

@Brian snail
Where are you located? I can't reist a challenge

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Old 03-01-2020   #7
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Re: Immobiliser problem

Thanks I'm in Gloucester it might be ok for weeks then fail? Times I've thought it was fixed then out of the blue it fails?
The confusion arises from my dealer fitting a new control box but unable to code my keys to the new box, they said they could read ecu but not key coding? Which is why we keep looking for wiring faults?
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Old 03-01-2020   #8
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Re: Immobiliser problem

Is the Dealer Fiat or Motorhome? Not many diagnostic systems can program the keys.


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Old 03-01-2020   #9
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Re: Immobiliser problem

Fiat professional main dealer, Imperial commercials.
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Old 06-01-2020   #10
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Re: Immobiliser problem

Oh dear my last comments seems to have scared you off?
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Old 06-01-2020   #11
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Re: Immobiliser problem

Quote Originally Posted by Brian snail View Post
Oh dear my last comments seems to have scared you off?
No, just thinking about it. Not sure why a supposed expert main dealer can't sort it out.
Did they quote you for fitting the new ECU? If they did it's easier but bsically if they fitted it they should sort it out. The only other thing that it could be is the transponder antenna or it's connections. This is just a coil of wire round the key hole. However that does not tie in with the original fault.
What ECU is fitted now, the old one?
I'm a bit far away, Cambridge, to come have a look.


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Old 06-01-2020   #12
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Re: Immobiliser problem

You can program the keys in the eeprom in code unit using zed bull, tango and others auto locksmith can do it. It's a rolling code transponder so the code unit changes the code, if you have low voltage e.g. bad earth, bad battery during this negotiation you can end up with scrambled data. The fact you were told there were 194 keys suggests to me this is the case.
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Old 06-01-2020   #13
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Re: Immobiliser problem

Hi Robert, the Fiat dealer ordered and fitted replacement control box and aerial but could not program my keys to the new box? Refitted the old one, they had it for three weeks just kept saying it was my sigma alarm blocking there coding, my sigma alarm is not possible to cause this direct answer from sigma, they flatly refused to believe sigma and told me to remove my vehicle from their premises this is who have serviced my vehicle for the last 7 years, they still charged me £600 needless to say we fallen out with them now! Ecu has not been touched, I have spoken to many "experts" but because it is so random they don't want to know?
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Old 06-01-2020   #14
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Re: Immobiliser problem

Hi corcai, I don't understand anything you said there I'm afraid, just a nut and bolt man, spoken to locksmiths they just don't want to help?
We have had the van from new so know everything that's been done to it.
I have found squashed cable under the handle for steering wheel adjustment, replaced 18 inches of cable and multi plug from a doner van soldered and heat shrunk the connections didn't fault for three weeks after! Tried the connections you said, new aerial is still on, van has never had a flat battery or jump started, unplugging the control box seems to reset it, can you help with my earlier post regarding the wire colours and where they go?
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Old 06-01-2020   #15
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Re: Immobiliser problem

Robert appreciate your offer of help 125 miles apart? Is this your trade? Do you have a garage?

I have a local friendly mobile guy who at the moment has a copy of my ecu program on his laptop and the new control box to see if the new box could be cloned from original so keys would not need coding, don't know if this is possible?

I am a bit scared of sending ecu and boxes to be 're programmed by adverts on eBay etc.
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