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Starting problem. Immobiliser?


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Hi there

I have a '94 300 Tdi Disco Commercial that has developed a starting problem.

I have recently been experiencing some strange happenings withthe alarm/immobiliser and the central locking has stopped working.

Since then the vehicle will only start with the drivers door shut.

Is this likely to be a dirty contacts issue or any other ideas?



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May be worth checking earths and things.

check out the "Definitive Alarm Spider Post" in the technical archive forum, for possble symptoms of the spider problem, and how to fix it. Don't think having the drivers door closed would have anything to do with it though - that sounds more like an earth fault because the door switches go to the alarm ECU and provide an earth when the door is open so perhaps there is another earth that is faulty and that is why removing the earth through the door switch makes a difference - its the only thing I can think of anyway :unsure:

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Being a '94 I am assuming that it is pre spider.

I have had a chance to swap some bits and pieces from another vehicle including alarm ecu but to no avail. I am now tracking wires where I can to check earths and connections.


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It's the single button factory remote.

Then it's not got the spider then. :D

I haven't got a wiring diagram for the 200 series Disco (which I'm assuming yours is).

If you can locate the starter relay, the alarm module should earth the relay to crank it over.

(which I think is predictably the black wire, but may be wrong).

If you earth the wire permanently, it should start/crank from ignition switch.

However the alarm module may also block the power to the injection pump stop solenoid, which will need an

ignition (12v+) feed as well.

Sorry it's a little vague. :huh:

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my 200 with the single button remote has the alarm box on the offside inner wing - same alarm?

my remote died so i took the alarm out. seems the early ones where dealer fit & all you need to do is find the two wires under the steering column with the obvious joins in. disconnect the alarm wires off them & join the wires back together, hey presto 10mins & no more alarm. i ended up ripping the whole alarm loom out just to make it a bit tidier next time i look for an electrical fault.

dont understand the door thing, either what 'Boggy' said or chaffed wire to the door shorting out as it opens - maybe part of the broken central locking?

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Hi there, thanks for the replies.

It is a 300Tdi but an early one with the single button remote and it does start but only with all the doors closed.

I am trying to get hold of a drivers door central locking solenoid t see if the problem stems from there.

There is continuity and zero resistance in wiring through the door to body cable route so am assuming that there is no chaffing or wear to the cables.


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