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Immobiliser Problems


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I'm posting this in the hope it might help someone else in the future.

The scenario was as follows:

"P" reg (300 shape) 5 door disco with 3.9 V8, manual box and sequential LPG injection.


Died one day, occassionally starting but not for long, problem diagnosed as no sparks to the plugs but power getting to the coil.

The coil and module were replaced to no avail. power straight from the battery to the +ve on the coil and engine fired up.

After a lot of searching on Rave, the immobiliser controls 3 ccts.

power from fuel pump relay to fuel pump

power from the ignition switch, in the start position, to the starter


power from the ignition to the coil

The immob. module is screwed on top of the heater, below the radio in the centre of the dash and is a right pig to get to.

A replacement one is £140 retail ish and I'm a Scotsman so the old one was dismantled and inspected.

These things are connected with 9 wires and they're all Black so be carefull!

The problem was traced to a dry solder joint on the printed cct board on the coil side of the relay.

This is why it sometime would and then again maybe not..

Cleaned, resoldered, reassembled, swore (several times) and tested even more times and things are looking good.

I'll post a photo of the stripped module but as I was working outside the house last night in -1oC I've no shots of the dash stripdown.

I'll try to answer any questions.

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