Defender TD5 won't stay locked, alarm and immobiliser problems too

My truck isn't staying locked, I'm only using the key not the fob because when I use the fob the alarm goes off and then everything unlocks. Also on a few occasions the immobiliser has come on, feels like I may have more than one problem here but not sure where to start. I've spoken to one guy at Alive Tuning who said that they can disconnect the immobiliser for £200 + vat, but that won't help the locking problem....please any suggestions??

This usually happens if one of the doors is not closed properly or the bonnet, if all are closed the most common cause is the alarm trigger switch under the bonnet on the bulkhead near the servo, try bending up the bracket slightly and straightening the switch which has a rubber cover, it may be leaning to one side and not making full contact with the bonnet when closed. Also check the light switches in the door posts are operating.

My alarm issues were the ultra sonic sensor on the inside, to test it I just pulled it out head lining there is a connector on the back I just unplugged it and no trouble after that, cost me £60 for a new one didn’t have any trouble after that.

Scooby22 said:

This usually happens if one of the doors is not closed properly or the bonnet, if all are closed the most common cause is the alarm trigger switch under the bonnet on the bulkhead near the servo, try bending up the bracket slightly and straightening the switch which has a rubber cover, it may be leaning to one side and not making full contact with the bonnet when closed. Also check the light switches in the door posts are operating.

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Thank you I will have a look hopefully it's going to be that! Would that affect the immobiliser?

Tattybird said:

Thank you I will have a look hopefully it's going to be that! Would that affect the immobiliser?

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Dont forget to check the rear door light switch as well, there is a bracket on the rear door that makes contact with the switch, this bracket may need adjustment.
If none of that works check your movement sensors as stated above, by Mcclegend, mine is on the B post behind drivers seat. If that is faulty that would cause immobiliser to operate.