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IronKettle



Member Since: 08 Dec 2024
Location: Lincolnshire
Posts: 10
United Kingdom 2000 Defender 110 Td5 CSW Alveston Red
TD5 Immobiliser tripping?
Hello everyone!

I've got a 2000 TD5 110, everything was running and starting fine until one morning it just refused to turn over.

I've got my scope out and started probing and found that the relay inside the cab isn't clicking at all. Jumping this relay to trigger the starter motor gets the truck running for about a second before it cuts off again.

Following this wiring diagram, I can see I'm getting 12v when turning the key as expected (ignition switch is fine).
But around 9v at the other side, where I would have expected to see ground (see attached image).


Click image to enlarge


Have I somehow tripped my immobiliser? If so how on earth do I reset it?
Truck has no central locking and no key fob so changing the battery won't work!


Any tips or suggestions would be much appreciated.
Post #1071464 15th Jul 2025 10:43am
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Penfold_6290



Member Since: 22 Sep 2021
Location: Dorset
Posts: 385
United Kingdom 2002 Defender 110 Td5 CSW Epsom Green
The immobiliser ECU provides an earth path for the starter relay which explains why you have 9v on the 'earth side' of the relay coil, see screenshot below). Only when the immobiliser is deactivated will the immobiliser ECU allow you see an earth here.

The fuel pump is also affected by the immobiliser, which explains your run for one second and then dies routine. The engine ECU is informed by the immobiliser ECU, the engine ECU then provides an earth for the fuel pump relay.

I'd say get friendly with someone with a Nanocom so you can see what the alarm/immobiliser is doing.

Last edited by Penfold_6290 on 15th Jul 2025 11:37am. Edited 1 time in total
Post #1071470 15th Jul 2025 11:33am
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Penfold_6290



Member Since: 22 Sep 2021
Location: Dorset
Posts: 385
United Kingdom 2002 Defender 110 Td5 CSW Epsom Green

Click image to enlarge



Click image to enlarge
Post #1071471 15th Jul 2025 11:35am
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Penfold_6290



Member Since: 22 Sep 2021
Location: Dorset
Posts: 385
United Kingdom 2002 Defender 110 Td5 CSW Epsom Green

Click image to enlarge
Post #1071472 15th Jul 2025 11:36am
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IronKettle



Member Since: 08 Dec 2024
Location: Lincolnshire
Posts: 10
United Kingdom 2000 Defender 110 Td5 CSW Alveston Red
Unfortunately I don't know anyone local that has a defender nanocom to check the codes out.
ECU has been sent off to have the immobiliser removed for good!

Once that's done I'll manually ground the relay coil so its not reliant on the alarm and all will hopefully be back to normal!

I've never had a keyfob so I suspect the alarm had been soft disabled at some point in its life and it somehow reset.
Post #1071521 15th Jul 2025 8:00pm
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