Land Rover Repair: 01 Discovery Door Locks, zero volts, door locks

Question
Hi John,
I am on my second Discovery and I have recently ran into a problem with the door locks that I have not experienced before. A few months ago, I left the Disco running and locked the doors manually with the extra key from the drivers side. Since then, the driver door lock does not respond to the remote or the interior lock switch. Interestingly, it will lock when superlocked with the romote. Manual operation with the key is normal. More recently, I had a import mechanic use an Autologic to check out the problem. There was no explaination when he was finished. The only result that I ended up with was another malfunctioning lock. Now the right rear lock is demonstrating the same problem. Do you know of any procedures to pin point the problem; BCU, micro switch, relay, etc..?

Thanks,
Kevin

Answer
Hi Kevin,

there are so many reasons why the door locks fail that its really sad.  

Its possible in your case that the BCU is misbehaving.

There's a link between the BCU and the IDM "intelligent driver module" that can disable the door locks.  (I'm reaching here...)

Turn ignition on but don't start your Disco for 5 minutes.  This is suppose to reset the link between the BCU and IDM.  The other way is with the dealer testbook.

Other than that, you could try having the BCU reconfigured - again, done by the dealer tesbook.

After that, you could try examining he door latch switch - they send a signal to the BCU.  Perhaps the switch is faulty.  

Here's what LR says:

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The BCU uses the door latch switches to indicate if a door is open or closed. There is a door latch switch within every door latch assembly, including the tail door latch assembly.

Input/Output
The input from the door latch switches to the BCU is either zero volts or an open circuit. Zero volts indicates the door is open. An open circuit indicates that the door is closed. When the BCU sees an open circuit, it pulls the input high internally.

The driver's door latch switch has a dedicated signal input to the BCU. This allows the BCU to identify the driver's door position.

The BCU use a common signal input for the remaining door latch switches.

TestBook provides the ability to monitor the real time state of the door latch switches. Remember that the driver's door is always in a known state. The remaining doors are combined into a single state. The BCU cannot distinguish the state of the individual doors, other than the driver's door.
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Best of luck with this,

JohnMc