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Discussion Starter #1
I've been having problems that are related to the BCU for a while.
The auto-lock doesn't work long after I reset BCU settings, the left-rear window control doesn't work when it's damp outside and when it does, it'll close the window on it's own for no reason.
And when that window's closed, I can hear the relay for it on the BCU clicking as if I'm trying to control it.
Tried disconnecting the window control for both the left-rear door and the drivers door, and that relay still has a mind of it's own.
And it's not only the window.
The alarm will activate for no reason roughly around sun-up-ish and sundown-ish.
I use my All Comms to interface with it.

I bought a used BCU and installed it yesterday; reset everything BCU, and the same things still happen with a different BCU.

As far as various vehicle faults, I get a thermostat heater fault ONLY through my All Comms interface - no failures on the cluster.
I have a headlight ballast that's aftermarket, and it doesn't interface with All Comms as the OEM one does, but the headlight works fine.
I've had that installed for years though with no problems.
I also get a sideview mirror position potentiometer fault, but the mirrors seem to work fine, and again that's been there for years without causing any BCU problems.
The Light Control Module doesn't communicate too well with the All Comms, but after a few tries it'll respond.
I checked and cleaned chassis ground points that supply the BCU, no help.


Do any of you have any ideas of what would or could interfere with the BCU?
 

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2002-2005 Range Rover MkIII / L322
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346 Posts
Got it. Have you tried pulling up the wiring diagrams and using a VOM to see if you have a flaky connection, short or power issue?
 

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Discussion Starter #5
Yeah, as far as I see on any lines, no shorts or low impedance to ground. Non between high side and low side of differential lines. Ground points appear to be good, unless I missed any - but I did look specifically at the ones for the BCM.
I want to check the lines for the thermostat heater, but can't identify what wires they are in the ECU box end or at the thermostat.
I've heard the thermostat heater can cause problems.
And I'm not sure about the light control module. Lights work fine, but problems communicating with it, or any K bus comms.
 

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2002-2005 Range Rover MkIII / L322
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The humidity relationship has me thinking it is connection related. Have you looked at the main fuse junction boxes for water issues? The one behind the glove box and the one under the hood? How about the harness at the doors?

I suppose you could pull the door cards on both doors and check all the wires and connections are clean. Maybe open and clean the switches. Remove them all and clean/spray the contacts/pins.

I had a problem on a Volvo where the female connector on the board had corrosion and the board tested fine and everything upstream was new. I finally figured it out when I looked at old pictures of the male side of the plug and saw the corrosion and figured it out - the female side must have corresponding corrosion. Replaced the entire board with a used one and problem was solved. So looking at both sides of the connectors may help. Visually you should be able to see if you have a problem. I know the L322 likes to hold water in the doors.
 

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Discussion Starter #7
I've cleaned the connections at the switch controllers a few time, and I've even disconnected the left rear controller.
I'll check the other door interconnects and give that a try.

I been through the fuse boxes a few times and couldn't find anything out of sorts there that I could find. All related fuses look fine.
I've never had any water intrusion issues inside and haven't seen any water inside.
Definitely a head scratcher.
 
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