abran - not on an LR3. I have been on a few car forums over the years. I know of two cases where a PCM went bad on a Ford product, Mark VIII. It was when they moved to COP and the PCM fired the coils directly. The previous setup, using coils packs, were never an issue. And then with BMWs I know of one specific case with a 750iL that had a faulty PCM. The car had THREE mind you. One for each bank and a middle one to sync them up (V12 engine, everything was doubled - MAF, distrubutors, fuel pumps, etc). So its was a real bear to trouble shoot.

So I tend to agree than PCMs dont generally fail. The electronics in most cars are pretty good for the late 90s on up. I would say if its intermittent, its more of a bus issue - bad connections, grounds, power issues, etc.

 

 

I finally think I fixed the low battery problem with my second replacement alternator. Wow these are some finicky vehicles! Now reading 14.2-14.4 volts consistently )

Things that did not work:

• Replace all cables with 2/0 gauge (factory is 1/0, but why not upgrade?) at a cost of $120 US including a hydraulic crimper
• Replace 3-pin alternator harness
• Replace Automatic Temp Control Unit (ATCU) which can limit voltage in certain temperatures
• Attempt to replace engine control unit; DakotaTraveler is right, these cannot be replaced with used units but I did find a service to rebuild them for $400 (Rebuilt LAND ROVER Modules | AES Modules | Repairs)

I just wouldn't believe the 2nd alternator was bad after getting it checked out by a local alternator shop that gave it a pass. On a side note it appears a failing alternator will short and take down a good battery. LR designed the starter and alternator on the same cable, so when I replaced it I used two separate cables to isolate the alt-battery connection. I also added a 200 amp mega-fuse on the new alt-battery cable and any future alternator failures should blow this fuse, saving my $300 battery

 

Is factory really 1/0? I thought smaller. No matter though. I will be replacing all mine but with 1/0 (0 awg). 1/0 is ample for even a duel battery setup with winch, but I guess I wont be upgrading as you did. Thicker gauge certainly can't hurt! As fro separating, I decided not to. It was not cheap getting a crimp T fitting. About $50. Looked all over, only one place makes them (odd). The alternator is not really active in any way when the alternator runs. And when starting, even the alternator is not putting out (RPM too low). So having them "together" is not a big deal and simplifies the wiring.

I should replace my alternator hardness, happen to have a P/N? I've read they break very easily. And where is the ATCU? I am not having issue, but maybe for future reference.

 

Yup, the factory is 1/0 (0 awg). I started replacing the end lugs on some cables before replacing the whole cable. Yes 2/0 is overkill but i had extra cable from a project car. My setup is still working strong

Answers to your two questions:

• I don't recall the product number but the harness is denso and is shared with lots of other vehicles and the little locking "clip" on mine broke as you say to be careful. I attached some pictures of the harness that worked for me. Both amazon and ebay have lots of options if you search "denso alternator harness". I also got the grey harness with red+green+white wires but the terminals didn't have rubber boots and therefore were not sealed from the elements. I'd advise against that one. Also there is some info on the wire order at https://www.disco3.co.uk/gallery/thu...php?album=3801 that I found useful to make sure the wires are in the correct order. I'm looking at the old harness now with the "clip" on top (same orientation as the attached picture) and the order of wires from left to right is brown/green, white/red, white/green.
• The ATCU is the unit in the dash with dual climate control dials and heated seat buttons. I believe the brown/green wire from the alternator travels to this.