07 LR3 4.4, At my wits end trying to diagnose this problem for 6 months. Issue started happening 3 months after A/C bearing went bad and caused the serpentine belt to come off. Fan harness seemed ok, wasn’t cut, just separated the plug.

Car starts fine from cold, everything works normally (except radiator fan running all the time). After 15 minutes, cluster lights up like a Christmas tree then goes black, all gauges to zero, voltage surges to 17.5 volts or more (codes P063D-00 and P063C-00 present) Once this happens, if you try to restart the car, often the shift lever gets stuck in “Park.” Eventually after waiting a minute or so, truck restarts and drives normally, then everything recurs again.

Here’s what I have done:

Major electrical related fixes I've done (and a lot of other things not mentioned). New alternator (replaced twice) with new pig connector, battery, radiator fan and clutch, sent cluster ECM and TCCM out, all clean and working no corrosion whatsoever, new MAF, fusebox under hood, brake light switch, rear bulbs, cleaned all grounds under front wheel wells and under hood/against engine. Removed fusebox under glovebox to check for water intrusion from sunroof drains, all clean. Anyone know what I'm missing here? Thanks in advance.

 

What a nightmare!
I'd first want to troubleshoot that continuous fan issue. Whatever is causing that could be the source of all your problems.

 

Oof, this is odd and scary, particularly the voltage spike. I'm trying to wrap my head around that ... Do you have fuses popping? If so, check the components on that circuit.

The rad fan harness may not have physical damage, but I'm guessing the belt pulled it out by the wires. You may have a separated terminal in there that prevents the fan from being regulated. The connectors have a little door you can pry open on the front or back, then pull the waterproof grommet back with some tweezers, and finally use a depinning tool to extract the terminal+ crimped wire from the harness for inspection and continuity testing. It's obviously important to keep those wires in the same circuits, so I would take pictures and pull them out one at a time.

For voltage, do you have more than one battery? The max supply of the battery is somewhere around 14 volts fully charged. If you're getting more than this, either your battery or to alternator is freaking out. I suspect the alternator even if you replaced it already. Those extra volts have to be coming from somewhere and I don't know anything else on these vehicles that creates or stores a large charge.

Lastly, since your issues are after the car is warm, I'd take a close look at your battery cables and routing. Make sure there is no damage and nothing shorting out anywhere that would shut the vehicle off. Try feeling the cables after 15 min to see if they are hot and over used. Wires and cables get hot when given too much electricity. Replace then if they are hot.

Edit: additional thought- I read you've replaced the alt twice. You've probably done that several times because people suspected it and convinced you to replace it. Did you get a Denso unit? The voltage regulator on the alt is designed to prevent voltage spikes like you are having. Occam's razor, this is your simplest solution to the overvolt issue, even if you've done it twice now.

I've had new aftermarket alts test fine, but still had issues. I've swapped a new alt three times before on a LR. The aftermarket alts were in stock or fast shipping, but they didn't fix my undervolting issue. I learned this by swapping the voltage regulator off my old unit onto the new aftermarket alt. It finally worked, so I swapped it one last time for a new Denso.

 

update
Installed new starter, checked and cleaned starter cable from battery. Purchased new ECM and had it cloned. Replaced alternator with OEM. Problem still there
kels83 i will check the radiator fan plug to make sure no separated terminals. I have a single battery, same one I have always used it 1000 CCA since i am also running a 12k lb winch. Battery is new also voltage 12.7v.

I will also check the alternator wire although the alternator fuse in the fusebox is working properly.

 

UPDATE: I checked the radiator fan plug wires and all checked out good. I ran the car in my garage until the voltage spiked to 17v causing the dash to go out completely. While the car was running, I removed the PIG connector on the alternator and low and behold THE DASH TURNED BACK ON AND THE VOLTAGE DROPPED BACK TO 13.8V!!! It seems that I have located the short. The Pig connector has 3 wires...white with green stripe (positive on left side or plug), White with red stripe (negative in the center of plug), and Brown (positive on right side of plug). The PIG connector goes into the main wiring harness then to the ECM? Which of these 3 wires in the PIG connector is the exciter wire that adjusts the voltage? not sure where to go from here.

 

Did you locate the fault on the circuit. Having the same issues with my LR3.

 

I had a battery light on and off and the fan running. Then replaced the alternator with a bosch unit and a new AGM battery. After this i saw charging at 15,8 volts but no faults so decided to run with it because after some time it dropped to 14,9 volts. After 1000 kilometers it has stopped charging... I tried to make a ground connection from battery post directly to engine, but no changes the car will still not charge. One thing i noticed was the 3 pin plug connection on the alternator was upside down on the bosh unit and a pain to connect but not sure if this has something to with it. LI/RC/BVS seem to be in the same order as denso unit, so it should be okay i hope. Does any one know the voltage measures on the single cables on the pig connection on alternator..? Or maybe the terminal numbers to the ECM to measure continuity..?
Best regards from Sweden.

 

You want to stick with a Denso alternator, anything else will cause issues like your overcharging.

 

15.8v? How is the truck not fried.... wow....

 

I have a brand new denso alternator in the mail and a new yuasa battery also (non AGM). In the mean time Ill check ground connection and continuity on batt sens and duty cycle values on alt com / alt mon wires to establish what output the ECM is expecting from alternator. Last i will try to unplug the three pin connector and see if the alternator will go into safe fail mode and produce the 13,8volts.