I don't have a wiring diagram in front of me currently, but seeing as how accisible the TCCM is, and with it being a pass-through for the HS CAN, before pulling it apart I would check both sides of the CAN from it's connector.

You will want to check each side of the bus, and should have ~120 ohms on each side. From the TCCM connector, check from Yellow/Brown to Yellow/Black(there are two of each, check the wiring diagram for which pins, if resistance is tested across the wrong ones, it will be open circuit, and check the other) If you have ~120 ohms across both sides, will be condemned. If either side is O/C(and you've checked from each Yellow/Black to each Yellow/Brown) you will be looking at that side of the bus having an O/C, or another component bringing it down.

Possible components that can cause this are:

Instrument Cluster
EAS ECU
Parking Brake Module
Rear Differential ECU(if fitted with locking rear)
Powertrain Control Module
TCCM
and ABS ECU

Most common wiring issue is the connector/wires above the LH frame rail directly behind the rear wheel.

 

Appreciate the help!

Using my Fluke VMM with the alarm enabled, I've been all over the car, including the wiring behind the LR wheel, manipulating wiring and connectors in hopes of seeing the resistance on pins 6->14 drop from 120 Ohms to 60 (alarm).

Just pulled the Instrument Panel for the 3rd time, and I'm getting 120 Ohms across pins 1->2 (completely disconnected) of the IP, which corresponds to 6->14 of the Diag. Port.

Would love to hear I've got it wrong, and my IP is fine.

I'll plug it back in and perform the test you suggested on the TCCM, which is pristine inside, BTW.

 

I'm getting 120 Ohms going from the TCCM toward the ABS Module, and Open towards the ECM. Can't figure out a way to test the ECM with wires connected.

Is there a way to hot-wire the air compressor relay so I can raise this beast? Would like to get at the wiring behind the RF wheel cover.

 

The IP (as well as the ABS ECU) has a 120 ohm terminating resistor inside, between the high and low sides of the HS CAN. By checking pins 6-14, those two resistors are effectively in parallel, giving the expected value of 60ohms. With an open in the wiring on one side, you get the full 120 of the side that is in tact.

Checking from the TCCM will tell you which side to look at for the open, which can then be checked from there to another ecu until you locate where the open is, and from there it will be physical checks of the wires.

 

You can replace relay 7 with a 3 inches of 12 gauge wire insulated in the middle , so you can insert it and pull it out safely and raise your lr3, assuming your compressor is in working order, BUT.. you have to be VERY careful not to let the compressor overheat and burn.It is a quick trick to figure out , if the air compressor works or not alone and not meant to be used to run it to raise the land rover.You do not need engine ON for this or even key in ignition. Compressor will fire just fine..
You will have to place a wire in two terminals , that are opposite to each other and are positioned differently , meaning one is horizontal and one vertical, they look like a de constructed letter T.

 

Do as above to raise, I prefer having the key turned on so that the system can still control the valves correctly.

To check from PCM back, you will want to do the same as at the TCCM(PCM is also a pass through)

 

Thanks Thorgal, roverguy7 (Dave),

Compressor runs, car won't raise, key
On or key Off.

As for progress on the module and connector testing,
I've narrowed it down to somewhere between the ECU and the ABS module on the Yellow/Brown wire. I'm getting 1.5 Ohms resistance on Yellow/Black between the IP and the ABS, 2.8k on the Yellow Brown.

2 things really slowing me down; inability to raise the vehicle, and a diagram
Showing the location of the various modules on the HS CAN Bus.

 

Yellow/Black and Yellow/Brown are the same thing, one is high side, one low, it's a redundant bus. What you have by the last post, means that the issue is with the Yellow/Brown, but as above (with 120ohm on the side to ABS from TCCM) your issue should not be towards the ABS.

I would be looking at the connector at the rear frame, as well as the harness that crosses over to the parking brake module.

 

So I've narrowed it down to something between pin 57 of the ECM and pin 2 of the Center Console Switch Pack, which leaves the Rear Differential Control Module and Parking Brake Module plus interconnects. As roverguy7 suggested, I went over the cables and cleaned the connectors behind the LR wheel. Can't reach the connector to the EPB Module, due to the suspension sitting on the bumpers.

I called a local shop, but they will not allow me around the vehicle at all when it is on the lift.

Could really use some help to get this thing elevated. I'm positive the air suspension is in good working order, it's a matter of getting the air from the tank into the shocks.

 

Of all the professed capabilities of this vehicle, "Start" is not one. For this it has earned my contempt. Land Rover has lessons to learn...