Is there a way to know for sure before replacing it? I've been reading a lot on these forums, and I've read of similar issues caused by TCCM, brake switch, brake light bulbs, ABS/speed sensors, dash cluster, corroded wires in passenger floor, thermostat sensor, etc. How can I diagnose with more certainty? I may be out of my depth on this one.

 

There's a Land Rover salvage yard near me. Can I swap in a used TCCM without programming it, just to see if it throws the same codes I've been getting? I can get it programmed before starting/driving if necessary. Thoughts?

 

UPDATE: Cascading faults gone!

What I've done:
-Took out passenger side seat, and cover over wire loom on passenger floorboard. There was an inch of standing water in that channel. Vacuumed out. Opened up one splice at red wire, and it looked pretty good. No corrosion. Still need to do driver side. I've been running space heater and dehumidifier inside non-stop for about a week now.
-Took TCCM to electronics repair guy. He couldn't see anything obviously wrong.
-Reinstalled TCCM
-Hard reset
-Only errors on dash are "Bonnet Open" and "Low Coolant"
-Started fine.
-Compressor ran for a minute, then shut off. "Suspension Fault", "Special Programs Unavailable"
-Battery showing 12.6 volts before start, 14.25 volts at idle.
-Took it for a couple mile drive.

My best guess is the water in the passenger side wire loom was causing a short in a splice or connector. Letting it dry out for a week seems to have solved it for the moment.

Codes I'm getting now:

Confirmed:
P240B Evaporative emission system leak detection pump control circuit low
P2525 Vacuum reservoir pressure sensor circuit

Pending:
P240B Evaporative emission system leak detection pump control circuit low
P2525 Vacuum reservoir pressure sensor circuit
P0171 System too lean
P0174 System too lean

Any suggestions how to solve these? None of these codes seem related to the "Suspension System Fault". How can I diagnose that?

 

If the air pump runs, shuts off, and has that fault displayed, the pump is usually needing replacement. I bought my last one off Amazon, and has not failed since. There are some decent videos on the whole procedure from PowerfulUK on YouTube.

 

Thanks metaldog. The PowerfulUK vid was a big help.
Got the compressor off. Opened up the air dryer and didn't even have to remove the first filter to tell the desiccant is played out. I'm seeing rust in there. Just ordered an X8R compressor rebuild kit on eBay.

Also, when inspecting the MAF sensor I noticed a loose air intake connection just to the right of the MAF. Tightened that up, and so far P0171 and P0174 codes haven't come back. Progress!

 

Updates:
-Replaced driver side sunroof drain elbow. Was completely disintegrated.
-Found corroded splice in passenger side wire loom with two green wires into one green wire. Soldered, and now key fobs are working as they should.
-Pulled CJB to access passenger side sunroof drain. The elbow was dry-rotted, but didn't appear to be leaking. Replaced.
-Reinstalling CJB wasn't easy, but not as bad as I'd read about. For those trying to reinstall it, I found one trick that may be helpful with the two connectors on the back. There is an orange connector and a green connector. There is a lever that has to start in the upright position, and must be pulled down to lock the connector in place. I tied a loop in a piece of spare wire, with about a foot left on the end. If you first get the connector started into the slot, then fish the end of the wire loop over the lever, then use one hand to hold the connector in place while you use the other hand to pull the looped wire down and start the lever coming down, this seemed to work well. Then use your hand to make sure the lever clicks into the locked position.
-I rebuilt the air compressor with kit from X8R. After reinstalling and starting it up, It ran for a minute or less and cut off. Suspension fault. I quickly found a leaks at the hoses that plug into the red and blue connectors on the air dryer cap. I've ordered a replacement cap with upgraded metal fittings off eBay. Should solve it.
-After a hard rain, I notice I still have a leak somewhere. I suspect the pillar trim on the sides of the windshield. Pulled those off, found broken clips and tabs. Pulled all the clips out and taped the holes with gorilla tape. Will see if this stops the leaks, and I'll be replacing those with new.

I'm still getting the following codes:
P240B Evaporative emission system leak detection pump control circuit low
P2525 Vacuum reservoir pressure sensor circuit

For P240B I'm thinking either a loose gas cap or maybe leak detection pump needs replacing. Any other ideas? I have no idea what P2525 is. Is this related to the air compressor tank?

 

Give your intake tubing from the filter to the TB a good look over. Those are prone to getting small cracks with age which let's in air after the MAF and throws codes.