The Drive up
My son's LR3 has been in Montana for three years now. It's having issues that shop can figure out. They did a new altinator and Fuse box because of carosion on the board because of a sunroof leak.
I ended up taking him a jeep I had, I brought his LR3 home to California so I could try to fix it myself.
The issues: Yesterday, when it was rainning. The Transmission went into limp moad, The yellow suspension light went on, the yellow brake light came on and the check engine light came on. all at the same time. These are the issues that he was having before.
I was able to pull over and clear all the codes and it moved on ok with a no lights, until the the check engine light came back on for "Low Cat efficancy on bank one and two." and I think the cats are bad, this is a seprate issue because this has been happing for along time. Montanna deosn't have smog.
It's my beilf that there is a ground issue becaue it happen when I had the headlights on the wipers going and the A/C all on at the same time. but I'm really not sure. When I start it up frist thing in the morning it seems fine, I can drive it from 10-20 miles brfore the check engine light come on for the Cats. I did a smoketest yesterday and it had no issue except the EGR and I reseald that.
I would liketo look for a bad ground but not sure were to look. any help would be great.

 

no codes no help

 

When it happens again, I will pull codes. I had to clear them to get moving on the road.

 

Need codes as asked for but given the history with water, I would take 5 minutes and pull the door sill on the front passenger side and look at the wiring to see if it's still wet or if the splice (there's at least 1 critical splice) in that part of the door sill wiring has corroded. That's a common cause of issues, and if water it the junction box it probably hit the splice in the door sill wiring bundle.

 

You wouldn't happen to have a photo of that splice, would you?

 

It's under the sill cover and then under a wire harness holder (a black stiff plastic piece that I think is bolted in?). If memory serves, the splices on LR3 and Jaguars of the era are not particularly robust, literally just a soldered connection that is taped. And that tunnel contains key communication lines to the transmission, so all it takes is one bad ground or power splice to cause all sorts of chaos. Look for a taped where where from one side two go in and one leaves. This post addressed a different set of wiring issues caused by a bad splice in that location but in it you can see the bundle of wires and what you have to get access to: https://images.app.goo.gl/gwNiTo9df8LjnB3Y9

 

I pulled the seat out, the glove box, the fuse panel, pulled up the carpet and looked at all the connections by the fuse panel. I just can't find the smoking gun. What I did find was the ECU looks to have been replaced. The cover that holds it in, the tabs were broken and the ECU looks very clean. Also, one of the connections was broken on the handle that locks it down. I was able to fix it with some zip ties and then I used some scews to lock down the cover. I put dielectric silicone on all electrical connects. It fires right up and drives great and I can't get to act up again. However it's not raining here. I might need to give it the garden hose treatment.

 

Check your sunroof drains. They’re probably clogged or cracked(or both) If the windscreen has been replaced, there’s a seal on the passenger side that may have been damaged. Whatever it is, fix the leak first. If it continues to stay damp, the gremlins will keep coming back until something catastrophic happens. Corrosion from water leaks will kill any modern car
I’ve had pretty good luck hosing down wiring, connectors and electrical components with WD40 to help drive moisture out. I do mean hose it down, as in sop up the runoff off the floor.( Note: that’s its actual proper use. It wasn’t designed as a lubricant or penetrating oil)

 

Well, today it's raining, and the issues are coming back. I have looked under the dash, and what I can see is dry, and I can't find any moisture. The sunroof drain is working properly. I'm betting it's the windshield. It has been replaced because it doesn't have the heater element. I'm going to take off the cowling and see if I tell the seal is bad. I will report back what I find.

 

If you are going to remove the cowling, then you might as well make a little shield and adhere it to the box where the water ingresses.