2012 LR4 HSE with ~75K miles. Noticed a small coolant leak in late spring that worsened this summer. I parked the truck in mid-July, ordered parts, and read up on the repairs. I've done a fair bit of automotive repairs over the years, but nothing on this truck in 8 years other than brakes.

I replaced water pump (+tube), front crossover, rear pipe, thermostat, and serp belt, primarily following the sticky thread guidance. Also referenced crossover-specific thread and a video(*). A few threads listing parts were helpful, but I don't have the links handy.

Being out of practice I made a likely fatal mistake [in hindsight]: I did not disconnect the battery lead before proceeding. While possibly not critical if doing only the water pump, the pipes require removing the manifold and throttle body, and their associated electrical connections, etc. My son was around for part of the repair and we did manually push the throttle body's butterfly valve.

My first problem: upon reassembly and restart, the truck immediately lit up with warning lights and codes for restricted performance mode as it hunted for a proper idle. Notable codes included P0122 [TPS A circuit low] and P2135 [TPS A/B voltage correlation].

I don't have a proper diagnostic tool [yet]. I tried non-tool methods of resetting the idle (timed on/off sequences, fully draining the electrical system, etc.). None of it worked.

New key problem: while trying the above sequences the positive battery lead got hot and melted the battery casing under the cable fuse. So I can't run it for long in restricted performance mode before shutting it down to let it cool off.

Last week I had it towed to a local euro indy shop to reset idle adaptations. Yesterday I decided that I'm pulling it from the shop and embarking again on fixing it myself. They were struggling with parts availability on items I can seem to locate and I'm not confident they ever actually tried to reset the adaptions. Regardless...

It now has new battery and a new positive-to-fuse-box cable.

My general plan:

1. purchase a gap/iland/icarsoft tool
2. test battery lead for resistance (or whatever). replace if necessary (LR020137, or possibly just the positive cable fuse)
3. test alternator. replace if necessary (LR065246)
4. reset adaptions with diagnostic tool
5. if that doesn't work, replace the throttle body (LR010814)

Current throttle body "looks" fine, despite the fact that I may have fried the controller during the repair.

So... [thanks for reading btw!] any helpful thoughts or guidance on the above? The hot lead and hunting for idle are my main problems. I'd clearly like to minimize the parts I throw at it, but here I am.

Suggestions on which diagnostic tool to get? I'm primarily looking at Gap IIDTool or ILand V2. I also considered the cheaper iCarsoft LR v3, but it's unclear if it has equivalent functionality (to reset ECU).

Thank you!

* I originally linked the video, but didn't want the preview dominating the post.

 

While I agree that disconnecting the battery is the cautious thing to do, I don’t see how that would have caused your TPS problems unless you actually shorted something while doing the repairs. Just disconnecting the throttle body (or any of the electrical connections needed for manifold removal) while the battery is still connected should not have done any harm as far as I’m aware (I’ve done that myself).

Likewise, moving the butterfly manually should not be a problem - but do be sure there is nothing left there interfering with its operation. Even a little gunk on the throttle body can cause that butterfly to stick a little bit or fail to close all the way and throw everything off.

I think the very first order of business would be to check the battery itself. If the battery is fried, you’re not going to get very far diagnosing anything else.

How long was the car down for? I’m just wondering if it sat for a long time without anything charging it. If the battery were already weak, and it discharged too far while sitting, that could cause overheating when the alternator kicked in and ramped up. Resistance at the lead would be another thing to check, as you mentioned.

What other codes are you seeing?

As for scanners, I have the Gap IID, which is great. I don’t know anything about the iCarsoft for this car, but I have one for a volvo - haven’t used it too much, but seems to have very limited functionality for the $200+ I paid for it.

 

The battery disconnect theory was me trying to isolate why it was confused when re-started after repairs. It's possible the throttle body was not in a neutral/home state upon re-assembly, but unsure. Thanks for clarifying that is an unlikely cause. That's helpful.

Battery is now new. I've not confirmed it's health though; just assumed it would be good. The original sat for 7-10 days while I awaited parts. I did not start it before commencing repairs.

Only other initial permanent code was a P2105 [Throttle actuator control system forced engine shutdown]. At one point it did throw P054B and P054D [cold start 'B' camshaft position timing over-retarded bank (1 and 2)].

Thanks for the diag tool thoughts. I've largely settled on the Gap IID. The iLand fine print said something about only providing 3 years of use before its capabilities "expire" (or something).

I'm waiting for the truck to get towed back this aft, so can't confirm the voltage numbers right now, but it's wild that the lead is getting so hot. I was wondering if somehow the idle variations were confusing the ECU or alternator (or something in that chain) to send too much voltage.

 

I understand now - you were thinking that maybe the butterfly was in the wrong position when it reconnected to the ECU - so it recalibrated to the wrong position. But the butterfly on your car is spring loaded, correct? (I have the 3.0 v6). So it returns to idle unless something is blocking it. At any rate, not sure how the recalibration works on the car, but with the GAP tool you can reset all the adaptations, and I seem to recall resetting adaptations has helped with tps problems for other posters in the past.

Since you had it unplugged and moving wires, etc., my first thought would be a problem with the plug or wiring harness on the throttle body. There is another piece to the system, and that’s the throttle pedal position sensor at the throttle pedal, but since you were working in the engine bay, I’m thinking that’s less likely.

The battery lead getting that hot is concerning, and I don’t think anything on the car should be pulling enough amperage to cause that (other than the starter, but that’s only running for a few seconds). So, thinking either resistance at terminal, short circuit, or bad battery or alternator.

Just to clarify - you put a new battery in before doing repairs. So the battery is new. I don’t think this should really make a difference, but you are supposed to calibrate the battery module with a new battery - regulates the amount of charge put in, and specifies the type of battery (AGM or not, size H7 H8 etc.). But plenty of people skip this step without overheating.

A problem with the voltage supply can put the car into restricted performance - and that p2105 code is how the car does it. I like theories that tie everything together, so it’s possible whatever happened at the battery side is causing the tps problems.

Hopefully some others will chime in. I’ll encourage you to post up at landroverworld.org as well (and search those threads too). Sometimes you’ll have more activity on those forums.

 

i recall reading a thread that sounds very similar to your situation. The guy had connected two plugs on or near the rear pipe incorrectly. The two plugs are in the same area and are the same size. I recall that the two plugs are on in the area of the rear passenger corner of the engine. He connected them correctly and his issues cleared. It might be something to check. Phil

 

Thanks, Phil. I too saw a similar thread when researching (this one?). Thanks for chiming in with the reminder. I'll confirm they're connected properly.

@jlglr4 I now have the truck back. The old battery was indeed quite low, so as you noted upon initial restart that could have caused a cascade of issues as the system tried to charge the battery.

I suspect the fuse on the top of the positive battery cable has failed. It's the primary/only source of the heat. There is a ~.3 voltage drop across the fuse. I measured with a multi-meter on some exposed cable below the fuse, comparing it to the reading right off the terminal. Lucky8 sells just the fuse, so I'm planning to try that first. LR sells the complete positive cable with the fuse included, but given a lower part price and a rather easier repair that's the current plan.

The shop supposedly did the battery coding, but I'll confirm with the Gap tool. Fwiw, I'd never done that in prior battery replacements. "Today I learned..."

Once the tool and fuse arrive I'll be in a better position to diagnose further issues, so I'll wait before messing with the throttle body any further.

I'd considered cross-posting on the LRW forum too, but wasn't sure how that'd be received. Thanks for the guidance there.

 

I've replaced the fuse on the positive battery cable (part from Lucky8*). Initial take is that this has solved the excess heat issue. No more voltage drop across the fuse in the positive battery chain. [Fist pump emoji?]

image comparing failed fusible link [top] (installed at upper end of positive battery cable) with new part [bottom].


Reset adaptations with the Gap IID tool. Restricted performance warnings persisting. Removed air intake to find obviously disconnected lower wire in the throttle body connector. I don't have post-assembly pics, but was not visibly broken in images taken after TB had been removed. Alas, now to figure out if I can disassemble the connector to re-solder the wire.

images showing the disconnected throttle body connector wire

 

That’s great news (not that you have a disconnect, but that you found the problem). That shouldn’t be too tough fix. Lots of videos showing how to de-pin all various types of these connectors.