I have a 2010 LR2 (gasoline) that has some electrical codes. I've replaced crank and cam position sensors, MAF and MAP sensors, the throttle body, and accelerator pedal. After most of these I thought I had it fixed but it keeps coming back. Current codes are P2138 for throttle/pedal position sensor and P0642 Sensor Reference Voltage A Circuit Low.

Some internet and AI searchs lead me to check the APP signals using an OBDII reader because it seems P2138 means the D and E signals don't match. Viewing live data for those two show that D is steady at about 7.1 and E fluctuates between 7.8 and 8.1. I read that they don't need to be exactly the same but should go up and down together so the fluctating is not good. That lead to replacing the gas pedal (which didn't fix it) and the throttle body (which didn't fix it).

Right now I'm wondering if the ECM is bad.





I found a manual online with some wiring diagrams. It shows the wires to the gas pedal labeled with what they are and their colors. Electronic Engine Controls (Sheet 2) — 2010 Land Rover LR2 (LF) L6-3.2L Service Manual | Operation CHARM (see above). I unplugged the pedal and checked voltages at each. Wire 1 was at 5.1 volts, wires 2 & 3 about 50 mV, wire 4 is ground and has continuity to ground, wires 5 & 6 had just under 12 volts. I know at least one wire should be about 5 volts for a signal but I don't know if these are correct. Does anyone know what each should read?

Any other suggestions of what to check or look at? I did see some threads mentioning alternators. Could a faulty alternator be the issue?

 

Don't know specifics, but yes it could be ECM. Have you disconnected and reseated the main ECM-end harness connectors? Could be as simple as that (Be Gentle!). I'd also inspect the ECM as best you can for corrosion (especially if you're in a wet/humid climate).

Also could be harness or connector issues to the devices. Might pin out OK while shutdown in the driveway but not make good connection, or fluctuate with driving vibration. If you narrow it down to one or two specific components, you could always just make your own sub-harness with new connectors.

Check the harnesses for rodent damage, I had that happen on my LR2 even though it was a daily driver in an urban metro area

Yes a bad alternator (or battery) could do all sorts of weird things with this car, but my gut feel is that it's not that. You can use an OBDII tool to monitor or graph the alternator performance while driving, using the AC, etc and see if looks normal.

 

The alternator pulley is known to seize and give you similar symptoms. Check out freel2.com, it's a good resource in general.

 

I have disconnected and reconnected the ECM connectors with no change.
A problem with testing the alternator is it won't even start right now. The dash says Engine System Fault. I thought it would go away after resetting codes or unplugging the battery (that has worked with the previous repairs) but this time it won't. It will crank and turn over a few times on its own but then die and then only crank.

I have inspected the wiring I can see and have removed, cleaned, and reinstalled any electrical ground connections I can find. I guess I will try testing continuity in the wires. I previously found the harness going to the transmission control module had damage to insulation and rewrapped all wires in electrical tape. (At that time I thought that was my issue.)

 

I will inspect the pulley when I can, but as I mentioned in another reply, I can't get the engine to run right now so it's difficult to test the alternator.

 

The one thing I don't see if if you tested and/or replaced the battery. This vehicle of ours does very weird things if the battery is not in perfect or near-perfect condition.

> ...wires 5 & 6 had just under 12 volts.

Anything that is carrying DC voltage coming from the battery should in theory have the same voltage as if it had been measured at the battery. I think this here's your sign.

 

The battery has 11.9 volts and wire 6 is measuring 11.8 volts. I'm not too worried about that as the wiring diagram shows it going through some relays and controllers to get to the pedal.

 

Is there anyone who has an OBDII scanner tool that shows Live Data and could plug in to their LR2 and tell me what the APP_D and APP_E signals show?

On mine, with the pedal not depressed at all the APP_D shows 7.1 and APP_E fluctuates between 7.8 and 8.2. I think this is showing what code P2138 is telling me, the signal D isn't matching signal E. I just want to confirm that and wonder what a functioning LR2's live data shows.

 

Well, let me know when you rack up 50 years of experience with analog and digital electrical systems like me.

Your battery needs to be replaced. I'm out of this thread. Good luck.

 

11.9V is too low. Could be because you've been trying to start it, so it needs to be charged thoroughly at the very least.

A bad (or even slightly weak) battery will cause problems with this car, when you crank the draw is heavy enough that it drops system voltage so low that it confuses various computers.

If the battery is 5+ years old, just replace it. If it's a wet cell and has not had regular maintenance (top off with distilled water), just replace it.

Otherwise remove it and take it to FLAPS or a shop for a professional charge and test. I'd say it's a waste of time to troubleshoot these kinds of issues on an LR2 unless you're sure the battery is solid.