Hello all,

I need some help so I decided to crowd-source it. I have a 2018 Jaguar XE(Gas, turbo). I purchased it "new to me" from the dealership. Ive had it for almost five years now. Ever since I purchased it, there would be intermittent times when the vehicle would enter limp mode. The first pattern I could assign to it was on cold starts on cold days. I would get gearbox fault, then amber-restricted performance, then red-restricted performance. When I made it to my destination and was ready to leave(minimum 1 hour later), the car forgot all about the headache it was putting me through. The first couple times this occurred, I schedule an appointment at the dealership, and of course, it was on its best behavior and they couldn't find anything. Since its an intermetant issue, my urgency fades and I somewhat believed its "cured" while holding onto the fear that it will come back as it has before. I finally purchased an obd2 scanner and I got the U0121 error code. I've told the dealership this and they still were unable to find anything that would cause this. What should be the next steps I take? I am looking forward to getting my hands dirty with the right guidance, of course.

Thanks in advance

 

Quite often intermittent electrical faults are the result of a failing or weak battery.

Use a voltmeter to check the available voltage with the ignition in the OFF position. There should be a minimum of 12.6 volts available for all the modules to function correctly. If the voltmeter indicates less than 12.6 volts, charge the battery for five hours at 2 to 5 amps and retest.

If the battery is the original one that was installed at the factory, it probably needs to be replaced.

 

it came up to 12.53 at the battery

 

Ended up taking it to Autozone to get a battery scan check this morning(engine light off, car running normally). They echoed your message that the battery needs to charge but the battery and alternator are good. I don't understand how the battery can be "good" if its not holding its full charge. Is this just an early sign of needing replacement down the line?

I have one car and no way to charge at home so taking the batter out to charge will prove problematic(but I guess less problematic than having the car shutdown on the highway). Im guessing its not work replacing the battery now until known for sure? Once I saw the car was running much better without any service lights I tested the voltage and it was at 13.6

 

Well, if you were to get a new battery, our first bit of advice would be to charge it fully, as they generally don’t have a full charge. But if you buy a new battery, you could get a charger with it, and charge it at home somewhere before installing it.

You could also drive your car for 30+ minutes, then measure the battery voltage with the car off.

 

You don't need to take the battery out of an XE to charge it if you use an intelligent charger like the CTEK.
You can use the charge points under the bonnet/hood - no need to get under the boot/trunk floor where the battery is located. The positive charge point is under the red cover on the RH side of the engine (looking forward). The negative charge point is the stud bolted to the RH side suspension turret.

 

Flawless logic, plus I should probably have a battery changer on hand anyway and its cheaper than a new battery to begin with. Will update after home charge.

 

Yes sir. Understood. Just didn't have a mechanism to charge it. This will shortly be resolved. Ordered a charger to do this. Thank you!

 

Firstly, I agree with previous posters that a failing or partially discharged battery is the number one suspect. Spurious error codes and warning messages are a classic symptom. On a 2018, the battery is in its sixth year if original and this is reasonable time to expect it to need replacement.

Secondly, I'm not one to have a go at Jaguar Dealers but yours has not handled this satisfactorily. The code U0121 is lost communication with Anti-Lock Brake System (ABS) control module. If nothing else, they should have done a battery test.

Recent Jaguars models use extended diagnostic codes which a simple code reader cannot detect but there are only two and both indicate an ABS signal, harness or ground fault:




I'll be surprised if a new battery (fully charged before fitting) and use of a CTEK or similar in future does not resolve this issue but if it doesn't, you have this decode information to troubleshoot it.

Graham

 

Thanks for all the great information. I was able to fully charge the battery. Here is the data:

12.71v at 12:24 pm - just after full charge (No warning lights)
12.6v at 01:30 pm - cold staft, started and a couple engine revs (No warning lights)
12.73v at 03:30 pm - wasn't started since 01:30 check. Started the car, did a couple of revs, turned it off, took measurement. (No warning lights)

Also forgot to add that I have not driven the vehicle at all today.

 

Thanks for this. I cant recall changing the battery for this vehicle. So it wouldn't surprise me as well if that was, at least, the failing culprit here.

 

Thanks for all the great information. I was able to fully charge the battery. Here is the data:

12.71v at 12:24 pm - just after full charge (No warning lights)
12.6v at 01:30 pm - cold staft, started and a couple engine revs (No warning lights)
12.73v at 03:30 pm - wasn't started since 01:30 check. Started the car, did a couple of revs, turned it off, took measurement. (No warning lights)

 

Were these reading taken with the ignition in the OFF position?

 

The car was off(yes, the ignition in the off position). doors closed. I just left the hood up and went out periodically to get the readings.

 

Did a 30-minute drive last night. Other than that it has been parked/off.
1224 pm today volutage reading at 12.43v (car completely off)

 

Hey all,

so I ended up taking it to the dealership. I was "informed" that the U codes are typically BS codes and that I should wait until there's actually a P-code ("actual problem") or spend some obscene amount of money trying to track this down. This didn't sit right with me. It's been too often when I'm driving at highway speeds and it enters limp mode and the only thing, in no traffic, that is keeping people from honking is the momentum of the car. Since its an intermittent issue, I can't predict when it will strike again. I told them it doesn't happen when I keep the car charged, and I was congratulated for charging the battery frequently. But this is an extremely inconvenient "fix".

 

Decided to just do a bettery swap and not all the codes are gone. Thanks all for the instruction

 

Editing my previous comment for clarity. Decided to replace the battery with a new one and NOW** the codes are gone.

 

I replace batteries every 4 years. Cheap piece of mind.

 

Sounds like a good idea. I hoped all those computer systems on the car would at least trigger a battery warning light. Insult to injury, I purchased a 2018 model in 2020 and between then and a couple weeks ago, I know I didn't change the battery. I assume the dealer wouldn't change the battery on a two-year-old car either. So a 4 year change cycle would have certainly cleared the assumptions.