The first sign of issues, the infotainment system started cutting out and restarting while driving. Then, on the drive home, I start experiencing mass electrical problems. Revs drop to zero, transmission cutout, loss of all systems. Stopping and restarting the car would fix things for a bit.

I swapped the battery, and same issues. I did a vehicle reset with SDD, same issues.

The infotainment cutout issues happen even if the car is not on.

Any idea on where to start for this?

2011 XJ 5.0 SC

 

Some pics

 

I had a drop out of the infotainment and some other items when the contactor for the start-stop system was failing. It appears to do a self test a few min after driving and the system voltage drops. there was a clattering sound from the right rear of the car when it happened. Just pull the ground cable from the little battery to disable the system as a test.

TJ

 

I did read that as a common issue, however my 2011 does not have that system.

I'm thinking of replacing the navigation unit as problems seem to start there, but why would that affect the car so much that I loose the engine?

Battery was swapped with a 3mo old one and runs between 13.5-14.2 when driving

 

You are lucky you don't have that system! I wonder what the remote control switch code is?

TJ

 

Sounds like a grounding issue somewhere, perhaps?

 

Any chance it could be the alternator heading out? I went for a drive today and now my scan tool was reading 11.7-12.1V while driving, which is considerably lower than it usually is. Again this is a newish AGM battery (swapped from another car) so I've already crossed off that. I had a a stall or two, but this time no funny business with the radio

 

Maybe? All the codes are U codes which are network codes. Those almost 100% of the time are related to electrical problems like the battery so yes the alternator could be causing it. But the alternator also has a bunch of codes and your not getting any alternator codes right now?

Have you cleared all codes and ran the SDD again?
Any chance you can try a new battery? I know you have a good one but we have seen mountains of problems solved with a battery replacement.
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No alternator codes, and I did a full sdd reset with code clear. I have a battery charger that has an alternator test. It failed the alternator test, for whatever that's worth. So I have a new alternator on the way, to be sure.

 

OK good progress but that is puzzling that SDD found no alternator codes yet your alternator tester did?
Let's hope it fixes your problem. Now one other thing is we have had reports of replacing the alternator and it's working fine but the car still throws an alternator code.
Are you getting yours rebuilt or another unit altogether?
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I have a rebuilt OEM unit on the way, and should be able to do the swap this weekend and find out

 

I also have a 2011 XJL SC, but it hasn't had any issues. However, my weekend car is a 2009 Aston Martin Vantage, and I was having similar low voltage electrical issues with that car. The whole car shut down like yours did while driving. I bought a new alternator, expecting to replace it, but when I put it on a lift and started pulling panels to inspect everything I found a terminal post with no nut on it, meaning the primary power return cables for both the alternator and the starter were barely making contact with each other. See photo below. I put on a new M8x1.25 high-temp zinc flange nut and it's been running great ever since.

Both of these cars were made by the same company, within a couple years of each other, both with similar Denso electrical systems. If this is a problem on one it may be a problem on the other. Inspect all your main power cable connections and grounds, especially the ones on the alternator.

 

I replaced the alternator and no more electrical issues. I had my intake fail at the same time, oddly. But fixing both has resulted in a smoothly running XJ again.

 

Thanks so much for reporting back! Glad to hear the alternator fixed it.
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Thank you, Clubairth - this is a very good post of yours on alternators that I have read you post elsewhere also. As in, what is causing the alternator problems and does an ' "aftermarket" cause a lot of problems' to quote you in another post... I have read Brutal on the x type forum saying the cables are often bad due to high internal resistance. I wonder if that also might apply to the X351?