Today when I walk to my 2012 xjl pull the latch ,nothing happend. So I went back took another key with me. still nothing. My gut feeling not the battery in the key fob dead ,it's the battery in the trunk. I went to open the drive door with the key, open the hood, patch a charger on the stud as the manual told. Suprisely, it showed 12.3V on my charge. Now I got frustrated. Battery is well, but car is dead .whatever you push the start/stop bottom, nothing. then I sit and play around. the radio works, rear entertaiment screen lits, windows can roll by press the same door button.but the driver's door can't control passage's window. seems like communication problem on the can bus. Try to open the trunk, I began to disssamble the rear seat. I found the foot well at the rear right side is so wet. there is a paddle of water. any ideas ? where the water is come from , most important thing , look like my CAN line is down, no other water leak sign other than the rear right foot well ,bcm feel dry too. My plan is Trying to dry it by open the rear door everyday ,wish me luckyly after water vanished the communication can recover any I can drive to someone to inspect the leaking. It's hard to tow my xjl cause I park a ackword place. peace: )

 

Check the sunroof drains, they can get clogged and flood the interior.

 

With 12.3 volts, your battery is not well. When the car is off and fully charged, a healthy battery will show at least 12.6 volts at rest. Readings below 12.4 volts indicate low charge or a weakening battery, while a voltage around 11.8 volts or lower suggests the battery is dead or critically low.

You should use a 10 Amp or higher battery charger (do not try to use a trickle charger or a battery maintainer - they don't have enough amps).

You're in China, but in the USA many national chain auto parts stores will load test a car battery for free. Just wondering if China has the same type of auto parts stores.

If your battery is more than 4 years old, I'd replace it.

 

Agree with Stuart. Your battery is NOT well.
Start by replacing it and see if that helps things.

After that it will depend on your capabilities? Can you DIY anything? If not your only choice is to take to a dealer.
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Thank you Stuarts, My battery is not good, it's 7 years old mabye. It works well 3 days ago. So I tried to diagnose it. first of all , I try to use a OBD2 scaner Launch x431 to make a full scan. Found out at medium speed can line ,all modules are talking except BCM. at high speed Can line .only the instuments and epb module are talking. So I examined the resistance of 6 14 and 3 11. it's all good at 60 om. It seems the Can bus are all good as well. Pull out my osiliscope , although the car seems dead, the medium Can bus(3,11 on obd plug) has activities when I press the key fob botton , but nothing on the high speed Can line. Then I checked the power and ground to the BCM , It's all good .So I think the bcm may go bad. booked a used one ,it's on the way .hope it works.

 

I opened the sunroof ,looking arround , the whole rail is dry and clear ,can't find any hole or drain , So where to find the drain pipe and clean it on those xjl

 

Can you post the codes? Did you have the car hooked up to a regulated DC power supply NOT a battery charger when you scanned the car? It's mandatory that the car be at full voltage when doing these scans.
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There are no codes stored in BCM ,cause the BCM don't communicate at the first place. some modules said lost communicating with BCM. So after examined the Can line make sure it is good . I bought a used BCM online. It's very cheap here. 600 Yuan, less than 100 box maybe.Yestday I replaced the BCM with the new one. Comm recovered. trunck works, glove box works ,even the doom lights and the instrumnent light up. Now it needs proggramming. But my sdd doesn't work , the JLR service is down . Now I am waiting for the rented autel online , So I can programm it without JLR service .I think my my cat will wake up soon.

 

Finally ,My x351 fired up . After replaced a second BCM. The first one is not good . AFter programmed ,every thing functions except crank no start. Scan shows some internall faults. Have to waiting for another Bcm delivered. This time it worked . oh, by the way . battery is weak , cause the first bcm crank no start ,I crank too many times. it has 9v left . So I charged it to 12.6, now it's good .after 7 years ,the battery still works fine.

 

@paddy_jee Your battery is NOT GOOD. It is 7 years old and has recently been completely dead. Even though you recharged it, after a battery has been fully discharged it will never reach its full capacity. A 7 year old car battery is past its useful lifespan.

It's your car, your money, and your choice. But don't say that you weren't told to get a new battery when your XJ won't start.

I'm pretty sure your 2012 XJL uses a standard "wet cell" battery. The AGM battery was introduced with the 2013 model year "Stop-Start" technology, which requires an AGM battery.

Click CAN YOU REVIVE A COMPLETELY DEAD CAR BATTERY?

 

Thank you Stuart S telling me the information about battery sufation recover. After a hard diagnose myself for about a week . The car is working again . consider the life time of the battery , maybe I will replace it after 1 year of before the next winter time . Now I am focuing on the leaking problem . It's so hard to maintain these old jaguars.