Hello,

My 1999 XJR has been acting strangely since last week. I have been doing diagnostic work, but lack the electric diagrams to find the common denominators to my issues, currently my only resource is the X308 workshop manual which is quite easy to find on PDF but it doesn't seem to have all the diagrams and they are scattered across the document. I suppose I could find them all in JTIS but I don't have access to it.

To the problem: when I turn the ignition on, several systems aren't getting power. I get 3 messages: "electric anomaly", "suspension anomaly", "restricted performance" (if the messages are not accurate, it's because I translated them from French. When I have a moment I will try setting my message center to English and give you the original English language messages). If I try to start, the car will crank but won't fire. The systems I have noticed not getting power are:
-Engine management or part of it, highlighted by the fact it won't fire and the restricted performance message
-CATS suspension (based only on the "suspension anomaly" message)
-Most of the cluster warning lights - it seems the ones that don't work are the ones related to the engine and traction control
-A/C (no power to the A/C control panel and the fans)
-Outside lights

Maybe there are more systems that don't get power and haven't noticed. I have checked the fuses and relays that seem to power one or several or those systems and everything works. The battery is charged and in good condition. I checked the wiring around the ignition switch.

The strange part is that when this issue comes up, I will leave the ignition on and all the power will come back suddenly after one minute or so. Then the car will start and drive fine, the problem won't come back for several hours usually. When the issue is gone I have tried replicating it by unplugging various fuses and relay with the ignition on, but none will have that exact set of symptoms one disconnected.

If I had access to complete wiring diagrams I would look for the common denominator to all of those systems, but I don't. The problem happened very suddenly and it really looks like on of those ridiculous electrical issues that aren't much to repair but will have serious symptoms... Except if I have to replace a control unit somewhere.

 

You are correct - the Electrical Guide for your vehicle is available in JTIS.

As a newbie, you can't download attachments from the forum until you have passed the minimum period of membership and number of posts so I've sent the 1999 X308 Electrical Guide to the email address you have registered with the forum.

Graham

 

Thanks a lot for the guide. I will look at it and keep you updated on what I find

Edit: I started to have a look in the manual, I saw there was a general ignition + relay in the LH heelboard fusebox. I don't know why I did not see this before, but I checked it now. When I remove it while the car works normally it replicates the exact same symptom I described. Right now the car works as it should, I will wait a bit for the issue to come back and do some more diagnosis to see if the issue comes from the wiring or the relay. Given the symptoms (delayed activation) I think it's very likely to be the relay.

 

Despite your comment about the battery condition, these symptoms are classic signs of a failing battery, nearing the end of its useful life. The fact that the systems do come on after the engine has been running and for "several hours" afterwards suggests a direct connection with available battery voltage. How old is the battery? Is the car used on a very regular basis and for significant distance?

 

The battery is 3 years old, It's a Bosch S5 with peak current and capacity that are superior to the required specs for the car. It sometimes is not driven for a few weeks but when it does, I keep it on a battery tender.

I agree it looked like a battery issue, and that was my very first thought when the problem first appeared. Though having had battery issues in the past, the symptoms don't match: when the battery was low the first symptoms have always been a "traction control failure" message, dimmed dash lights and the starter motor that lacked power to crank the engine. Here some systems did not get power at all while others (including traction control) got the normal power level, even enough for the starter to run normally. Also the problem looked intermittent at first, and the first time it disappeared was after waiting without doing anything, which means it worked better with an even more discharged battery. Then my first action was to charge it, which didn't change anything. Also the issue doesn't disappear after the engine running, but after the ignition being turned on, even without running the engine.

It seems the ignition + relay in the LH heelboard fusebox was the answer though. According to the electrical guide GGG sent me, it is the one that sends power on key II position. As I said, removing it created the exact same symptoms. Also I took that relay and connected it to a test bench yesterday and powered it, it worked. Then I left it all night undisturbed to recreate the failure as it happened on the car, and this morning when powered it would not work right away but only after a minute or so. Just like the issue on the car. I left it connected to the bench equipment and will test it once more in a few hours just to make sure, but I am pretty convinced I found my culprit. I already replaced it with a brand new relay yesterday and the issue didn't reappear on the car since.