I have a 1998 XJR. I love this car, but the electrical system is driving me nuts. When I get in the car the only thing lighting up is the security light. It is as if the battery were disconnected. If I disconnect the + battery cable, make sure the battery is charged, then reconnect it, everything works fine until the next episode. When this occurs the battery measures 5.66 VDC and 0.086 A, when connected and 14.1 VDC disconnected. I have spent hours digging through the elcetrical guide and can not find where this fault might be. OBTW the OCD indicates NO faults with the battery connected or disconnected. I talked to the service manager at the Jag dealer and he said he had never seen or heard of such a problem. I am betting on a faulty relay, but which one?
Don

 

A failing or weak battery can cause many unusual electrical faults. What is the age of the battery?

If the battery is charged, but has less than 12.8 volts when the vehicle is not running, it must be replaced.

 

Don,

I've moved your question from General Tech Help to X308 forum. This is the place to post technical questions about your model.

Graham

 

There are a lot of discussions on this forum and YouTube (use Google) to show how to hunt down electrical current draw when the ignition is turned off.

Try this first: with ignition off, put your cell phone camera on video put it in your glove compartment and close the door; then do the same thing with the trunk.

Surely, the service manager at the dealer was able to determine if it was a bad battery. (?)!

Glove compartment switches and trunk switches are often the cause.

Long before cell phones, I had a constant dead battery (s) in an old 2500 BMW. Stuck my young son in the trunk, told him to pound hard when it gets dark -- "lights didn't go out Daddy!" (He's officer in charge of a Navy SAR helo det near Seattle now).

 

I thought there were laws about shutting kids in boots (trunks), and sending them up chimneys! lol.

 

First of all, if your battery is fully charged and does not have an internal open circuit, then if it is dropping to 5 volts, there is a tremendous load on it! Like fire in seconds! So, if you do not smell something burning, then either you have an intermittent open circuit inside the battery OR (more likely) your battery post terminal is not making a good connection. Next time you read 5 volts, check the battery voltage right on the lead studs sticking out of the battery,not the terminal blocks, and see if you do not really have 12 volts there.

 

It is a brand new battery, so it was first suspect. Les swab checked and said new battery is good. They even beat on it to see if they could induce fault. I checked all the fuse boxes for a bad groound and found them all to be .001 ohms or less. You would think that a large voltage drop would indicate a huge current drain. Current drain with key off is 0.086A at both voltage levels which defys all my 40 years knowledge as a radar test engineer. In my 7 years of schooling to get my MSEE there was not a single class on electrical system Gremlins.

 

Well, Gremlins or not, you cannot repeal Ohms's law. So, what two points are you measuring voltage between when you read 5 volts?

 

directly on the battery posts. I talked with a man who had the same problem with a chevy pickup. Turned out to be a cap that was charging but couldn't discharge because of a cracked printed circuit board. Big difference was the OCD showed the fault.

 

You know, I really just don't know what to say except obviously it is Gremlins!

There are laws of physics and rules of mother nature that even Jaguars need to follow.

 

Since this is an unusual electrical issue, I'm going back to the basics. I do need some more info though.

1. How long ago did this first happen?

2. Are you parking on an incline/decline when this happens? I know this seems like a silly question but, these subtle clues help out sometimes.

3. How often does this occur?

4. Since I don't know where you live and I can't assume anything even though it's only March, I do have to ask, does it seem to happen more so when it's hot or cold outside?

5. I know you replaced the battery recently but, is your battery hold down bar on your battery? The reason I ask is because I see these X308's come in without the bar on them.

6. If you do have the hold down bar on the battery, make sure the that either or both of the hold down bar bolts are not overly tightened and bending the battery case. It's a long story but this one mans 00' XK8 spent $2500 at the Jag dealer to fix a problem (which they didn't) and it turned out to be the battery was over tightened.

7. Behind the battery are those (2) 250 amp power fuses that your + cable secures to. Are all those connections clean and tight?

Many times I've overlooked the basics when I'm in deep with an electrical issue so these questions may or may not be of help. But I'm not there to see the car either.

 

A2B: Not sure what you meant by "not sure where you live:" possibly not aware of the super wet and cold weather in Gig Harbor Washington.

You are right, weather matters: might put your address in your data, too!

 

I'm on my iPhone 4S vs my laptop that I only occasionally use. Anyways, on the phone it doesn't show me specs like what car(s) are in the signature or where you're from under the persons screen name. Thanks for pointing that out, I'll try and fix that this weekend.

 

I think I found the problem. I went out to get my dog and noticed the parking lights were on. Checked the headlight switch and it was on auto. I turned it to off and the parking lights went out. Turned it back to auto and BLAM the car filled up with darkness. I replaced the head light auto relay and could not duplicate the problem. We will see what happens over the next few days. I live about 20 miles south of (Sunny when it is not raining) Bremerton, Wa

 

The fact is that the description of what is happening defies the known laws of electrical engineering. Therefore, there is either a measurement error, misunderstood description, a "standard case" of discharged battery, or Gremlins.

You cannot have a good, CHARGED car battery post voltage drop to 5.6 volts steady state without current well in excess of 400 or 500 amps. If it is flowing that kind of current, the something is getting hot and it sure isn't a capacitor on a circuit board.

Since it sounds as if airtracker knows how to use the instruments, then I assume that when measuring the 5.6 volts, the battery is discharged (even though open circuit reads good) and then the car is started with jumpers or a charger. What does " make sure the battery is charged" in the original post mean? I read that to mean it was not discharged, but was chrecked. If the battery needed to be charged, then I assume we are dealing with parasitic discharge.

On my MY 99 XFR, the "off state" current starts at about 86 mA as I recall, then drops to 14mA after about ten minutes. Given the fact the security lamp seems to be acting up, I suspect that the security system is not going to quiescent state. That has been reported to sometimes be a result of the "linear switch" in the ignition lock hanging up. As you slide the key in or out of the ignition, there is apparently a switch to detect that and cause the transponder to read. If that circuit is holding on, excess current is drawn from the battery the entire time the car is shut doen.

Good luck. It is much easier to fix a circuit that exorcise deamons.

 

Ross;
Wrong assumtion on using instruments. I was using a digital multimeter, when I switched to an analog meter the voltage went to 14.1 disconected and connected. If I put a 1 meg resistor between the leads of the digital meter I get 14.1 connected and disconnected. Ohms law still works, if R is infinite I is zero and thus V is zero. The serial input impedance to the digital meter is 100meg to limit the effect of the meter on measurements, which is great untill you try to measure voltage across a device with no or very very low current flow. it has been 3 days now and so far it is still working correctly. I have poured over the Jaguar schematics and still haven't figured out why that relay caused the problem. I am speculating that the DPST relay had one set of contacts sticking which provided some kind of sneak circuit. My memory of random electrical gremlins was considered normal in my older British Leyland /Morris Garage vehicles. I assumed that switching to Bosch electrics fixed that. Thanks for your input on this problem.
Don

 

Take note of the sliding switch. It fires up the security system to read the key transponder. I think I recall others suggesting spraying the lock cylinder with contact cleaner, then lubricating it with graphite, but that seems a little risky to me.

 

The failed relay was not going to cause me loss of sleep. I performed a failure analysis on the failed relay (cut it open with hack saw), and found that the dpdt relay had one set of contacts that was only making on the energized contacts. When deenrgized they would stop in the middle. The contacts that failed provide power to the body module. I THINK maybe when I have learned all the Jaguar unique electrical symbology, I might be able to understand why this performed like it did. If and when I do I will share it with the forum.
Don