I had to jump start my mothers 97 due to a dead battery. After charging up the battery it was dead again after a day or so of sitting.

Testing the system it's drawing .5 amps with everything off (doors locked, trunk jimmied so it thinks its closed etc..).

I went searching for the current "leak" and found F5 in the drivers side facia fuse box drawing .3 amps with everything off.

There appear to be 5 fuese in this car labelled "BPM" - does anyone know what F5 is powering? What am I going to be disabling by pulling it?

I still need to find the other .2 amps (passenger side and engine fuse boxes to go).


I also jump started the car using the post in the fuse box on the passenger side. I read in a thread this is a big no-no, I'm wondering why?
Trying to jump from the battery was not working, I've run across this with other cars. If the battery is really dead, it will suck most of the juice and not pass much on to the starter. I'm surprised Jaguar didn't install a dedicated jump start terminal under the hood that goes directly to the starter. If I ever buy one of these for myself, I'll be adding one.

 

According to what I see, "BPM" is the Body Processor Module" and F5 is the fuse feeding the "logic" portion of the module. It sounds as though the module is not shutting down when the car is off.

Could be a bad module, or some inputs to the module keeping it "awake." Looking at the wiring diagrams, the BPM is involved with quite a lot, almost every interface betweent he driver and the car.

Any stuck switches, or anything else that isn't working right? tilt telescoping wheel? key in ignition warning? shifter not in park warning? memory seats? heated seats? trunk and fuel door release? Convertible top? Horns? keyfob remote fuinctions?

 

A few questions........

How long are you waiting to take a current measurement after closing up the car? You say "jimmy the trunk so it knows it's closed", how are you doing that? Closing the latch is how the thing knows it's closed. The big "button" on the lid is only an assist spring to disengage the latch. Are you using some sort of disconnect device, so the car can properly power down with battery power, and go to sleep before opening the connection and allowing an ammeter to measure the quescent current? It can take 45-60 minutes for the electrical system to power down to the final current draw, which should be around 30-40 mA.

Also note that pulling a fuse or opening a latch wakes the system up and means another waiting period for it to go to sleep again.

Good luck!

 

It's a convertible, sorry, forgot to mention that.

I'm shoving my finger down the latch until it clicks and the trunk lights go out. I was hoping that big button didn't have to be held in too, wasn't sure how I would go about doing that.

I also left the drivers door open, manually closed that latch turning off the interior lights, then I locked the car.

I waited about 30 minutes before checking the fuses individually. By the time I reached the F5 fuse mentioned above, it was about 15 minutes later.

I checked the trunk fuses first, all were zero amps. Every other fuse in the drivers side box were zero except the F5. Even the other BPM fuse was zero.

The fuse for the instrument cluster would draw 2 amps once re-connected and I could hear some mechanical noises before it settled back to zero.

I didn't check the airbag fuse due to that safety clip. I know why it's there, just nervous about ever getting involved with air bag systems.

I'll report back after testing the passenger side and engine compartment fuses.

 

the spec is less than 30 milliamps after 30 minutes give or take

 

Is that 30 minutes after the engine is off or 30 minutes after no activity from any device?

 

30 mins after input from any device.

Also be aware that pulling fuses can reset the countdown time. I have successfully used a clamp on ammeter to measute the current flow in each circuit after replacing each fuse in the suspected fuse box with a wire extension loop to enable measurement. Current flow in each circuit was then made after the required sleep time.

What is the current draw on the whole car after allowing it to "sleep"?

 

Here you go, let's make it official..........awful lot of opinions out there.

Hacker, you have an XK8 (X100)


Cheers,

 

Wow, thanks Steve!

To answer my original question - the F5 fuse feeds the parking lock activated by the brake. So if you pull that fuse, there is no shifting out of park. I'm sure it controls other things too.


Back to the no start problem, it appears I sent myself on a wild goose chase.

I figured it could be a bad battery, so I pulled a good battery off my work bench (that was on a maintainer) and installed in the Jag. It's a "normal" size battery, since the hold down plate had a 2nd hole drilled for a smaller battery I figured it would be fine for testing.

The next morning the car would not start....WTF? Meanwhile the battery from the Jag was on my maintainer. I pulled out my second maintainer, connected it to the battery in the car. If you have a maintainer, you know it can take a day or two to fully charge a dead battery. I waiting until the battery was full and started the current drain test, then started this thread. Once again, one night off the charger the car was dead…..back on the charger.

I waited until both batteries were fully charged, took them into a battery place for testing. Well stupid me, never thought to check the voltage of either one. Both were under 12 volts (original from the car was under 10).

I pulled the battery from my 928, which is smaller yet from my test battery, car fired right up. I let it sit overnight, started right up this morning.

So.....don't forget the basics.


I’m now wondering if the dying battery has anything to do with the intermittent top operation. Once and a while the quarter windows wouldn’t go up. Once the new battery is installed, I get to play with that.

 

I think there is a good likelihood the low battery condition was causing those other problems as well. Battery level is critical on any multiplexed car, modules can't think straight without full battery power.

Good luck.

 

The F5 fuse provides the Body Processor Module (BPM) with constant battery power for the Logic circuits. You are correct, BPM controls the shift interlock as well as many other items. In fact it shows up in 19 wiring diagram pages.

Glad you sorted your problem.

 

That was a nice read

Any chance of posting the whole thing?

 

I knew I'd posted the stuff before.......I had to hunt it down.

Here is the whole thing in an earlier thread; actually, the whole thread is a good read.

https://www.jaguarforums.com/forum/2...29/#post337329

Edit: plumbsauce, you seem to like details, huh?? I think you've done that to me before.

Cheers,

 

Thanks muchly.

You know what they say, "the devil's in the details" and "knowledge is power".You never know when some little detail is going to trigger the "AHA!" moment while puzzling something out.

BTW, if the transponder key is close by, does it keep the system from going to sleep? That's always been a puzzling point when the current draw threads come up. If it does, it would defeat the purpose of the test if someone is walking around with the key in their pocket. Someone, somewhere, suggested that approaching the car with a transponder wakes the systems up in preparation for starting. The additional implication is that leaving a spare key in the car at all times would keep the system from ever going to sleep.

Here is a minor bit of information regarding battery vents, less the rant part:

https://www.jaguarforums.com/forum/j...venting-55908/

 

Ok, the OP has a 1997 XK8, that car has no transponder key, doesn't apply to him, the transponders were introduced in 1998. The business about the key being close by and keeping it awake doesn't apply until the "Smart Key" introduced with the 2007 XK, and continuing with the XF and the new XJ in 2011. All the cars in between only "wake up" when the key or remote unlocks the doors; that's the signal, "hey, we're about to go somewhere".

Hope that helps.

 

... and does the tail wag then?

Seriously, thank you for clearing that up.