Hi,My battery goes flat if I leave the car for 3 days.Took it to local jag dealer,who had it for a week and found nothing but still charged me for the pleasure of opening the boot.i have put a new battery and had the alternator tested which was ok.
I have tried leaving the vehicle unlocked incase it was a central locking/ alarm fault but fault still occurs.
I took it to an independent specialist who carried out a diagnostic test .
Faults Found were listed under rear electronic control module namely sliding roof short to earth and r/h & l/h rear tail light faults.
I find this strange as my car has not got a sliding roof and both rear lights are working and no fault was showing on dash display.
The faults were erased but returned after a short period.
Should I renew the rear control module & does anybody no wher it is located ?.
All suggestions welcome......I really don't want to part with the car but I am starting loose all faith in the beauty

 

Well lots of harnesses on the car are common without regard to option presence.

Now, if the harness for the sunroof is not used, but it is dangling somewhere and a lead is grounded then the diagnostic code might well be correct and pointed exactly at the problem. If it is on a fuse you might try the simple remedy of pulling the fuse as a first effort.

In addition, if it *is* the fault, then how come the dealer did not find it on their diagnostic system which every dealer is required to have as a term of their franchise.

 

Electrical draws are very hard to trace. I would go by the codes, and pull the fuses to the systems that are indicated by the codes and the ones not essential to the car operation. If this doesn't reveal the problem, I would pull the ones that are essential. If your car "goes dead after three days", you are not using it daily, so pulling some fuses in those three days, will not rob you of the car usage anyway.

This would be a long drawn and painstaking process, but with a lot of patience, you might be able to deermine which system is having the draw. If everything fails,......I'd go "old school" on it. I would install the switch (toggle) at the battery, and flip it every time the car is to be parked for more than a day. I would connect the switch to the positive at the battery, and place the switch itself in the convenient location.

Sure it would be inconvenient,.....all memory, radio, would be erased every time. There is another "old school" way though,.....connecting a solar battery maintainer. You could place the solar cells on the parcel shelf (velcro it in place), and connect the leads directly to the battery. The thing would continuously charge the battery, and counter the draw.

Of course, the best thing is to find the draw, and fix it, but there is no need to ditch the car because it's cost prohibitive to pay someone to look for it.

It just occured to me,.....you didn't say how old is the battery? Take it out, and leave it on the bench for few days, maybe it's the battery itself that doesn't hold the charge?

 

In his opening message he says the battery is new. Might still be a problem, but unlikely.

 

Yeah,....I missed that. So it's a new battery. Start isolating the systems by pulling fuses.

 

The way to find parasitic curent draw is to open the trunk, remove the trunk light bulb, install an ammmeter in series with the battery lead (either one) . Ater the car is shut down for a few minutes, the current should drop to about 50 mA. If it is higher, then start pulling fuses until you find the circuit with the current draw.

If there is no parasitic current, then you have a battery or charging problem and need to diagnose that instead.

It really is not very complicated, but people seem to spend an inordinate amount of time installing switches, solar chargers, new batteries and on and on chasing this problem.

 

Thankyou for all your input,I will try all when I have spare time.i have borrowed another car in the meantime,not quite an xj but it seems reliable !.
Keep you informed ...

 

The Jag battery has a capacity of around 90Ah, so for it to go flat in 3 days-which is 72 hours-the current draw must be in the region of 1 Amp or so. This is typically the current draw of interior bulbs such as glovebox, boot etc-which you can't tell if they have switched off as you can't see inside the closed glovebox or boot.

As Sparkenzap says, the only really effective way to find the excess current draw is to place an ammeter in series with one of the battery main leads-usually the earth lead as this is safest when avoiding accidental shorts & sparks etc.

Wait a couple of minutes for the car systems to shut down, then pull the fuses out, one-by-one, until the excess current draw falls.

It just takes a bit of time & patience-the fault could actually be very simple, so it's shame to consider junking the car for a small electrical glitch.

One of the main causes of electrical anomalies is when the original wiring has been altered or bodged when aftermarket installers start fitting stereos, alarms, towbar wiring etc. I've had more electrical faults due to aftermarket wiring bodging than by the original untouched electrical systems.

Quite often, removing stereos & trim panels can reveal various electrical horrors, with all manner of tape, dodgy cheap connectors & wires all bundled up & shoved anywhere where they can't be seen-hiding all sorts of troubles.

 

The other main source of parasitic load is the key switch contact that detects key insertion in order to fire the transponder. Once you have the ammmeter connected, try jiggling the ignition key in and out, looking for a current change.

 

Most people don't think of the stupid solution... but maybe it will be useful.
Check out the vanity lights on the sunvisor, and check that both of the glovebox
hinges are sealing properly. These are the 2 things in an XJ that can run
permanently without being noticed.

 

it is easy to check if boot/trunk light or glovebox light is staying on, set your mobile to video and shut it in. take it out, play back, you have you answer. just make sure the lense is not facing down.

 

andrew- I guess that is better than climbing in and closing the lid, huh?

 

Ive spent all afternoon carrying out tests as suggested.i connected digital ammeter between bat - terminal & earth . This read about 3.9 amps when I locked vehicle reducing to a slightly fluctuating .71 amps after a couple of minutes and remained at this..I then removed fuses from all fuse boxes checking for any reduction but didn't find any.
Is the .71 amp drain excessive,should the battery be able to cope with that amount.
When engine running battery reads 13.8 volts.
I checked the visor lights,glove box & boot lights as suggested ,no fault found there either.
Where should I look now.???

 

A current drain of around 0.71 amps is excessive & explains the battery going flat after 3 days. With the vehicle locked & all main electrical systems shut down, the current draw should be less than 0.1 amps & somewhere around 0.05 amps.

There are 5 fuse boxes on the car-2 under the bonnet, 1 in the boot & 1 each behind the rear heelboards.

If you look in the boot behind the battery, you'll see the main High Power Protection Module which is basically 2 very high current internal fuses. There are 3 terminals on this module:

1) The main thick red wire coming directly from the battery positive terminal

2) Another thick red wire which comes out of this module, goes to the front of the car & connects directly to the alternator main output & starter motor supply. This is fused at 500 amps!

3) The 3rd terminal has 2 wires coming out of it & these take the fused 12v supply to the 5 vehicle fuse boxes & therefore to every other electrical circuit on the car. This is fused at 250 amps.

Firstly, remove the single output wire from the stud which feeds the alternator & starter motor. If this makes no difference, then you know the fault must be in the supply from the stud with the 2 big red wires on which supplies all 5 vehicle fuse boxes.


You need to isolate each feed step-by-step until you locate the fuse box area which is causing the current draw. The boot fuse box is connected directly to the High Power Protection Module by a single supply wire going to the 3rd stud as in 3) above. So with the ammeter in place, remove this supply to the boot fuse box & see if the current draw falls way below 0.71 amps. If it does, then you know the fault will be in the boot fuse box.

If this has no effect, then you need to remove the other wire on the 3rd terminal as in 3). This wire supplies power to the other 4 fuse boxes in the following order:

1) RH Heelboard fuse box

2) LH Heelboard fuse box

3) Engine Management fuse box (the small one under the bonnet)

4) Engine Compartment fuse box (the big one under the bonnet)


If the current falls when you remove this main supply wire to the 4 other fuse boxes, then you can narrow the fault area down to here. The next step would be to remove the supply from each fuse box input separately, by disconnecting the thick red supply wires at the main studs on the fuse boxes-depending on accessability, which could be a problem. You'd need to work backwards-starting at the under-bonnet fuse boxes & ending at the heelboard fuse boxes until you pin down the culprit.

If all this fails, then the only other thing is any aftermarket devices installed which may have their own connectors bolted directly to the battery positive terminal. These can usually be spotted as they generally don't look tidy or professional & the wires may not be crimped on the terminals properly.

With faults like this, it can take a long time & a lot of detective work to isolate the fault-but stay persistent, as it has to be in there somewhere!

 

Red October is spot on, but I would add that you just about have to have missed a fuse. If you did not and have to follow his procedure, be very careful to not let any of the power leads get to ground!

 

Ok thanks ,I wasn't aware that there were 5 fuse boxes,according to the handbook there are 3,one in boot,bonnet & drivers side heel board . These are the fuses that I removed which didn't make a difference to tha drain.
Is the main fusebox protection module mounted on the inside of the rear panel (number plate). This has several large cables to and from it and the covers are secured with cable ties.

 

Yes, there are definately 5 fuse boxes-2 under the bonnet, 1 in the boot & 1 each behind the rear LH & RH Heelboards. I've done a lot of wiring work on my car recently so I can vouch that all 5 fuse boxes are indeed there

The handbook may only be mentioning the fuseboxes for 'popular' fuses that may be expected to fail, such as headlights etc. The other fuseboxes contain more system-specific fuses that are more relevant to Main Dealer servicing etc.

The main fusebox protection module is mounted in front of the battery to the left-as viewed from the rear of the car looking forward. It's at the parcel shelf end of the battery-not the number plate end. You can't miss it-it's got the main thick red positive cable going into it directly from the battery positive terminal. It sits just in front of the spare wheel, so you'll get a better view & access by just pulling up the boot floor carpetted panel/spare wheel cover.

Oh yes-as Sparkenzap says-do not let any loose power leads dangle to earth, as you will indeed get a spark & zap, followed by a fresh set of underwear

 

Back to the jag,bin on it all morn and pulling my hair out,not much left now !!.
I can still only find 3 fuse boxes.i had all footwell trim off which revealed an front ecu module and a fuel shut off.Under bonnet fuse box on left as you look from front.
Anyhow back to tests as you suggested .The power protection is bolted on the inside of rear panel number plate end.
Ammeter in place.tests carried out.
No difference on removal of alternator/starter motor cable.
Slight difference of .3amp on removal of one of the cables(mega fuse 175amp)
No drain at all if I disconnect both cables (175 amp) and top cable (100amp) so I thought this is the problem.would I be right to assume that this is the supply to the fuse box in drivers footwell only.
I then disconnected the supply to this fuse box at two terminals , one with one cable and another with two which I think goes to the bonnet fuse box.
The ammeter was now still showing .5amp.
I then had to call it a day as no more time...
What next....???

 

At this point I would connect a solar charger, or a trickle charger/maintainer every time the car is parked for more than overnight, and go do something with my life.

My bikes are all on trickle charger, because I don't ride them enough. It's no problem to park the vehicle, open the trunk, and have a quick connect plug in there to plug the lead from the charger (on the bikes the plug is protruding slightly from under the seat, and the chargers are on the shelf with the cable hanging against the wall).

To each his own,....I just don't have enough patience (or time) to chase something like this, and I would certainly not get rid of the car I like, if a problem like this presents itself.

 

I no what you mean,beginning to feel its time to change to a mondeo .lol