[xj40] P.I. Memory Battery Drain

Folks,

My son’s 93 XJ-40 (U.S. version) has been draining it’s
battery so rapidly that he carries a spare battery at all
times in his trunk. Today we did the hook up ammeter to
battery and pull all the fuses one-by-one routine, and found
that his typical battery drain is ~650 mA. The fuse that
cuts it down to about 70 mA (still a bit high, but much more
tolerable) is on the passenger side door panel fusebox,
column B (middle column) row 5. It’s a 10 Amp fuse that
supplies the P.I. (Petrol Injection?) memory. Does anyone
have any insight into why this battery drain is occurring,
and how to solve it?

Regards,
ABQ Jerry–
ABQ Jerry
Albuquerque/NM, United States
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In reply to a message from ABQ Jerry sent Sat 12 Feb 2011:

Jerry,

I’m a long way from my circuit diagrams at the moment but I
did an archive search on fuse B5 in the right side fuse box

  • the ECM (EMS ECU) memory power supply (which I suppose is
    the same as a ‘PI memory’) - and came up with this little gem.

[See the last four posts in this thread]

http://forums.jag-lovers.org/av.php?1372662l66

I can’t imagine why but Joe Adams appears to have found that
the problem of that fuse B5 blowing was due to a short in a
cigar lighter circuit (!).

Could your battery drain problem be in some way connected
with that accessory?

I’m sorry I can’t research this apparent anomaly by
scrutinising the circuit diagrams - but if you haven’t fixed
it by the time I get home in March, I will certainly have a
look! :-)–
The original message included these comments:

My son’s 93 XJ-40 (U.S. version) has been draining it’s
battery so rapidly that he carries a spare battery at all
times in his trunk. Today we did the hook up ammeter to
battery and pull all the fuses one-by-one routine, and found
that his typical battery drain is ~650 mA. The fuse that
cuts it down to about 70 mA (still a bit high, but much more
tolerable) is on the passenger side door panel fusebox,
column B (middle column) row 5. It’s a 10 Amp fuse that
supplies the P.I. (Petrol Injection?) memory. Does anyone


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Sun 13 Feb 2011:

Bryan,

It’s clear you are a better archive searcher than I am,
though I’m afraid that’s faint praise!

While 600 mA doesn’t sound like a dead short, I guess it’s
possible that a lighter has malfunctioned and is drawing
some current. We’ll certainly check it out.

Many thanks for your help.

Jerry–
The original message included these comments:

In reply to a message from ABQ Jerry sent Sat 12 Feb 2011:
Jerry,
I’m a long way from my circuit diagrams at the moment but I
did an archive search on fuse B5 in the right side fuse box

  • the ECM (EMS ECU) memory power supply (which I suppose is
    the same as a ‘PI memory’) - and came up with this little gem.
    [See the last four posts in this thread]
    http://forums.jag-lovers.org/av.php?1372662l66
    I can’t imagine why but Joe Adams appears to have found that
    the problem of that fuse B5 blowing was due to a short in a
    cigar lighter circuit (!).


ABQ Jerry
Albuquerque/NM, United States
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In reply to a message from ABQ Jerry sent Sun 13 Feb 2011:

70 mA isn’t far off the pace (my Jag draws 50 mA quiescent). But
the high figure is ceratinly wrong. It the PI the only thing on
that fuse?–
Alan (XJ40 3.6L 1987/8)
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In reply to a message from Alan4d sent Sun 13 Feb 2011:

Folks,

(esp. Alan) The 70 mA was measured on the 10 A full scale
range on my V-O-M, so it’s probably not terribly accurate;
the key issue is that it’s 10X what it should be.

My son tells me that there aren’t any cigarette lighters in
the sockets, nor does he have anything else plugged into
them, so that suggestion seems to be a dead end. I’ve
started trying to figure out the circuitry with the help of
the circuit diagrams in my CD-ROM, but haven’t found it very
useful just yet. The diagram for the cigar lighter circuit
doesn’t seem to be at all related to the ECM (Bryan’s
suggestion for what the PI memory may be). Perhaps a couple
of wire bundles that cross are fraying their insulation?

Anyone have any further suggestions?

Regards,
ABQ Jerry–
The original message included these comments:

In reply to a message from ABQ Jerry sent Sun 13 Feb 2011:
70 mA isn’t far off the pace (my Jag draws 50 mA quiescent). But
the high figure is ceratinly wrong. It the PI the only thing on
that fuse?
Alan (XJ40 3.6L 1987/8)


ABQ Jerry
Albuquerque/NM, United States
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In reply to a message from ABQ Jerry sent Mon 14 Feb 2011:

Jerry,

70 mA is not ten times what it should be.

To do any serious trouble shooting you really need some
‘readable’ circuit diagrams. The ones I use are included in
the JDHT CD-Rom JHM1130. If I currently had access to my
copies I could tell you everything that is served by that
right side fuse B5 in addition to the ECM memory function if
it is indeed that circuit which is causing the excessive
current drain of ~650mA you mentioned in your original post.
I will not be able to do that for the next couple of weeks
until I return to the UK but perhaps someone with a copy of
that JHM1130 will look it up for you.

I think that Joe Adams post relating to the cigar lighter
problem is probably a ‘red herring’. In any event, the cigar
lighters on my '91 car are not ‘live’ unless the ignition is
switched on.–
The original message included these comments:

(esp. Alan) The 70 mA was measured on the 10 A full scale
range on my V-O-M, so it’s probably not terribly accurate;
the key issue is that it’s 10X what it should be.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Tue 15 Feb 2011:

I have a CD labelled ‘‘JHM 1126’’, does anyone know if that is
the CD equivalent of the ‘‘JHM 1130’’ DVD?
I find the electrical diagrams exceedingly difficult to read,
and next to impossible to figure out where the fuse, relay,
connector, etc on the diagram is actually located in the car.
but then I never claimed to be proficient in automotive
electrical.–
The original message included these comments:

To do any serious trouble shooting you really need some
‘readable’ circuit diagrams. The ones I use are included in
the JDHT CD-Rom JHM1130. If I currently had access to my


84 XJS, 89 XJS, 89 XJ40
Santa Barbara, CA, United States
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In reply to a message from WayneC sent Tue 15 Feb 2011:

All,

As Bryan pointed out, the 70 mA reading is not 10X normal.
Of course, I meant the 650 mA figure noted in my original
post. Sorry, poor choice of phrasing.

In any case, I have JHM1153 (v1.1), not JHM1130, and haven’t
found it to be very useful relative to circuit diagrams.
I’ll keep looking.

By the way, we checked that the reading lights on the
backside of the front seats are indeed off, and that there
were no conductive objects in the cigar lighter sockets.

We’re still hoping for that AHA! moment… and appreciate
all your thoughts.

Regards,
ABQ Jerry–
The original message included these comments:

To do any serious trouble shooting you really need some
‘readable’ circuit diagrams. The ones I use are included in
the JDHT CD-Rom JHM1130. If I currently had access to my


ABQ Jerry
Albuquerque/NM, United States
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In reply to a message from WayneC sent Tue 15 Feb 2011:

JHM1126 is the orignal CD-Rom produced for the XJ40 - and it is
particularly difficult to navigate compared to the later JHM1153
but the wiring diagrams in both are very diffcuot to follow.
JHM1130 includes completely re-drawn circuit diagrams I believe by
JCNA for the US market because all are for LHD versions so
allowances have to be made for those of us with cars with the
steering wheel on he correct side!

I would strongly recmmend that anyone with a serious interest in
the wiring of their car should invest in a copy of JHM1130 - even I
can understand and follow those! :-)–
The original message included these comments:

I have a CD labelled ‘‘JHM 1126’’, does anyone know if that is
the CD equivalent of the ‘‘JHM 1130’’ DVD?
I find the electrical diagrams exceedingly difficult to read,
and next to impossible to figure out where the fuse, relay,
connector, etc on the diagram is actually located in the car.
but then I never claimed to be proficient in automotive
electrical.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Wed 16 Feb 2011:

Thanks for the reply, Bryan…
Any chance you could email me copies of a couple of the
‘‘improved’’ electrical diagrams you like, so that I can
compare them to my JHM 1126 to determine if spending another
$50 is a good use of my money?–
84 XJS, 89 XJS, 89 XJ40
Santa Barbara, CA, United States
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While we’re on the subject, is it still the case that these CDs can only be used on a Windows machine, and it can’t be any more recent than XP?

A few years ago I bought the disc for my series III V12 and got completely fed up with it. First, I was hacked off to discover that even though the content was a bunch of pdf files I could only access them through the included program - so I couldn’t load the disc on any of my Macs. Then I discovered it didn’t work properly with Vista, the operating system on the only PC I had access to.

JustinOn 16 Feb 2011, at 19:36, Bryan N wrote:

JHM1126 is the orignal CD-Rom produced for the XJ40 - and it is
particularly difficult to navigate compared to the later JHM1153
but the wiring diagrams in both are very diffcuot to follow.
JHM1130 includes completely re-drawn circuit diagrams I believe by
JCNA for the US market because all are for LHD versions so
allowances have to be made for those of us with cars with the
steering wheel on he correct side!


Justin Hill, Surrey UK
Jaguar XJR 07/1993 “Roger”
Volvo 850 20-valve 1995 “Victor” the freebie
jhill@cka-net .com

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In reply to a message from WayneC sent Wed 16 Feb 2011:

Don’t believe I can do that.

Take my word for it - they are 1000% better than the factory
Service Manual version–
The original message included these comments:

Any chance you could email me copies of a couple of the
‘‘improved’’ electrical diagrams you like, so that I can
compare them to my JHM 1126 to determine if spending another
$50 is a good use of my money?


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Justin Hill sent Wed 16 Feb 2011:

Justin,

Mine operates on Vista - but I belive mine were early pre-
production copies (or something) and I’m not computer savvy enough
to undrstand why mine work OK and others do not.–
The original message included these comments:

While we’re on the subject, is it still the case that these CDs can only be used on a Windows machine, and it can’t be any more recent than XP?


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Thu 17 Feb 2011:

Folks,

I read my CD-ROM with a Mac (system 10.4.11) using Preview
to read the individual jpg files. Not as convenient as
using the built in app, but it still works.

After having pondered the circuit diagrams, it appears that
fuse B5 (right side) feeds the fuel injection control
module, labeled item 144, aka the PCMF, and nothing else.
(Incidentally, there’s an error on the diagram suggesting
that it feeds item 142, but careful examination of the
actual wire info shows this not to be the case.) The PCMF,
in turn, powers the fuel injectors and also links to the
idle speed control/idle switch.

Does anyone have any suggestions how either of these could
result in the observed drain? If not, I’m going to have to
revert to my chafed insulation theory and start pulling on
wires/cables.

(JP, having replaced them, I know that this car doesn’t have
door handle heaters. Thanks for the help, though!)

Regards,
ABQ Jerry–
ABQ Jerry
Albuquerque/NM, United States
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Hey there, been reading this forum a lot and decided to finally start discussion.

My XJ40 has massive baterry drain and with a help of multimeter I have found that there a 3 fuses who are responsible for it:
A1 - lh front seat motors & heaters
B1 - rh front seat motors & heaters
A3 - speed warning. Facia switch pack, ign on relay, p.i. memory

The biggest drain is for A3 fuse. The problem is that if I remove it, I can’t start the car because it is responsible for ignition.
So is it possible just to remove/fix P. I. memory thing because I read that it mostly the cause of battery drain?

Try leaving fuse A3 in and remove the ignition on relay. Does that stop the drain? If so, try swapping the relay with a known good or new one of the same type.

1 Like

Thanks for the idea - I’ve tried that but doesn’t help.

Now I am taking out the A3 fuse everytime I come back home, that is the only way to stop the battery drain.

Suppose I need to get somewhere deeper, but where?

By the way, tried taking out Auto Speed and P. I. Main relays as well - still the same battery drain. So what’s left?

I have 1989 XJ40 when first purchased used no mods on car and base mA drain was 33 mA probably just the dash digital clock.
When I added the auto start feature to car we are now up to50-60 mA

70mA for base level no add ons sounds high unless you have and alarm or added autostart added to car