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Hi All,

Over the weekend I was tapped-up by my neighbour who had recently purchased a 2 owner 1996 X300 4.0 AJ16 Sovereign with 78K on the clock with a full Jag service history. Evil chrome wheel arch trims aside and some very odd paint damage to the boot lid, the car is in excellent condition. Unfortunately, it has refused to start since last weekend and we're both stumped as to what can be at issue. The starter motor refuses to actuate on key position 3 - no clicking - nothing. All lights/fuel pump priming/Abs charging seems to be taking place when the key is moved to position 2. Moving to position 3 does nothing. The car had a new crank position sensor and mass air flow sensor fitted last month in an attempt to address uneven idling that seemed to work. The car had been running for a few weeks with these both in place.

Its been a while since I owned my X300 ('96 Daimler Six) and comparing the '96 Sovereign with my 1994 XJ40 there are significant differences. Anyway, below is a list of investigative threads that have / are being folllowed. If anyone has any further insight / hints / tips / advice - all would be gratefully received.

Ta, Rich

1. Check battery - replaced with new one (640cc - not my choice) as old one had low voltage
2. Check starter motor - managed to get the starter motor actuating by shorting the wiring (I've done this before on my XJ-S V12 when I had a bad earth) so we know that the starter motor is good
3. Check all relevant fuses in engine bay, left and right rear bench locations and boot - nothing blown
4. Security system - both fobs are paired to the car and the central locking and alarming / dis-alarming is working fine
5. Gear box selector - happily moves between the different positions and will beep if engaged in Reverse and the ignition is switched to position 2
6. Dampness - all dry under the bonnet and we even had a hair dryer under there just for good measure

Other thoughts:
1. Logged error codes - we don't have anything to read these. A RAC chap tried reading and could not find any logged codes. He seemed to think that there was a fuelling issue at play. I'm not sure how that relates to a non-actuating starter motor
2. Gearbox micro switch - would such a switch prevent a starter motor from actuating? I don't know...
3. Isolation switch - I vaguely recall some sort of switch that triggers and isolates electrics and fuel if the vehicle is involved in a violent car crash - not sure how this could cause an issue when the vehicle has been standing for just a week

is there still a fusebox under the center armrest in these ?

if so , I had the same issue, a 2a fuse blew , car refused to start without this little fuse being replace

just a thought

BB

Thanks Vince - I will check this....

ok, an easy check on a 300. Ignition ON, all dash lights should come on a full set both sides

do not attempt a start, but wait for the lights to go out. They should all extinguish EXCEPT the check engine light, this should remain ON

some cars the transmission light will remain on, ignore this

The check engine light ON is a tell tale the ECU is awake and will send a signal to crank, and hopefully then fire

If the check engine light goes OUT, the ECU is still asleep and you will have no permission to crank, sound familiar

Have a check in the morning and report back

Thanks Rob. The transmission and engine management lights are remaining on so that's good news right?

Steve and I were chatting yesterday evening and the main area of suspicion is back on the gearbox micro switch. There is no "click" when depressing the brake pedal when the key is in position 2 with the gear shift in position Park so I'm hoping that we might be able to fiddle with that at the weekend.

Cheers, Rich

On is good!!, the fact it will not crank now points to ignition switch itself imo, OR possibly the intertia switch

have you tried starting it in neutral??

Linear switch possibly (on the side of the J gate)?

Hello Everyone,

As an update;
Over the weekend we were able to access the J-gate and persuade the micro-switch to work. Now there is a distinct "click" when depressing the brake pedal with the ignition switched to position 2. However, moving to position 3 we're still not getting any cranking (b&tch!) either in the P position or Neutral. Presumably that now leaves the inertia and the ignition barrel itself as suspects. Naki - for the less enlightened (me especially!) could you elaborate on what the linear switch does - is that something additional that is located deeper into the J-gate area that we've not spotted yet? Workload / family permitting we hope to take another look this evening as its just stopped raining.

Thanks, Rich

In other news - I changed the oil and filter plus the air filter on my XJ40 yesterday. Whilst shuffling around underneath I was extremely impressed on just how rot-free the underside is - the subframes and spring cups are in excellent condition. Sadly my optimism was short-lived as I spotted a suspect area on the off-side inner wing adjacent to the windscreen wash container. A bit of prodding with my screwdriver revealed the wheel arch lining and some daylight (d&mn... more work!) - hey ho!

Morning All,

After finishing work I was able to take another look at the car (X300 not the XJ40 for the avoidence of any confusion).

There remains a reassuring "click" when depressing the brake pedal in ignition position 2. Again, trying to start in Park or Neutral; there is still no actuation of the starter motor. In fact, all the lights on dash go out when moving to ignition position 3. I have taken some pictures to add some context to my waffle. If anyone get a chance to step through and review - I'd be grateful!

Ta, Rich

1. Ignition position 2 - lights on 2. J-gate area - anything else to check around here? 3. Drivers foot-well right hand side; where is the inertia switch? Mmm - looks like I'm capped at 3 images despite resizing and cropping the orginal pics - hopefully the above is sufficient.

Rich

wen I got to this stage on my ' late-40 ' I decided to see if I could crank the engine

this was by accessing the relay module behind the glove box, with ' starter ' written on the circuit ,

now I had to remove said relay box ( blue one I think in my case ) and take the cover off it, then with the module placed back in the plug ( less the cover ) I manually depressed the relay that makes the starter turn over, this worked perfectly , I had effectively bypassed the electrical control circuit for this relay

just something to look at that's all

BB

Thanks Vince. The starter motor is known to be good (i.e. the RAC chap was able to get it cranking over) but even when it was cranked in with the ignition switched to position 2 - she did not start at all.

I did not mention this earlier - but there is tissue paper (!!!!) located just above the "GEMS 6 Control Unit". This makes me think that some water ingress may have induced this error.

Any heads-up on what the GEMS 6 Control Unit is responsible for?

Ta, Rich

Rich,

See that grey rectangular electrical connector just to the left of the module?
Well the inertia switch is the black 'lump' behind it.
The 'reset button' is on the top of it.
Press it down, release, then see if it fires up when you turn the ignition key.

Steve.

Thanks Vince. The starter motor is known to be good (i.e. the RAC chap was able to get it cranking over) but even when it was cranked in with the ignition switched to position 2 - she did not start at all.

I did not mention this earlier - but there is tissue paper (!!!!) located just above the "GEMS 6 Control Unit". This makes me think that some water ingress may have induced this error.

Any heads-up on what the GEMS 6 Control Unit is responsible for?

Ta, Rich

Hi Rich - I think that GEMS stands for General Engine Management System which would suggest that box is your main engine ECU?

Hi All,

Thanks for the updates - I have not yet had a chance to look at resetting the inertia switch as last weekend it was my birthday, mothers day and "get those gold wheels back on the XJ-S for summer use" day

Hopefully this weekend will get some time.

Rich

Hi All,

Quick update - we have eliminated the inertia switch by shorting the plug. I think that we could be looking at an ECU issue as I have re-checked the dashboard lights and the engine management light is NOT staying on any more. All lights are extinguishing after 3 secs on ignition position 2.

How interchangeable are the GEMS 6 units? They have a body number associated with then so was wondering if they are paired explicitly with the car or just plug and play?


Thanks, Rich