Hi , used the xj last night , yes of Course xx problems , came to start this morning and nothing will not crank .Battery is fine , dash fully illuminated etc , faint click under bonnet when key turned but thats it . Parking light is illuminated red so dont think its the gear lever inhibitor . Any suggestions greatfully appreciated

 

Could be the starter. Can you bang on the starter with a screwdriver or something? That could free it up

 

There is a inertia / crash switch that can be tripped and is always located on the right car side in front of the engine ECU . press the bulb

The picture is from a British right hand steering wheel model





The started solenoid relay ( above the engine ) must click to close and provide power to the starter / solenoid assembly as they are attached to each other

There is 2 fuses to this starter solenoid relay , this is different then the large battery cable power that passes through the starter solenoid itself on it's way to the starter motor

# 3 / 25 amp left engine fuse box , this fuse is hot at all times and does not need a relay to close

and # 12 / 10 amp right engine fuse box , this fuse is only powered when the right engine fuse box relay closes ( called the ignition positive relay )

And # 5 / 10 amp trunk fuse box for the Body Processor Module , hot at all times

The BPM is an important part of your starter enable

The # 1 fuse is closest to the large terminal post on the fuse box

The relay can click and still be defective in not properly conducting power to the starter solenoid ( the heavy battery cable current passes though the solenoid on the way to the starter motor )

You can swap this relay ( large left # 4 ) with one of the same part # like a headlight , fog , A/C clutch relay

The key is to have the relay click by placing your finger on it as other relays click at the same time and if not there are areas to look at

Your P light is one of them that you are showing

These relay can be stuck in their socket by a sealing O - ring and can be loosened with some penetrating spray

2 other relays to feel click while you are there as your ECU must be powered to enable the starter solenoid relay to click and those are the large ECU controlled relay ( right # 5 ) and the small ignition positive relay ( right # 9 ) you can swap this small relay with the one on the left engine fuse box ( in reality the left only runs the horn )

The ECU must be powered first for starter solenoid enable and after it rotates the engine the ECU does it's thing to regulate the engine in the normal way of thinking

 

The inertia switch disables the fuel pump. The engine will try to turn, but never will because there is no fuel.

If the engine isn’t even attempting to turn, it’s not the inertia switch.

 

The fuel pump relay relaxes to the open position in 2 ways with the inertia switch , the loss of ECU provided ground for the fuel pump relay control half and the interruption of control power sitting on the same control half of the fuel pump relay to close it

When the inertia switch no longer makes contact with the 2 white wires it will relax the right engine fuse box relay ( ignition positive relay , there are 2 ignition positive relays ) thereby umpowering the ECU by fuse # 12 of the right engine fuse box , this is the loss of ECU provided ground to the fuel pump relay control half to close the fuel pump relay

This can be seen as page 32 point 7 stop sign double hash . 38 as point 32 circle double hash , and 40 as point 7 stop sign double hash

The fuel pump relay losses it's control half power at point 6 circle ( this time ) double hash as this point is powered by fuse # 10 / 5 amp ( page 38 and 60 ) supplied power by the right heelboard fuse box relay ( also called a ignition positive relay as there are 2 on the car ) not being closed anymore and the consequent loss of power to the control half of the fuel pump relay

This accurse at the same time the inertial switch is tripped

 

Editing the above wording . I'm scrambled

 

Parker….I’m not nearly as qualified to speak to this as you are. I enjoy your posts and your thoughtful and helpful suggestions.

Can you do me a favor and trip your inertia switch and try to start the car? My 1996 XJS with the AJ16 engine will try to start, but will never turn over. Does your car stay silent?

 

I'm not so qualified as I have a dead Jag in the driveway

Starts now with the help of others but has some issues still pending ( ragged edges ) in the starting department

Not really confident on removing the inertia switch circuit if I can discern a different that can be accurately defined , but will give it a try and observe

Is yours rotating but not lighting off as there is a problem connector from the trunk to forward between the SLCU ( Door Lock Control Unit on your XLS on page 37 of your schematic ) to the BCM that is probably different on your XJS

Your engine regulation is on page 64 and there may be some inaccuracies in the schematic vs. what is really happening as they made the AJ16 engine work in your chassis

On quick check I don't see any identifiable inhibits on the left side of the engine ECU on the print other then the serial communications data link or the park neutral transmission


This is the schematic for the 96 XJS with the AJ16 engine although the link title is mislabeled

X300 1996 LWB.pdf (jagrepair.com)

This is the large 48 pin BT4 connector on the X300 chassis

 

No, do not remove it, just tap it to set it off. Then try to start the car. Do not go through the trouble of disconnecting.

 

I already ruined one while taking it apart and all the small spring loaded pieces flying everywhere and lost

Don't do this , or this will happen

Have a replacement one to install later as using a jumper between the 2 white wires simulating a untripped switch

I can mount the replacement switch as I will be doing it anyway

 

I think Vee is correct re the inertia switch, and in relation to the starter. The clicking noise is likely coming from the starter solenoid, which engages the starter pinion and connects power to the starter motor as the pinion meshes. It can stick, and a sharp tap can free it. It can also be caused by a weak battery or dirty connections too, where the solenoid isnt stuck, but just doesnt have enough power for the job. Your battery would have to be pretty low for that though.

 

Pulling together the variables ( including me) to make some more observations

I did only once have a definite solenoid chatter as had a definite low battery charge a couple of days ago

I do ensure the battery is fully charged but ..............you know things happen like losing track of the fuel condition ( water contamination ) even though aware of it

But the main thing is I can start it

 

I had the same problem and found that I had to replace the safety neutral switch on the transmission. ou can test it by locating the thin wire that comes of the starter and jumping it directly to the battery when the key is turned on. When I did this the car started so I knew I didn't have to replace the starter which is a real PITA. I have a 1995 X-300 in line 6 cylinder/

 

According to Jaguar, it disables ignition controlled circuits INCLUDING the fuel pump, which results in no crank. That said, the click from under the bonnet suggests to me that this isnt an inertia switch problem.
XJ6 Battery Change - Jaguar Forums - Jaguar Enthusiasts Forum

 

Not for the XJS then, I can attest that it will fool you into believing it’ll start, but the engine will never turn over. Good way to burn out the starter though! I guess on the x300s, they changed that.

Back to the problem at hand, I would follow piper888’s post above.