Starter relay location and test 93 xj40

Nearly all electrical functions incuding fuel and brak pumps but no engine cranking nor any starter solnoid clicking so need to locate starter relay to test??

Relay locations page 10,

http://www.jagrepair.com/images/AutoRepairPhotos/XJ6%20VDP%201993%201994%20Elec%20Guide.pdf

It may be the starter relay but a couple of other things will prevent a sound starter relay from energising.

I presume you are trying the starter with the transmission in ‘Park’ and your foot on the brake pedal? Try it with the gear selector in ‘Neutral’ in case the rotary transmission switch is not correctly set.

Similarly, have you checked that with the ignition ‘ON’ the brake (stop) lights illuminate when you depress the brake pedal? If not, the brake switch may be defective and that will prevent the CPU from allowing the starter relay to energise.

Yes even the dash brake light came came on as pedal depressed. Rechecked fuses as all were good. Dropped right side knee bolster and realized there were no individual relays only 3 or 4 long multi wired snap up assemblys yellow, red and two blues. Recall the yellow one inluded the “starter” but Haynes manuel left me clueless for collection of wires were specific. At tnis point I willjack it up safely secure it and attempt to verify power at starter solnoid unless you know one step easier? At my mid eightys is this reality to persist with such nonsenxse.?

Not according to my circuit diagrams. It is the 4th element of relay module ‘G’ (the one with the Blue base/connector) in that position which is the starter relay. It is energised when the the White/red wire from fuse #6 in the centre fuse box to pin 10 of the Blue relay connector goes to ground via the Green/orange wire from pin 19 of that connector. That Green/orange wire goes to the rotary transmission switch on the tranny and providing that switch is in the ‘P’ or ‘N’ position, the Red/orange wire from it to pin 47 on the Yellow connector at the CPU should go to ground if the ignition key is in the ‘start’ position III.
However, (there always is a ‘however’!), the CPU will not allow that circuit to go to ground unless the Brake Switch is ‘made’ indicating that you have your foot on the brake pedal.

BTW, I do not remember a “dash brake light” illuminating when I applied the brake on my car - only doing so if there was a brake fault. Does the stop light illuminate when you apply the brakes?

Hi Bryan, was the requirement to depress the brake before the starter would engage introduced from the first 93 model? I only ask in case there is a relevant difference in the schematics and it’s throwing you both off ? although my 94 MY sovereign had the ’ depress brake ’ feature my current 93 is not like that and will start without pressing the brake providing the lever is in park or neutral. I’m guessing/ hoping it’s been like that from new.

You don’t have to press the brake in my 94 either, car will start if in P or N

Casso, Larry - I stand corrected.

Perhaps I am getting confused with the starting procedure on my current wheels - a Range Rover - which does require foot on brake before starter will engage. I thought all automatics required that for safety reasons but obviously not the XJ40 although I thought my long departed '91 did! :slight_smile:

The circuit diagrams for a '93 certainly show the brake switch ‘in circuit’ with the CPU/starter/gearshift interlock wiring but I see know that could just be the requirement to press the brake pedal before the gearshift can be moved out of ‘Park’ without affecting the starter circuit.

Could the stuck gear shift in park position again be a suspect even if i have had this lockout in the past it was mechanically released by a slender chopstick and 2nd or 3rd time by a long slender screwdriver but was startable each time while locked as i recall. These were intermittently over months. This latest non start occurred after it set undriven for 2 months perhaps and once more has to be released and moved through all gear and neutral and no reponse by starter. Charged up battery and most everthing electrical functions as instruments, fuel pump, brake pump, horn, lights, except door entry lights. And it was always quick to start. There is clearly no starter solinoid click. And no brake light issue at instrument panel, turn signal works. I also looked up from below and spotted starter and tapped with a small hammer it few times with no results.

The Haynes manual shows something described as a ’ Security Switch ’ in the diagram for a 93/94 starting and charging system. I don’t know what that is myself but fairly certain Bryan will know, but could it be a safety cut out that trips and isolates the starter following an accident, and somehow yours has been activated and needs resetting ?

I too don’t know what that “Security Switch” does!

If Haynes means the ‘Inertia Switch’, then if that was tripped in an accident you would get nothing when you switched on the ignition - no panel lights or anything else.
There is a ‘Security Switch’ in the security system located in the centre console glove box and I see that affects the starter relay in the CPU so perhaps that inhibits it, so you may be on to something there.

Hi Bryan, Inertia Switch ! that was the one I was thinking of but couldn’t for the life of me remember what they were called when suggesting it. It makes sense it would isolate everything and not just disable the starter in event of accident too.
Regarding that security switch in the centre console, I just unearthed my handbook and it says in the ON position all functions of the security system will be armed, and the first on the list of those functions is ’ Starter Motor Disablement ’
In the OFF position the entire security system is switched off except for the central locking and window closing part, and if programmed by dealer the emergency closure button.
So Larry, Maybe it’s worth trying that switch in the off position if you haven’t already ? or even checking your security system to rule out it’s not disabling the starter.

Dear LaJagy

Hi, I also have a 93 XJ40 that occasionally will not operate the starter Relay under the dash. It has never been a problem the first start of the day, only after driving and sitting after warming up. Most days multiple stop/start operations are absolutely normal. Then the next day, maybe exactly same weather, same timing, I’ll drive to lunch from work, eat for 45 minutes, and the car won’t start, sometimes for 10 minutes, sometimes longer. I finally found through reading a Jag forum in UK how to manually start by turning the key to the Run position (II) and press the armature on the Starter Relay. No amount of wiggling the Gear Selector or jiggling the key helps. Resoldering the relay PCB hasn’t resolved the issue either. Did you finally come to a conclusion and resolution?
Thanks!