In the past,,,, I did, and did, and did and did - many times... All of that was coming back to me as I tinkered today. I replaced the relay plug entirely back then, swapped relays (even though I knew the ones I was using were good). Eliminated (bypassed) long stretches of the green wire (wiring it closer to the connector plug on top of the bell housing) in case wire was damaged internally etc... Relay NEVER triggered relay (wired normally) except rarely rarely rarely - becoming rarer and rarer as time went on...

Today I did run the G and O wires thru an OEM brown relay,,, the only kind I've ever used,,, with no change... 11.25v on both sides of relay,,, no relay engagement with key turn. Tried experiment with car in D and in N. With the brake pedal engaged and not engaged... Still, no relay click/engagement.

Is it possible the problem could be in the "not in neutral switch" or the ignition dial on the steering column itself?

I also want to try from the other side as suggested earlier in the thread. I'm just not in a place where I can get that deeply into the dashboard today - if that's where these plugs can be located...

 

If you measure across the relay coil (should be 0 volts with the relay in place) and that doesn't change to ~B+ when you try to crank, then do indeed go to the other end and check the ignition switch is grounding the green/orange wire.

Probably best to try to tap in at the BPM end - that way you'd catch any break in the wire to the switch.

 

I'm sorry guys. I just don't understand... Please help me understand, in the most basic way, what voltages/readings one would see on a relay that is controlled by switching it to ground.

​​​I thought that if a relay was triggered (controlled) by switching it to ground (by ECM or other device - say a sprung toggle switch or something) momentarily,,, one would see 12v (or what ever the voltage is that's being supplied at pin 1 on the relay) on BOTH sides of the relay (pin 2 as well) UNTIL the ground side was switched...? Maybe even after and during the switch to ground one would see 12v or a fluctuating version of 12v?

It's interesting in the electrical diagram that the description is of the ORANGE wire being an OUTPUT. And green being an INPUT at the ECM, at least.

I think I need to dive in and chase the OG wire as y'all have said.

 

Yes, that's correct.

Again correct. The orange wire is an output from the ECM to the starter relay. It's normally 'floating' (effectively not connected). When the ECM wants to fire the relay, it will output a ground on the orange wire.

The green wire is an output from the TCM, which should be at or near B+ when the transmission is in Park or Neutral. That is what supplies power to the starter relay. It is also an input to the ECM so the latter knows the 'in park or neutral' state of the transmission.

If you're seeing 0V across the relay coil both at rest and when you try to crank then, providing there is B+ on the green wire (pin 1 of the relay, measured against ground), the ECM isn't commanding the starter relay to fire.

Hope that makes sense!

 

It does. Thank you Michael...
Now to figure out WHY the ECM isn't sending the ground signal to trigger the relay...?

I think it important to note that it DID, intermittently, at one point early on in this saga...then less and less and less.

Another thing I noticed today is that the entire instrument cluster died at the point where the key is turned to START. All gauges drop, all lights go off, everything.

Maybe it's a problem at the switch in the steering column,,, that not in Park Switch - or who knows...?

 

Do not make this more complicated than necessary :-)
In simpel terms;
1: Ignition switch is grounded (marked with a circle)
2: When you turn the ignition switch to start position, you got a ground signal to the BCM at FC14-41
3. If the BCM says OK, it sends the grounded signal from FC14-72 to the ECM at EM80-6 (Engine start request)
4. If ECM also think it is OK to start, it sends the grounded signal from EM80-41 (Engine crank) to the starter relay (Orange wire)

To check this, you got to locate the BCM, connect the one lead of your voltmeter to a known +12V (not ground!) an the other lead to pin 41 at the BCM. Turn key to start. If you get 12V then your ignition switch is OK.
Move the lead on your voltmeter to pin 72 at the BCM and turn key to start again. If you got 12V the BCM is OK and the problem lays at the ECM. If you do not get 12V the problem lays in the BCM.

Edit: I call it BCM - Body control module, but Jaguar calls it Body Processor Module aka BPM. Please dont let that confuse you :-)

 

NORXKR...you are causing confusion here ...the ignition switch does not switch an earth signal ..you have misread the symbol you have in green it is not an earth symbol. If you look directly above you will see an earth symbol on the battery.. The ignition switches 12v as required by the key position.

Jay Jay Jay.
If you had done what it says in post 16 /listened to michealh you would have it sorted by now.
Your dash going off is an earth fault.. Rule One " When operating one circuit and another goes on or off its an earth fault "
Having said that Rule Two says" with multiple faults tackle the simple one first and this will usually put the others right "
In the trade when doing relay problems we had some short jump wires so we could lift the relay out the holder and still get the test probes onto the connectors ..3 in of wire with male one end and female the other .....

Sadly however good the advice you are given you don't seem to want to follow it .

 

Well, now the confusion is complete. That IS an earth symbol. It is signal ground if you read the electric diagram.
If you look at fig 2.1 in the Electrical guide you will see the schematic called "Ignition switched ground distribution"

 

Good morning Y'all...

I want y'all to know I DON'T take your time, energy and willingness to share you knowledge and experience for granted. At all... That being said,,,

9 months ago Michael and I were casually looking at this... This is a hobby and supposed to be enjoyable... Then and now it's not a HIGH PRESSURE SITUATION @pistonbroke31 ,,,,, easy goes it man....

At the time, I got the trigger working reliably and stopped digging for a time - enjoyed the car and worked on a few other things - like installing a new VB separator plate, seals and tubes, and all the solenoids in the trans (great fun, lol). The transmission was full of water (literally) for years... We were getting ready then but never dug into the "coming from" ignition switch to the BPM side of things. The GO wire.. We were mostly looking at the other side, what was coming thru the trans via green wire,,, to the relay set up and then what was going on with the orange wire, then we stopped...

As y'all say, looking into what's going on with the GO wire thru the BPM,,, the various connectors, and to the ECU is the next right step. Thanks so much!

NOR,,, your directional with arrows is VERY helpful in giving me the path and order of information flow. I wasn't sure if the GO wire going into the BPM was necessarily the SAME as the GO coming out, but your mark ups and explanation really make it make sense. So thank you for that.

Looks like the way the ignition switch is set up is that they are ALL switched to ground to "activate" circuits and systems? Am I reading this correctly? Is that what the diagram from figure 2.1 describes?

If so, I will start following the GO wire and see what that turns up...


Does the triangle on BK indicate ground?

 

A LOT has gone on with this car... Some good, some questionable... One was finding a DEAD inertia switch that was filled with water. The way it was situated made it act like a little sealed bucket full of water, for years. It took me months to discover this problem. The way I "fixed it" was to remove it from the system. I did not replace the switch.

THIS IS FIG 2.1 from the Electrical Diagram...

At the time, I was wrestling with a completely dead PWM and OE fueling set up. For the time being I wired the pump directly but that produced way high fuel pressure and terrible trims. Super rich running. When I discovered the fault in the inertia switch I wired the WU wire directly to the RG wire leaving GU dangling capped...

At that EVERYTHING with the PWM fueling system came back on line, trims and fueling were perfect. My question is,,, could leaving the GU disconnected be causing my problems today? Trying to cover and explore all possibilities.

 

In the end you need to carry out the checks indicated in post 16 etc because you access the easy to test area (the relay) or you will not move forward.

 

It means logic ground - which for testing purposes is the same as ground. You can also see the earth eyelet marked above FC3BL - you can look that up to find where it is on the car if you ever need to find it, but again it shows it's a ground. Finally that octagonal symbol with a 1 in it is a switched ground symbol. So all that proves it's a ground.

You can also see the Not In Park switch on the diagram, which is the one I mentioned on the transmission itself.

By the way a test light is a better tool to use to check for voltage/ground rather than a multimeter as it puts a load on the circuit, so if for example you had a bad connection, a test lamp is more likely to show it.

 

Agreed it's an ignition-switched ground, so at ground potential when in position iii.

I came back to working around the starter relay as we didn't firmly establish previously whether the gearbox park/neutral switch was operating correctly (it may well have been under water).

I'm assuming for the moment that the BPM & ECM are happy with the security status as a system that could be circumvented by a simple relay bridge would hardly cut it.
The 2003MY service training guide gives a high-level description of the process.

If so then

• The ignition switch isn't grounding the green/orange wire at FC4-1 (or the BPM isn't seeing it at FC14-41)
• The BPM isn't signalling B+ on the other green/orange wire from FC14-72 through EM1-15 (or the ECM isn't seeing that at EM80-41 EM80-6)
• The ECM isn't grounding EM80-41 - the orange wire (or it's not reaching the relay pin 2)**

**obviously, we know that is the case at the moment...

EM1 I *think* is tucked up under the dash somewhere on the 4.2


And, hands up, dibbit & pistnbroke are correct that a simple (incandescent 12V bulb) test lamp would be better for this - my bad.

 

[QUOTE=dibbit;2529904 You can also see the Not In Park switch on the diagram, which is the one I mentioned on the transmission itself.[/QUOTE]

Great! And thanks, Man...
I do have a good test light.

Ok,,, for the Not in Park Switch - I hate to ask, but WHERE is that doggone thing on the trans... I'll wait for your reply and be googling at the same time. Thanks a bunch!

 

I *think* it's in the console. The EG says 'GEAR SELECTOR ASSEMBLY'

Do you get warning beeps if you try to remove the key when the shifter isn't in Park?

I confess I don't know what else it's for other than the door & seat modules on both sides are aware of it?

 

I think it is very important to not think of every possible problem at once, but focusing on one thing at the time, and try to rule out one possible cause after the other, from one end to the other, until there is only one thing left.
Forget the Inertia switch (for now, you absolutely should replace it, but the GU wire will only be grounded if the inertia switch is engaged, to give the BPM and ECM a signal to shut off almost all electrics except door locks and windows)
Forget the Not in Park switch until you have located the BPM, there you can easily test it if it is necessary.

Take out the glovebox, that is only a couple of screws, and see if you can locate the BPM,
Use your test lamp (much easier than a voltmeter IMO)
As mentioned earlier check pin 41 for ground when you turn the key, to rule out the ignition switch.
Check pin 58 for ground to check the not in park switch
And check pin 72 for ground when ignition key is turned to start, to see if the BPM is happy and sends the "request to start" to the ECM.
This will probably tell you (and everybody here that are trying to help you) exactly where the problem is.

 

​​​​​​Goodness knows I've had the BPM in and out of the car 7 different times since I've owned this doggone thing... Thanks for the play by play, I need that kind of reminder and guidance. Will do... And the test light will be leaving it's home in the XJS for all this!

 

Ha! The beeps...? That's a good idea. I'm not sure to be perfectly honest. We shall see in the morning. Is that all that the switch is for, ya think?

And yes, now that you mention it, I do remember the location as described in the ED.

One thing that happened a long time ago, and I hope it didn't destroy the function of the grounding mechanism inside of the BPM (of that's how they work), is that when I first got the car I basically removed and opened all of the modules I could to visually inspect, clean and check the condition... BPM for sure. What I DIDN'T know at the time was that the BPM is grounded (at least some of it) thru the body/casing of the BPM and it's attachment with 3 bolt studs and nuts to the body of the car in/under the dash. One time I was trying to start the car with the BPM either partly bolted in/up or maybe even not at all and portions of the BPM were touching a ground source, but not well and not securely... Could have done damage. Anyways, these are all of the wacky things I think about. And .00012% of the time, they end up being relevant, 😂...

Cars will make ya craZy!

You guys are the best. Thank you so so much!

 

I don't have the same transmission as you, but on my XKR with the Mercedes box, the switch is part of the transmission itself, so totally separate from the gear lever and selector mechanism in the car. It's just something to bear in mind as you trace this fault.

 

If you earth the orange wire it should operate the relay with the key in the start position... ( well you have 12v on the green so an earth on the orange will give you 12v across the relay coil. KISS