You need to break out the electrical diagram and trace back those functions that are not lighting (back from the dash). You know this: common ground; relays; fuses . . .

I will hazard a guess (especially since you know this stuff better than me), but a relay or fuse in either of the control boxes on the port side of the hood.

 

Found someone in the exact symptoms I have. Unfortunately they didn’t post a resolution and haven’t been on the forum in the 5 years since the problem.

Maybe this will clue someone reading this into something? Going to keep searching but figure I’d post this in the meantime:

https://www.jaguarforums.com/forum/x...-switch-50716/

 

Thanks Jhartz. Looking through the schematics some more now while I search the forums and Google.

Hmmm, dual linear switch does feed a module controlling fuel and ignition…

Mike

 

Do you have a second key? Try it and see if the results are the same. Sometimes the keys need to be reprogrammed.

It would have been nice to know what happened in that other case.

 

Yes, tried my valet key with the same results

I have the center console out and will remove the linear switch and open and inspect it. Also check the function of it.

Looks like it could be the BPM body processor module also perhaps?

Or it seems sometimes the lighting module in the gear selector can cause similar issues.

Mike

 

So I think I can bypass the linear switch and see if it is the problem.

It looks like I can feed +12V to the engine control module and ground the wire to the body processor module and the car should “think” the linear switch is in place and giving it a good signal to let the engine start.

Edit: Looks like that is just the Park or Neutral part of the switch. May not be the problem, or all of the problem.






Mike

 

OK, so odd things going on here when taking measurements.

I backbrobed pins 4 and 11 on the connector to the dual linear switch (used a safety pin on car wire harness side to get reading from pin while connector was attached to dual linear switch) and am getting readings that don’t make sense with the schematic and expected readings shown above.

Pin 4:

Pin stays hot (+12V) no matter if the key is in the igniton or not, regardless of ignition position (OFF, ACC, ON) and regardless of shifter position, or any combination of those.

IMPORTANT - Pin 4 also stays hot on the CAR harness side even when the connector is separated from the dual linear switch. In other words, the INPUT from the body processor module is OUTPUTTING +12V always, even if the key is not in the ignition.

Seems to me this would indicate the body processor module is bad?

Pin 11:

+12V when key in ON position only. However, it stays at +12V regardless of shifter position when the key is in ON. Looks to me like it should only be +12V with key ON and in P or N according to the table above?

Also, pin 11 never connects to ground (connector attached to dual linear switch) regardless of ignition switch position or shifter position or combination of either.

Seems like this would indicate the dual linear switch is bad?

It seems a strange coincidence both the BMP and DLS would fail simulataneously. Unless the +12V feed to the DLS output by the BPM fried it I guess….

I’d welcome any thoughts or suggestions on what to test next, or on my test methodology so far.

Thanks,

Mike

 

Pic of harness reading +12V at pin 4. Ignition OFF, key in my pocket:

 

The nearest I've met to this was a damaged major loom (in an STR). Had been pierced and then water got in and corroded the wires.

On the STR it runs up high in wheel arches (wells?) and behind front bumper - sorry don't know where on these cars.

With so many damaged wires and some cross-connecting (cross-shorting) the outcome was truly weird.

 

Edit: The following are all with the ignition OFF and key in my pocket.

So I pulled the glove box and checked the pin 7 at the body processor module (BPM) and without the DLS connected I get +12V at the connector on the BPM.

I removed the connector from the BPM and checked for continuity between pin 7 @ the BPM connector and pin 4 @ the DLS connector and got continuity/

I checked pin 7 @ the BPM connector with the connector removed from the BPM and did NOT find +12V, so that would seem to indicate that the BPM is outputting +12V on pin 7. It looks to me like that should be an input and not have a voltage of its own, or am I misinterpreting things?

Thanks,

Mike

 

I am not sure, but I would not condemn the BPM yet. Many of the car's circuits are grounded for the true condition. In other words, there is a voltage sourced from the module that the switch pulls to ground. The designation of the switch in the schematic would indicate that is the case in this circuit, with both non ground terminals labelled "P,N".

However, that begs the answer, why does the switch not ground pin 4 when you are in neutral, and not ground 11 when you are not in Park or neutral?

Notice the ACTIVE and INACTIVE columns in the chart at the bottom of the schematic.

 

Well I seem to have made the situation worse. I didn’t disconnect the battery before removing the BPM or reconnecting it.

Nor I have a rapidly flashing red light on the shift bezel and I can’t lock the car.


I tried disconnecting the battery, removing the BPM harness and reconnecting it and then reconnecting the battery with no change.

Anyone care to tell me the solution while I try to search for it?

Thanks,

Mike

 

All plugs in tight? Is the ground connected well? Are the several fuses feeding the BPM and ECM all good?

 

You get some bonus points today sparkenzap.

Just went out and messed with the Jag again. I had the BPM grounded laying against a chassis ground. I was able to make the light stay on or go away by how hard I pressed against the ground.

Removed battery cable (I do learn) and removed BPM cable, mounted CPM with the 3 studs and nuts, put back BPM cable, reattached battery cable.

Light is gone, hallelujah. Of course battery is about dead now though. Hooked Jag up to running wife’s car and central locking works now. After the “will turn over but not fire” episode, central locking would not work. Of any significance to anyone?

So no change in the original behavior now. Same scrolling messages, same lack of dash warning lights when first turned to “ON”, and no fuel or (as far as i can tell ) spark.

I’m looking for a replacement BPM. Anyone have one close enough to the follows VACTS to work for me they’d like to sell?

LNG2500AC/046

Thanks,

Mike

 

Well, lets go back to the linear switch. Is it really not changing state according to the chart?

 

I’ll doublecheck again tonight.

The linear switch is the easy part to get though, should be able to get one ovenighted from a lot of places. More worried about the BPM since I need to find one that matches, or is close, to my VCATS. Maybe I just replace both.

If the Jag wasn’t my primary DD I wouldn’t be so concerned, but I don’t want to pile miles on the M3 or drive it in the rain.

Mike

 

I do not think you have found a strong indication of a bad ECU or BPM ...Yet! Possible, but lets prove it is doing something different from what it is supposed to.

The security functions come to mind, as well as a missing power source or sensor, like the linear switch.

Are you SURE fuse #16 in the LH heelboard is good and that you have power on circuit 33 (pin 1 of the fuel pump relay) when the key is on?

 

Maybe it is time to toss the caution flag; maybe even back up, entirely. In three years of digesting this forum, the X100 forum for engine related issues, ten years on the LR3 and RR forums (same engine and electrical architecture) I do NOT remember ever seeing an issue with BPM or linear switch and very few ECU issues. Instead, lots of bad relays, bad fuses, bad key transponders, set inertia switches, bad fuel pumps. To my mind, those are better rabbit holes than the one your down.

 

Yep. And so far, there is NO indication of a bad module. Not yet!

 

You may be correct about the module running a signal to ground through the linear switch to sense what position it is in.

But the switch was also not changing state when measuring resistance at the connector pins and physically moving the contacts in the switch.

I included the active and inactive chart because I was showing I was taking into account the ignition switch position while I was testing.

I was getting P0705 out the wazzoo in the past, and if I’m not mistaken that’s a code the the linear switch (or being out of alignment perhaps). And when I was getting the “gearbox overtemp” error I could rake the shifter from P to 2 and back a few times and usually clear it.

I also replaced both pumps a year or two ago, so they only have ~10k miles on them.

I ordered a new linear switch, so we’ll see if that fixes things.