Sorry, I haven't been about earlier... I'm currently being pulled from pillar to post on this job - and as such haven't had time to sit down an actually look at much on any of the forums, emails, facebook groups...

The passive immobilisation part of the BECM - which is switched on/off by toggling the 'IMMOBILIZER' option in the BECM settings works as Sloth mentioned by pulsing a coil around the ignition and this then activated the fob to transmit an unlock code. From what I have noticed, this is initally triggered by the 'Key in' switch in the ignition barrel... so the BECM notices the change in state in the key switch, so knows the key is in the ignition. It will then pulse the ignition coils, get the fob to transmit a code, and disable to immobiliser - if it has enabled itself.

I call what Morat mentioned as a 'limbo' mode - where it's not in a total EKA state as the doors lock/unlock - but the immobiliser is still on - most usually because the passive part has timed out (and then usually as mentioned, it will re-mobilise itself with the key in the ignition). Entering the EKA should make it so that it will start, but it can be hit and miss if it doesn't think it's in an EKA lockout mode.

A note on entering the EKA with a Nanocom (I haven't had time yet to watch the video Morat put up) but the communication with the BECM needs to be done with the IGNITION OFF - rather than hooking up to it with the ignition is already on - the BECM communicates better with nothing on in the ignition for some reason.

Also as a side note, before I sign off again and go to get on the plane.... the passive coil (whilst it is only single direction communication to pulse the fob, it won't talk back to the BECM through these wires)... isn't just the coil, hooked up to the vehicle wiring. There is a small PCB in there, with a bunch of components too - which I don't know exactly what they do yet - I want to try and find out, as the coil on my P38, is intact I've found, but something has burnt out on the board - which is why my passive immobiliser coil isn't working properly (it wouldn't pulse the fob, and fob wouldn't transmit)..

Right, better go and get ready to board the plane...

Will hopefully have a day off soon so I can try and catch up properly!

Marty

Fascinating stuff Marty, thank you! Good catch on the BECM communication - I did it in posn 2 on the key so that can't have helped. Oops.
and is it safe to assume that the fob needs a battery to transmit back to the coil? From the behaviour I saw I guess it does actually have to transmit rather then being passively detected in some way.
Anyway, it's happy now but the back of the fob does need to be tweaked right round clockwise to make sure the contacts engage otherwise it's "no red light, no locky locky" and frustration ensues. It's better than it was with the rubber grommet in place, no amount of tweaking could make the fob light up when that was still in.
Best of luck with the rest of the trip, when you get back you'll find that winter is well and truly here!

Well, the flight is delayed, and with any luck I'll still get to Philadelphia in time to make the connection to Dallas..

Yes, the battery does need to be in the fob for it to pick up the pulse from the coil and then transmit the unlock code. No battery in fob basically just makes it a key blade with a big shell on it.

Interesting that it works without the rubber O-ring, but not with....

Maybe the springy contact on the side of the PCB is missing the little bit of rubber under it to hold it up enough so that it doesn't make contact with the extra thickness of the o-ring under the cap...

You mean there should be a little piece of rubber under the contact? I put one in mine as I though it didn't seem to have a lot of tension to make a good contact. I though the contact had just lost a bit of springiness and a bit of rubber would give it a helping hand......

I vaguely remember seeing a post somewhere where it was suggested that using a combination of the 2025 and the next size up in thickness, 2032, made for a better contact. Bonus of greater capacity as well.

Aha, I've got the mixture in mine, was spitting feathers when I changed, as I'd bought the 2032, but not the 2025, sounds like the first thing the previous owner got right,,

As Marty states it looks like the coil around the ignition just sends a signal to instruct the fob to talk back to the BECM (and if this is not done via the coil then it must be via the RF 'parcelshelf' receiver..?). The PCB connected to the coil must be responsible for oscillating the field to the coil so that it can inductively communicate to the fob then.....(?) If that is correct then this can only occur if the fob has batteries installed, too !
..............................................................................................................................................................................................................
Note: This is for the TD5/Defender but it is probably similar to the P38 design:

Passive Immobilisation

Passive immobilisation occurs when the key is removed from the ignition switch and the drivers door is opened,
after a period of 30 seconds the engine will become immobilised. If the ignition is turned off or the key is removed
from the ignition switch and drivers door is not opened, the engine will become immobilised after 5 minutes.

The passive immobilisation system operates in conjunction with the transponder coil located around the ignition
switch barrel. The transponder coil emits an electro magnetic waveform signal which excites the remote handset
into transmitting a remobilisation signal. When remobilisation is requested, the anti-theft alarm ECU transmits an
appropriate code to the ECM on Td5 models or the engine immobilisation ECU on 300Tdi models.

Active immobilisation

Active immobilisation is only invoked when the vehicle is locked using the remote handset. Active immobilisation
performs the same engine disable functionality as the passive immobilisation previously described, but includes
full CDL and activation of perimetric and volumetric alarm modes.

Forgot to add this, too:-

On 1997 and later models (all markets?), "friendly synchronization" is provided whenever the key/remote is inserted into the ignition. The passive immobilization coil around the ignition barrel activates a pickup coil in the remote, causing the remote to transmit an unlock signal to remobilize the vehicle.

• Again from: http://www.rangerovers.net/repairdetails/becm/alarm.html

As '95, '96 and '97+ models deploy this mechanism differently it could explain why the Driver's Manual/ETM/Workshop manual differ as described in that link.... Under "Resych.... Mystery"

On pre 1995 models, I don't think the passive sync was actually enabled, even if it was fitted/shown in the manual. My old '95 never had anything like passive sync in it - just do it in the door and away you go..

Yes, the receiver coil is excited by the transmit coil around the ignition - and yes, this does send an unlock code from the fob, and is received at the RF receiver. There is NO other RF/transponder mechanism on the P38 for the receiving of code/signals from fobs. The parcel shelf RF receiver is the only RF link the BECM has for incoming transmissions.

Yes, I think there should be a small black bit of what looks like rubber under the single separate contact in the key fob. I remember seeing a picture of it somewhere on RR.net ages ago. If I can find it again, then I will put a copy of the picture, or a link to it up..

Guessing you meant "pre-1996" Marty but I know what you mean; Mine is '95 and yes there is no coil fitted (and IMHO there is a lot to be said for that !).

• Not sure just what components are blown on your coil PCB, it probably is not very complicated - as it will just instruct the fob to acknowledge a basic low power/frequency encoded pulse, but in LR-World this would still likely involve an ASIC (?) so not easy/possible to repair/replace either... Any useful markings on it ?

Yes, meant pre '96.... this getting up early and being in a venue all day malarky is getting a bit boring! Think I'll be giving my hunk of aluminium in the garage a hug by the time a get home, as the simplicity of it will be a stark contrast to some of the bollocks I'm dealing with here...

I did take some pics of the PCB board for the coil, but can't find them at the moment... I'm planning on trying to fix mine up and see if I can get the passive immobiliser/friendly sync working properly on mine again - not that I'm in a hurry for it!

You're dealing with Yanks........... what do you expect?

This thread is priceless, as is the whole "pub" :-)

I am in despair as I have been fighting the damn battery lid on the fob, so far just mangling the darn thing, which I had already replaced few years ago. It seems every battery change goes along with a battery lid ... shucks.
Next attempt will be the twin-hole drilling and pliers as indicated here ... really a bugger.

Great to have always someone ahead with a solution to every problem!

I guess there's a reason Island sell the batteries with a new lid and grommet!

Ahh happy days :) Thanks for the thread resurrection!

What a drag! Drilling and pliers were successful, but a lot of struggling!
The culprit was the metal part on the lid to close the batteries' circuit, it had dislodged and thus blocking the movement.
The replacement lid would not fit with the o-ring, discarded and hops it fits.
Everything works, albeit randomly (1 time in 5) decided "not" to work so I have to use the key. No big deal, I least I got rid of the damn chime and key battery low message ...

Send it to Jon.......
https://www.ebay.co.uk/itm/265688990980

Ferryman wrote:

I've seen Marty replying to someone where he states that the the small lip that goes along both batteries might contact both, resulting in only 3 volts. He says put a small strip of insulating tape on the battery where the lip passes to avoid this.

Aha - interesting idea.. that cd explain alot