The only place for a coil spring is up Zebedee's arse
658 posts

csduetto: I believe you have already eluded to this but (having poked around inside various ECUs) it is always worth remembering that they usually tend to supply 'Electronic' Earth rather than Chassis ground anyway.
An ECU 'Electronic Earth' is often 'stabilised' via caps. etc of course.

-What usually tends to cause these Eth. 'outputs' to fail is -depending on the sensor- 12V/5V connected directly to them -ie without the (resistive) sensor- for a period of time: Similarly the 12V/5V 'regulated' supplies from an ECU can also be burned out by a persistent 'hard earth' - but some ECUs provide a 'resistive' Electronic Eth. too.

-Another unusual 'quirk' of ECUs is that some provide "Earth Pulses" too, for instance fuel injectors with 12V ('permanently') on one side...

Back on the 'million dollar question' however ECUs - rather that measuring a 'current draw' (or lack of it) - usually monitor the lack of sensor output (and/or any intermittent / persistently off-map / etc values of that sensor voltage/signal (depending on the particular sensor/type under consideration, obviously)....

If not wiring consider the EAS Valve Block driver ...... and/or the multi-way connector to it (notably for corrosion/damp) ?

PC38; Never quite that simple on a P38 of course but again this might help......


-and 'B'= eth. and 'OR' is the signal back to the BeCM

  • but note this diagram is for a later car than yours (ie. with the "Passive Immobiliser Coil" on the Ign. switch)

Incidentally does the Lynx actually allow you to disable the (other) Immobiliser so you can just use the (physical) key ?

PC38: back in #21 you were able to (temporarily ?!) resync. things with the usual 'fob button-press/luck-turn' sequence.... so there must have been power at the Rcvr. in order to do that (?). Or perhaps the power it is intermittent - ie. the plug-connector or cable is 'iffy' ? Thus the Rcvr. may well be getting power ok - but the signal not getting back to the BeCM ??
(You could only really investigate that at the BeCM with a 'scope - or you could try by just 'bridging' it with a wire of course)

Richard: IIRC the Gen 1 was an open PCB, Gen 2/a was also open board, Gen 2/b put the RF stuff in a can (which was clearly wishful thinking.....) and Gen 3 has that second small (RF) board perpendicular to the main board......? Still not quite sure how (or if) they got EMC Certification (Susceptibility) for either Gen 1 nor Gen 2s though...... Dire...

EDIT: Found the/a link from 10+ years ago about this scam/issue; https://mez.co.uk/page12.html
-and back then a GEN 3 was a mere £150+VAT !!

FWIW: The 'whole sorry saga' was reported thus
Until some of the contributors were banned.............

Well, after years of bu**ering about with my own 1995 (Gen 1 Rcvr. fitted) I just fitted a "12V Remote Relay" too: That allows me to turn the power to the receiver off/on .... when I want to use the car with the OEM fob... (Yes, that does mean using a second fob for said Remote Relay) but it was a cheap/effective fix - and also saved a fortune in (flattened) batteries due to all that irritating constant/random BeCM wake up of course......

PS: A reminder that the GEN 3 Rcvr. is physically different from the GEN 1 & 2 so if anyone buys a GEN 3 it is not just an (expensive) Green Dot of course. Ask them for photo inside the box .....!

Chris; No problem; Enjoy !

Hi Garvin, Will send one this week; Wonder what the supply issue is ?

Good to hear your battery is behaving now: P38s are like dogs, best not to show them any fear or they will bite !?

Found them....! So if anyone wants one just send an address... 6 going free (but UK only)...

  • but you all know how this works by now: if you are sensible enough to procure a spare/contingency item you then probably never need it, which is probably why I obtained 10 of them 10 years ago and never needed one ......

Garvin: Yes - the flying lead will foul on the spring if it is on the wrong side.... but £16 ? Good Grief (expletive deleted) !

Good, saves me mining then.... ! I wondered if the lower rating (0.1A) on the OEM item was part of the (failure) problem What's the part no/code for others, and price ? ( Either way it has to be better than paying £40 for a pair of catches and the switch may fail on that too ! )

Richard: That's what I thought, but it turns out those choices were actually very limited, particularly the sealed/flying lead variant/s (and frankly I don't know how if they are IP67 'sealed' they so often fail S/C either ..)

Garvin: Yes, I wonder what else they are used on ? I'll get digging, but it won't be until next week, and it's not so urgent (?)

Yes, it's a DC3C-Q5AA (ZF-electronics) - Had a 'forage' for them but may have to dig deeper (.....it was years ago)

Yes it is fiddly - mainly because the battery tray is in the way.... and I recall I took the headlight out too (but left the slam panel in place) when replacing mine: In fact when I noted that folks were only selling the catches in pairs for ~£40 I bought some microswitches instead (If I can find them I will send you one). Still rather 'bad practice' that the bonnet alarm can just be disabled by disconnecting it....

Judging by the numbers of bits of anti-friction rubber pipe etc I use here and there I am also a great believer in *preventative maintenance" too ( and I am usually muttering "did they not think that would be a problem after a few years ?" then assuming they don't care - of course)...

Good luck with the drain problem; These cars are haunted like that of course and just need exorcising at times.....

Richard: Yet other than the switch they look identical: ( Sorry, e-bay items #s 233208835164 and/or 333662784256 ) ?

Only JLR could have a 'safety' switch that 'works' if/when disconnected.......!
Or maybe they just expected to sell more replacement bonnets like that ?

Richard: Surely the catches are only 'handed' by virtue of the microswitch ? Thought the micro was N/C if bonnet closed ? That's why I suggested it was 'fudged' (eg wiring shorted). Good point about the EAS/Bonnet though....

Garvin: If unaware you can inhibit the EAS - ie. to isolate it as a culprit from the drain problem - by just pulling its 'timer' relay out (under the passenger seat - but after 18 years you probably already know that ! )

Yes, it's supposed to be on the Driver's Side catch - it's a small microswitch operated via that catch mechanism.... Perhaps it was broken and someone changed it for the type on the other side (without switch) and 'fudged' it ? There is (normally...) a two-wire waterproof-type connector located about 4 inches below that switch.... ( Don't think it is the cause of your drain though but you never know... )


That's also odd of - course - is the bonnet switch maybe shorted ? Guess your EAS will still work with it open too ?

Interesting... and the EAS can certainly be 'active' like that once you have locked the car - if/as it levels up but the 'click/clack' from its valve block is the real 'giveaway' for that if so... (?) Not meant to be a 'daft' question but are you actually closing the bonnet whilst reading these currents (as that might also upset things, notably the alarm) too ?

Marshall8hp wrote:

From a dealer perspective, when these cars were new, 6 weeks was seen as the maximum time that you could go and still have power to start. That is new truck and new battery. Second hand cars 4 weeks.

Frankly I would be amazed if they could manage 6 weeks in a dealers forecourt thanks to their (original) famous/hopeless 'oversensitive' Alarm/Rcvr. issue !

Richard: The LED Voltmeter is permanently on, visible from outside, and I use this same approach on numerous vehicles (either via the cigar lighter socket or the OBD connector). Particularly handy when these drains happen - apparently at random, à la p38 of course ! Over the years (on other cars) I have often found the most common problem is damp in the fuse-box, notably those that have the PCB-type multiple interconnect layers....

Garvin: I like your 'deductions' there - a partly-jammed/engaged solenoid might do all that (but, depending on the exact nature of the limited contact and current to the motor. it would probably discharge it rapidly (?) Guess you will have to pull the relay/fuse and put the car in the observation ward for further investigations ?!