Has your BCEM got insomnia? Mine had and here’s how I know…

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R

Rudolf

Member
Posts
32
Location
The Dark Peak, where you used to need a LR before
A little while ago I experienced the dreaded flat battery every Monday morning. The rest of the week was fine but park it up Friday night after a hard week and Monday saw it flat. This caused all sorts of problems including a lock out and loss of sync between ECU and key, that cost me a Syncmate, which by the way worked first time! However that’s another story. So having done my home work I’m sat in the car with an ammeter in circuit and sure enough, if you keep quiet the BECM drifts off to sleep and current consumption drops to a few milliamps…. But what’s this? She awake again, now asleep, now awake… ah we have the problem. Some one is shouting noisily in baby’s ear but who?
So, being a bit of a radio enthusiast I happen to have a scanning receiver, setting this up and working the door plip lots established the frequency it works on. Walking up and down the street, radio in hand, established a regular blip bang on the plip frequency at 10 second intervals, but where from? At which point a Luton van passed and the signal went away, so it had to be from across the Rd…..A quick word with my neighbour opposite revealed that he had a brand new shed and, not wanting anyone to enter without lawful cause, he’d installed a remote wireless alarm which, you guessed it, works on exactly the same frequency and my Landy!

So if you’re struck by the intermittent flat battery – BECM awake problem, see if you can borrow a scanner and take a walk up the street, failing that look over the garden fence for anyone with a new shed!

I love my Landy, never a dull moment……
 
Saint.V8 said:
So in this instance even a new RF unit wouldn't cure the issue, as they are still operating on the same freq.

What have you done to eliminate this issue??
Click to expand...
A new RF receiver almost certainly would cure the problem as it would not be swamped by random signals. The FOB emits a code, anything else on the same frequency that does not emit the correct code should be ignored.
 
Datatek said:
A new RF receiver almost certainly would cure the problem as it would not be swamped by random signals. The FOB emits a code, anything else on the same frequency that does not emit the correct code should be ignored.
Click to expand...
Ahhh...but surely the RF unit doesn't know the code, the BeCM needs to be woken up to check the code...

Surely if it is transmitting on the 433MHz or whatever the freq is, it will wake the RF Unit up so it can check what it has received with the BeCM...as the RF unit just acts to tell the BeCM it has received something and if it is correct.....
 
I think the YWY500170 Rf receiver would fix it,I've been fitting them since they came out,(Before even the main dealers knew the part number) and I've yet to have anyone come back with battery drain issues.I've been sleep testing an old 98my P38 this afternoon.(Dont see them very often now) I try to wake them up with a Defender 2 button fob after they have dozed off in 2mins 15secs... This one woke up which tells me it has the old RF unit fitted.The new ones will only wake up with the right key OR another P38 key - I've tried allsorts,but nothing else seems to wake them.
BTW,retail on the YWY500170 is now approx £202+Vat..... (I dont pay that much x Far....)
 
Saint.V8 said:
Ahhh...but surely the RF unit doesn't know the code, the BeCM needs to be woken up to check the code...

Surely if it is transmitting on the 433MHz or whatever the freq is, it will wake the RF Unit up so it can check what it has received with the BeCM...as the RF unit just acts to tell the BeCM it has received something and if it is correct.....
Click to expand...
The FOB sends a code, if it didn't any FOB would open the car, there is an initial compare of the FOB code in the RF receiver, if it's a valid code it gets passed to the BECM.
 
Sorry guys I didn’t mention the fix. Took the aerial off the receiver! It was the only choice short of moving house or burning down my mates shed. Since the alarm was transmitting on exactly the same frequency a new receiver would not have been of help

Be careful though… parking at a petrol pump under a steel frame canopy can result in the receiver no getting a key signal when it’s in the ignition….and there there be Dragons! Fortunately, I’ve now moved house, which admittedly is a little drastic but hey, it’s my Landy we’re talking about
 
Datatek said:
The FOB sends a code, if it didn't any FOB would open the car, there is an initial compare of the FOB code in the RF receiver, if it's a valid code it gets passed to the BECM.
Click to expand...
Ah I see - I knew the fob sent the code obviously....just though code check was carried out by the BeCM hence why it kept getting woken up in the earlier versions....maybe the new version stores the valid codes aswell as the BeCM so doesn't need to needlessly wake the BeCM each time to check the code it has received!!
 
Rudolf said:
Sorry guys I didn’t mention the fix. Took the aerial off the receiver! It was the only choice short of moving house or burning down my mates shed. Since the alarm was transmitting on exactly the same frequency a new receiver would not have been of help

Be careful though… parking at a petrol pump under a steel frame canopy can result in the receiver no getting a key signal when it’s in the ignition….and there there be Dragons! Fortunately, I’ve now moved house, which admittedly is a little drastic but hey, it’s my Landy we’re talking about
Click to expand...
As Dataek says the fob is coded,the Defender 2 button fob also works on 433Mhz - but the Becm will ignore it if it has the YWY500170 RF upgrade.433Mhz is free bandwidth so plenty of car manufacturers and others use it,door bells and weather stations etc.The upgrade has good enough filters to weed out anything it doesnt want,apart from the signal from a P38 fob it seems...
A no start at a petrol station is nothing to do with the steel canopy(Apart from possibly amplifying any signals) - its the GSM network transceiver hidden in the petrol price sign pillar corrupting the fobs signal.
 
Last edited:
JohnP38 said:
Be interesting to know how the RF receiver checks the Fob code as they are universal and do not have to be programmed to your fob and can be swopped between vehicles.:confused:
Click to expand...

This.

I guess the RF receiver can check to see if it has received a code (any code) of the correct format, and only wake the BECM if it knows it has a code that needs to be checked by the BECM to ensure it is the correct one for that vehicle. So all P38 fobs that send correctly formatted codes will wake the BECM, but only the correct code will unlock the car.

This way the RF receiver will be generic, ie work with all P38s without any coding, but the BECM will only be woken if a P38 fob signal is received.

But I am guessing.... I don't know if this is how it works.....

My P38 does not have the latest receiver, but disconnecting the aerial wire solved the battery drain problem completely so I have not bothered replacing it.

Cheers

Jerry
 
First off, 433Mhz is the header frequency, there are more than 100 sub frequencies fairly closely spaced, the early receivers would respond to all the subs.
Secondly as I understand it there is a recognition code which is common to all P38's, so the receiver will only respond to the right frequency + the recognition code, it will then transmit the rolling code to the BECM.
If this were not so, even the latest receiver would respond to any signal of the correct sub frequency and wake up the BECM, not only that, if there was no need of pre programmed recognition code, I would be able to supply a 433Mhz receiver for about £20!
 
JohnP38 said:
Be interesting to know how the RF receiver checks the Fob code as they are universal and do not have to be programmed to your fob and can be swopped between vehicles.:confused:
Click to expand...

The (new type) RF receiver just checks if the signal appears to be from A p38 fob (ie the correct prefix code) only then will it wake the BECM to check if it's YOUR fob and unlock the car.
 
My 98 4.6 has been going to sleep perfectly for the last 9 months, until this weekend . . . . so somebody in my neighbourhood has bought something :( So disconnected the antenna, which should help until I can save up for a new receiver.

But being the "diagnosing" type, I dug out the HP Scope to see what's going on. Sure enough with the antenna connected I can see regular bursts of data about every 30 seconds, which flattened a good battery to 4.5V overnight.

Reading through the old receiver threads gave me an idea. If the Mk3 receiver is generic to P38, then it must be using something in the data sequence to check for P38 Fobs. Given the rolling sequence that's specific to each BECM, the Mk3 RX cannot be using the actual vehicle code for the detection, so there must be a P38 header code in the sequence that triggers the Mk3 receiver to pass on the message to the BECM.

Maybe it would be possible using several Fobs to find the header string . . . . . and then program a PIC to look for this header. The PIC could then selectively pass valid P38 sequences to the BECM if the header matches. This would effectively enable the creation of an add-on chip for the Mk1 & Mk2 receivers, that would make them P38 selective. . . .. and probably cheaper than the Mk3 receiver.

All it requires is a decent sample of Fob Sequences from a few P38 owners to confirm the header sequence which by definition must be fixed or the Mk3 RX would work as described.

Any PIC programmers out there ?

Pete
 
pwood999 said:
My 98 4.6 has been going to sleep perfectly for the last 9 months, until this weekend . . . . so somebody in my neighbourhood has bought something :( So disconnected the antenna, which should help until I can save up for a new receiver.

But being the "diagnosing" type, I dug out the HP Scope to see what's going on. Sure enough with the antenna connected I can see regular bursts of data about every 30 seconds, which flattened a good battery to 4.5V overnight.

Reading through the old receiver threads gave me an idea. If the Mk3 receiver is generic to P38, then it must be using something in the data sequence to check for P38 Fobs. Given the rolling sequence that's specific to each BECM, the Mk3 RX cannot be using the actual vehicle code for the detection, so there must be a P38 header code in the sequence that triggers the Mk3 receiver to pass on the message to the BECM.

Maybe it would be possible using several Fobs to find the header string . . . . . and then program a PIC to look for this header. The PIC could then selectively pass valid P38 sequences to the BECM if the header matches. This would effectively enable the creation of an add-on chip for the Mk1 & Mk2 receivers, that would make them P38 selective. . . .. and probably cheaper than the Mk3 receiver.

All it requires is a decent sample of Fob Sequences from a few P38 owners to confirm the header sequence which by definition must be fixed or the Mk3 RX would work as described.

Any PIC programmers out there ?

Pete
Click to expand...
See your reasoning and wish you luck.:D I put a remote jog switch in the r/f to becm wire (orange). I now have two remotes, one to complete the circuit to the becm and then the r/r one to lock/unlock. upon completion of the operation the r/f to becm circuit is then broken and prevents any spurious signals waking up the system.
 
pwood999 said:
My 98 4.6 has been going to sleep perfectly for the last 9 months, until this weekend . . . . so somebody in my neighbourhood has bought something :( So disconnected the antenna, which should help until I can save up for a new receiver.

But being the "diagnosing" type, I dug out the HP Scope to see what's going on. Sure enough with the antenna connected I can see regular bursts of data about every 30 seconds, which flattened a good battery to 4.5V overnight.

Reading through the old receiver threads gave me an idea. If the Mk3 receiver is generic to P38, then it must be using something in the data sequence to check for P38 Fobs. Given the rolling sequence that's specific to each BECM, the Mk3 RX cannot be using the actual vehicle code for the detection, so there must be a P38 header code in the sequence that triggers the Mk3 receiver to pass on the message to the BECM.

Maybe it would be possible using several Fobs to find the header string . . . . . and then program a PIC to look for this header. The PIC could then selectively pass valid P38 sequences to the BECM if the header matches. This would effectively enable the creation of an add-on chip for the Mk1 & Mk2 receivers, that would make them P38 selective. . . .. and probably cheaper than the Mk3 receiver.

All it requires is a decent sample of Fob Sequences from a few P38 owners to confirm the header sequence which by definition must be fixed or the Mk3 RX would work as described.

Any PIC programmers out there ?

Pete
Click to expand...
There is a programmable chip with the header code, the manufacturer will not release details naturally. No need for PIC, just a data logger card for your PC, log the output data stream, note the section that changes with each FOB press, the other bit will be the recognition code:)
I think it's possible to graft a commercial reciever onto the existing recognition chip, not had time to play though.
 
i like all this talk on programing new chips sounds like the way to go, keep up the good work will watch with interest, totally beyond me
 
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