P38 RF Receiver to BECM

martyuk · Nov 2, 2018

Sorry, just seen that I've been tagged in this... been away working.

In short - yes, the 3rd gen RF receivers can fail - I've got about 3 or 4 of them here which are faulty, and I'm looking into if it's something simple to repair, or whether they are totally dead.

It won't be a BECM fault - and I wouldn't go swapping things about just for the sake of it. The fact you can use an earlier version receiver and sync the key says that it isn't a BECM issue. I'm almost certain it's receiver related.

Myself and a mate/fellow P38 owner have finally managed to make an alternative for the gen3/green dot receiver - which is an inline plug and play RF filter that does the same job as a gen3 receiver but for a fraction of the price. I've put a link below to information about it, and also a video link to my mate doing a bit of a run down on some of the RF interference issues.

I am happy to have a look at your gen3 receiver and see if it has the same issues as the others I've got here that are faulty - but it wouldn't be until December now as work is pretty crazy for the next month and I'm not going to have a lot of spare time at home.

Link to info about the RF filter:
http://p38webshop.co.uk/index.php?route=product/category&path=84
Link to video on P38 RF interference etc:

Disclaimer - the webshop link is my web store for P38 parts I work on. I am posting here for your information, I don't intend to 'plug' our solution to RF issues on the P38, it doesn't bother me one way or another if people order them!! We just wanted to try and crack the problem, and offer a solution that didn't involve handing over nearly £300 to LR!! I don't work on P38's or parts full time, I have a day job aswell (hence why I've only seen this now) but I'm happy to answer any questions about the RF filter if there are any. It does work, it's not a con, and you can use it with either of the MK1 or MK2 receivers with no problems.

dubloman · Nov 2, 2018

Hi

Just got back from a meeting with Paul (Wazzajnr) who kindly plugged in the nanocom to see what we could see.

He has helped me in a bypass (Thanks Paul) you know the bypass has helped.

The things that we discovered are that it's weird, the key seems to be sending but the signal is not always getting to the BECM, so what I am going to do it clean the related plugs and pins (Thanks again Paul for helping ID the correct plugs and pins for the job) but it could also be that the micro switches in the door mech are about to fail or have an intermittent fault and this is why it works and then stops.

Paul suggested contacting MartyUK to ask about his exchange unit for the door as this is the 2nd thing I need to check before trying the door microswitch unit. So, I will drop you a line about the unit in the door.

I have looked at the fob filter and it looks a great device but if the issue is with the plugs and pins or the microswitches in the door and my green dot unit is still good then the filter should not be needed but it is a great deal cheaper than replacing the RF receiver (green dot) so will keep that in mind.

I will stick with the BECM unit I have and take the advice of those more knowledgeable on P38's than I and not change out the BECM but instead try to find out the cause of the problem as Paul said it might be nothing to do with the BECM.

At least I can unlock and lock the car and start her and drive away without all the hassle at the moment but finding the reason for it being weird will need a bit more time I feel

Thanks

Dave

Wazzajnr · Nov 2, 2018

One thing you learn very quickly with p38's is take things a step at a time and listen to the excellent advice handed out on here.
Marty is probably one of the most knowledgeable on how the alarm and key system works.

@martyuk I, like you, don't think it's the BECM however I also don't think it's the rf receiver as the symptoms seem the same with all 3 that Dave has.
I assume the signal from rf to BECM is a data signal rather than just a 12v pulse?
I got it working a couple of times then it would loose sync very soon afterwards (2-3 presses of the fob)
Works fine on the key and at least he doesn't have to enter eka every time now.
Just seem to be able to sync it, get one or two cycles on the fob then need to enter eka and resync in the door before the fob works again.

Datatek · Nov 2, 2018

Wazzajnr said:
One thing you learn very quickly with p38's is take things a step at a time and listen to the excellent advice handed out on here.
Marty is probably one of the most knowledgeable on how the alarm and key system works.

@martyuk I, like you, don't think it's the BECM however I also don't think it's the rf receiver as the symptoms seem the same with all 3 that Dave has.
I assume the signal from rf to BECM is a data signal rather than just a 12v pulse?
I got it working a couple of times then it would loose sync very soon afterwards (2-3 presses of the fob)
Works fine on the key and at least he doesn't have to enter eka every time now.
Just seem to be able to sync it, get one or two cycles on the fob then need to enter eka and resync in the door before the fob works again.

The output of the RF receiver is indeed a data stream.
I still think the problem is likely to be either corroded BECM connectors or door lock micro switches, the latter being more likely IMO.

Wazzajnr · Nov 2, 2018

The micriswitches was my first feeling but then the CL works perfectly on the key every time which makes me think it is corroded connections.
My suggestion to Dave was check connections first as it only costs time then if that don't fix it, get a refurbed latch pack.
If that still doesn't fix it time to dig deeper.

Grrrrrr · Nov 2, 2018

Brilliant work. Well done Marty. If I didn't already have a gen 3 receiver I'd have one. That's half what I paid for mine as well.

What was waking mine up and burning the locks out was my outdoor weather station. Others seemed to have issues in some petrol stations although what caused the issue there is anyone's guess.

martyuk said:
Sorry, just seen that I've been tagged in this... been away working.

In short - yes, the 3rd gen RF receivers can fail - I've got about 3 or 4 of them here which are faulty, and I'm looking into if it's something simple to repair, or whether they are totally dead.

It won't be a BECM fault - and I wouldn't go swapping things about just for the sake of it. The fact you can use an earlier version receiver and sync the key says that it isn't a BECM issue. I'm almost certain it's receiver related.

Myself and a mate/fellow P38 owner have finally managed to make an alternative for the gen3/green dot receiver - which is an inline plug and play RF filter that does the same job as a gen3 receiver but for a fraction of the price. I've put a link below to information about it, and also a video link to my mate doing a bit of a run down on some of the RF interference issues.

I am happy to have a look at your gen3 receiver and see if it has the same issues as the others I've got here that are faulty - but it wouldn't be until December now as work is pretty crazy for the next month and I'm not going to have a lot of spare time at home.

Link to info about the RF filter:
http://p38webshop.co.uk/index.php?route=product/category&path=84
Link to video on P38 RF interference etc:

Disclaimer - the webshop link is my web store for P38 parts I work on. I am posting here for your information, I don't intend to 'plug' our solution to RF issues on the P38, it doesn't bother me one way or another if people order them!! We just wanted to try and crack the problem, and offer a solution that didn't involve handing over nearly £300 to LR!! I don't work on P38's or parts full time, I have a day job aswell (hence why I've only seen this now) but I'm happy to answer any questions about the RF filter if there are any. It does work, it's not a con, and you can use it with either of the MK1 or MK2 receivers with no problems.

Datatek · Nov 2, 2018

Wazzajnr said:
The micriswitches was my first feeling but then the CL works perfectly on the key every time which makes me think it is corroded connections.
My suggestion to Dave was check connections first as it only costs time then if that don't fix it, get a refurbed latch pack.
If that still doesn't fix it time to dig deeper.

Good advice, but my project car had the same symptoms, worked fine on the key but intermittent on the FOB, that was due to the drivers door lock completely gummed up and sometimes failing to operate the micro switches.

dubloman · Nov 2, 2018

All the advice appears to be pointing to the two things, Paul suggested them today and others have on here.

The advice and help received here are 2nd to none as with any intermittent fault you can only troubleshoot it when it fails. I will clean the BECM plugs and pins as a matter of urgency then if the problem persists look to remove/clean the latch mech and if that does not fix the problem I will be buying a latch pack but I have looked at your site Marty and it says you are no longer doing the exchange units (I can understand why) from Sept 2018. If this is the case I will have to buy one as listed.

As others have said it is highly likely to be the cause but as with anything as complex as the P38 you can cross your fingers and hope that you have fixed the problem, if not dig deeper as suggested.

I will of course feedback results to what happens in this case and hope that by doing this I can help others fix similar problems

I must thank everyone that has commented and given advice and the generous time of Paul who has deactivated the need to put the EKA code in each time I turn off the engine, as you will appreciate I know the EKA code as well as I know my date of birth......lol, plus paul has taken the time out of his busy day to help me out....................don't eat all the choc hobnobs in one sitting....lol..........Thanks for your help your are a star

Thanks

Dave

sassanach · Nov 4, 2018

Grrrrrr said:
Brilliant work. Well done Marty. If I didn't already have a gen 3 receiver I'd have one. That's half what I paid for mine as well.

What was waking mine up and burning the locks out was my outdoor weather station. Others seemed to have issues in some petrol stations although what caused the issue there is anyone's guess.

well ive bought one simply on reading martyuk post.i have a gen 2 receiver with which i have had no problems yet,but a solution at that price cannot be ignored.

dubloman · Nov 4, 2018

Hi Everyone
As promised I am reporting back to the group
I have attached pictures of the plug that Paul and I looked at that relates to the RF reciever plug in the BECM.
As you can see I have no issues with the pins or the plug
The continuity test is next but given the fault is intermittant (now not doing anything) I would assume that the wire between is faulty but I shall rule out that when I test.

Continuity test shows no signal so I am either not getting a good contact at the rf end (stripped wire back at becm) I will have to strip wire at rf end and retest

martyuk · Nov 4, 2018

Erm - You've got the wrong connector there...

The RF receiver feeds into the BECM on C1285, which is the 20 way Blue connector (next one to the left in your picture). The wire you're after is the Orange/Red wire, which goes into pin 6.

I could be wrong, but from what you have described - your drivers door latch appears to be working as intended. If you can enter the EKA successfully, then this uses the Central Locking and Key microswitches - which are the usual ones to fail. It is worth checking them though (I have a test sheet on my website in the technical information section) - but also worth testing with a multimeter on ohms setting and seeing what the resistance reading is. I've seen a few in latches recently which on a continuity check show they are switching OK - but the resistance when closed is 100-200 ohms, which is sign of water ingress/corrosion in the switch - as the resistance when closed should read 0-2 ohms (depending on meter etc).

Regarding the RF receiver - the signal sent from the receiver to the BECM is a pulse train of data which in a 'normal' (ie single button press, not a press and hold) of 140ms in a square wave. You can't reliable see these pulses on a standard multimeter, but if you measure on voltage range, between ground and the Orange/Red wire (with it plugged into the BECM/Receiver - so back probe the connector with a thin piece of wire is usually the best way of testing) you should get a reading of around 10V when nothing is happening and then observe a brief 'blip' in the voltage dropping down to maybe 6-7v when a button is pressed on the key fob. What you read will depend on how quick the meter is at registering the change in voltage from the pulse train.

A corroded wire or connection could indeed cause issues as it's a digital signal, so corrosion etc in the wire can affect the levels of it and cause it to be read improperly at the BECM end.

The other thing worth looking at - if it does it with ALL receivers (I thought it was just with the 3rd gen from when I read it initally) then it could also be the key fob that is acting up. I've seen it before where when the battery connections are dirty or a bit tarnished, or the remote batteries are getting low that the data sent from the fob can be inconsistent. If it is happening always in one location, then it is also possible that RF interference is causing the received signal to be garbled a bit before it even makes it into the receiver to be processed (in the case of the 3rd gen) so it is then stopping the signal from being sent on. And in the case with the 2nd gen receiver, it's passing it onto the BECM, but it isn't being decoded correctly.

As a slight aside on that note - we sent out one of the pre-production RF filters to an owner for testing, as he was getting some really weird issues come up. Along with the normal BECM not sleeping and battery drain, he was coming out in the morning to messages on the dash like "Alarm triggered" (even though it hadn't gone off) "Ignition Tamper", key not being synced, and some other corrupted info in the BECM. He works in RF and ended up finding out the culprit was a faulty central heating thermostat that was on 433mhz aswell. He changed it out, but before he did we asked him to try one of our filters inline as a test for us, and the word came back a couple of days later that the key fob stayed synced, he had no weird messages on the dash, and it started first time after not having been driven for days - rather than coming back to a nearly flat battery. The main moral of that anecdote (other than it proving to us the filter worked!) is that RF interference on the same 433mhz band can so some really weird things to these vehicles! The 3rd gen receiver *should* stop this interference getting to the BECM and waking it up (as our filter does) but it won't necessarily stop the interference messing with the received signal to the receiver in the first place.

Hope you manage to get it sorted soon!

@sassanach - Thank you for the order! It should be sent out in the next couple of days.. my mate is finishing assembling/testing it this weekend and will get it sent out to you, as I'm off away working again this week... It is nice having someone else working on the project with me, as it means we can keep them available even when I'm not home

dubloman · Nov 4, 2018

Hi Marty

Thanks for the correction, it was an estimate that the plug I checked was the correct one, I will go and look again and see what can be found, weather permitting.

Lots of info being given and lots to take on board.

I think the best thing is to check the correct plug first and then take all your great advice step by step to see if it can be resolved.

As promised I will report back here with my findings. I will be sure to look at getting one of your filters, but I think going through the process in a logical methodical manor.

Cheers
Dave

dubloman · Nov 4, 2018

Another update following Marty's advice

Attached are the pictures of the plug and pins, again they are clean, tested continuity and I get a good tone.

I put the green dot RF receiver on and nothing (I assume this has failed) I put the blue dot on and synced the key and as before I get one or two actions on the door before it stops. If I do (key sync) open first the lock I get the fob to open the car and lock it but if I do lock first, then open (key sync) then I only get to lock the car by the remote. I do the sync again and I get the same. With the green dot unit not playing and intermittent faults could it just be the RF unit? Or other devices are using the 433 signals and causing a problem

I do have a key fob signal reader and it says my key is putting out the signal of 433/433.5

I am now going to read the advice from Marty and see what else happens on the multi-meter readings etc

I know this is a big ask Marty, if I were to buy a RF filter and it did not fix the problem could I do it fix or return? As I am spending money like water on this problem and not getting any further forward

Dave

dubloman · Nov 4, 2018

Update

Wire in the O/R plug on the blue plug and I get 10.55v reading when nothing is happening

Then when I press the remote I do get a drop in voltage to what appears to be 6 or 8 volts

Not sure what that is telling you Marty but it just confuses me more.

I assume this is saying that the RF unit is sending the pulse down to the BECM and then the unit is not faulty but the signal is causing the issue

Thanks
Dave

dubloman · Nov 4, 2018

Additional

Voltage test on green dot 10.5v static no change when key fob pressed
Voltage test on 1st blue dot 10.5v static 6 to 8 v when key fob pressed
Voltage test on 2nd blue dot 10.5v static 6 to 8 v when key fob pressed

Any thoughts?

Datatek · Nov 4, 2018

Datatek · Nov 4, 2018

martyuk said:
Erm - You've got the wrong connector there...

The RF receiver feeds into the BECM on C1285, which is the 20 way Blue connector (next one to the left in your picture). The wire you're after is the Orange/Red wire, which goes into pin 6.

I could be wrong, but from what you have described - your drivers door latch appears to be working as intended. If you can enter the EKA successfully, then this uses the Central Locking and Key microswitches - which are the usual ones to fail. It is worth checking them though (I have a test sheet on my website in the technical information section) - but also worth testing with a multimeter on ohms setting and seeing what the resistance reading is. I've seen a few in latches recently which on a continuity check show they are switching OK - but the resistance when closed is 100-200 ohms, which is sign of water ingress/corrosion in the switch - as the resistance when closed should read 0-2 ohms (depending on meter etc).

Regarding the RF receiver - the signal sent from the receiver to the BECM is a pulse train of data which in a 'normal' (ie single button press, not a press and hold) of 140ms in a square wave. You can't reliable see these pulses on a standard multimeter, but if you measure on voltage range, between ground and the Orange/Red wire (with it plugged into the BECM/Receiver - so back probe the connector with a thin piece of wire is usually the best way of testing) you should get a reading of around 10V when nothing is happening and then observe a brief 'blip' in the voltage dropping down to maybe 6-7v when a button is pressed on the key fob. What you read will depend on how quick the meter is at registering the change in voltage from the pulse train.

A corroded wire or connection could indeed cause issues as it's a digital signal, so corrosion etc in the wire can affect the levels of it and cause it to be read improperly at the BECM end.

The other thing worth looking at - if it does it with ALL receivers (I thought it was just with the 3rd gen from when I read it initally) then it could also be the key fob that is acting up. I've seen it before where when the battery connections are dirty or a bit tarnished, or the remote batteries are getting low that the data sent from the fob can be inconsistent. If it is happening always in one location, then it is also possible that RF interference is causing the received signal to be garbled a bit before it even makes it into the receiver to be processed (in the case of the 3rd gen) so it is then stopping the signal from being sent on. And in the case with the 2nd gen receiver, it's passing it onto the BECM, but it isn't being decoded correctly.

As a slight aside on that note - we sent out one of the pre-production RF filters to an owner for testing, as he was getting some really weird issues come up. Along with the normal BECM not sleeping and battery drain, he was coming out in the morning to messages on the dash like "Alarm triggered" (even though it hadn't gone off) "Ignition Tamper", key not being synced, and some other corrupted info in the BECM. He works in RF and ended up finding out the culprit was a faulty central heating thermostat that was on 433mhz aswell. He changed it out, but before he did we asked him to try one of our filters inline as a test for us, and the word came back a couple of days later that the key fob stayed synced, he had no weird messages on the dash, and it started first time after not having been driven for days - rather than coming back to a nearly flat battery. The main moral of that anecdote (other than it proving to us the filter worked!) is that RF interference on the same 433mhz band can so some really weird things to these vehicles! The 3rd gen receiver *should* stop this interference getting to the BECM and waking it up (as our filter does) but it won't necessarily stop the interference messing with the received signal to the receiver in the first place.

Hope you manage to get it sorted soon!

@sassanach - Thank you for the order! It should be sent out in the next couple of days.. my mate is finishing assembling/testing it this weekend and will get it sent out to you, as I'm off away working again this week... It is nice having someone else working on the project with me, as it means we can keep them available even when I'm not home

I can assure you that the latch micro switches may fail to operate correctly from the FOB, but work perfectly from the key, I have had exactly that condition on my project P38.

Datatek · Nov 4, 2018

dubloman said:
Additional

Voltage test on green dot 10.5v static no change when key fob pressed
Voltage test on 1st blue dot 10.5v static 6 to 8 v when key fob pressed
Voltage test on 2nd blue dot 10.5v static 6 to 8 v when key fob pressed

Any thoughts?

From that it would seem that your green dot receiver is faulty.

dubloman · Nov 4, 2018

Datatek said:
I can assure you that the latch micro switches may fail to operate correctly from the FOB, but work perfectly from the key, I have had exactly that condition on my project P38.

So "Datatek" you are saying that the fault may still be the door latch and the microswitch?

Never having stripped out the door latch mech I understand that there are a number of types of door latches and some are more prone to fail than others?

However, it is said that if you can put in the EKA code, it is unlikely to be the door latch microswitches, but saying that I am going to investigate all areas to ensure that this is not overlooked in trying to fix this problem.

I have checked the plug and pins on the BECM and tested the continuity as well as tested the voltage and voltage drop on all 3 units, I would agree that the green dot unit has failed.

I have just got back from a remote location to remove the possible interference from the local issues and I still get the same issues as explained in my previous reply. This would suggest that another issue exists and it might be

The door latch (Will strip the door down tomorrow)
The RF Receiver (Need a filter)

Could it be anything else?

Thanks
Dave

Datatek · Nov 4, 2018

dubloman said:
So "Datatek" you are saying that the fault may still be the door latch and the microswitch?

Never having stripped out the door latch mech I understand that there are a number of types of door latches and some are more prone to fail than others?

However, it is said that if you can put in the EKA code, it is unlikely to be the door latch microswitches, but saying that I am going to investigate all areas to ensure that this is not overlooked in trying to fix this problem.

I have checked the plug and pins on the BECM and tested the continuity as well as tested the voltage and voltage drop on all 3 units, I would agree that the green dot unit has failed.

I have just got back from a remote location to remove the possible interference from the local issues and I still get the same issues as explained in my previous reply. This would suggest that another issue exists and it might be

The door latch (Will strip the door down tomorrow)
The RF Receiver (Need a filter)

Could it be anything else?

Thanks
Dave

In my project car, frequently it would fail to respond to the FOB, after unlocking and re-locking with the key it would again unlock from the FOB. The latch mechanism was full of crud, I washed it out and it's been fine since. so certainly the latch mechanism can cause failure to respond to the FOB.

P38 RF Receiver to BECM

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