P38A Central locking query

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Flossie

Flossie

Well-Known Member
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Location
Shropshire
I'm sure , fairly sure anyway, that I had this issue before, posted it somewhere on this site and @Datatek answered, seem to recall it was probably a sticky latch micro switch. Spent over an hour searching for my post on 'what have you done on your RR today' and cant find it.
im not even sure the issue i had back then is the same as the issue i have now.
went to lock her off the remote, led flashes but no locking, went back to it a while later with the spare fob and same thing. Put the key in the lock and it locked and unlocked fine. Tried the fobs again and everything is back to normal.
Sticky micro switch?
 
Probably time to do the latch microswitch testing. Do each test a couple of times, in case the microswitch actuation is intermittent.
 

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  • P38 Door Latch Tests.pdf
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pwood999 said:
Probably time to do the latch microswitch testing. Do each test a couple of times, in case the microswitch actuation is intermittent.
Click to expand...
Just went to download that and my phone is asking if I want to download again. I remember now doing those tests on a mates 38 with a dead door,maybe 2 yrs ago, that ended up being 2 broken wires from the A post to the becm under the sill step cover thing. Marty helped with that one over on p38 pub.
 
If you have a Nanocom, you can use the BECM Inputs menu to show the microswitches. That will prove the latch to outstation , as well as the outstation to BECM. Then if something isn't working, take the doorcard off & do the continuity checks.

The door switches should show 12V normally, and GND when you do anything with the latch. Keyswitch should toggle on both locking & unlocking. CDL will show locked or unlocked. Door ajar is what it says !!

1725102915256.png
 
pwood999 said:
If you have a Nanocom, you can use the BECM Inputs menu to show the microswitches. That will prove the latch to outstation , as well as the outstation to BECM. Then if something isn't working, take the doorcard off & do the continuity checks.

The door switches should show 12V normally, and GND when you do anything with the latch. Keyswitch should toggle on both locking & unlocking. CDL will show locked or unlocked. Door ajar is what it says !!

View attachment 324906
Click to expand...
Well, I'll go to the bottom of my stairs!
Yes, got nano but not tech savvy and I don't think I've seen that menu before.Dont have to get it out very often though as my 2001 td is proving quite reliable. Used it to set timing modulation and diagnose a faulty pot on a blend motor and that's it really. Nearly everything I've had to do has been mechanical stuff and a valve block rebuild.
Might have a play later if I get done, what I'm currently doing, early enough.
Thanks.
 
Def try the Nanocom then. Plug it in, but leave ignition off.

Then navigate menus to P38 / EDC / Right Arrow Twice / BECM / Inputs / Door-Locking /

1st screen shows front door ajar switches.
2nd screen shows rear doors, key switch & CDL (Central Door Locking).
3rd screen shows bonnet & tailgate.

Like this:
 
Last edited:
Flossie said:
I'm sure , fairly sure anyway, that I had this issue before, posted it somewhere on this site and @Datatek answered, seem to recall it was probably a sticky latch micro switch. Spent over an hour searching for my post on 'what have you done on your RR today' and cant find it.
im not even sure the issue i had back then is the same as the issue i have now.
went to lock her off the remote, led flashes but no locking, went back to it a while later with the spare fob and same thing. Put the key in the lock and it locked and unlocked fine. Tried the fobs again and everything is back to normal.
Sticky micro switch?
Click to expand...
Sticky/ failing micro switch is most likely. Today, mine thinks the drivers door is open all the time, strangely the suspension seems to be working.
 
I've played around with it for an hour and I can't get it to 'fail' again, typical.
I did notice maybe a 1 sec delay on the drivers door compared to the passenger door switching from 12v to GND very rarely though, maybe 3 times in 30 toggles. If it did it , it immediately wouldn't do it again with further toggling.
 
The delay is probably the delays in the BECM receiving & processing the data. Although the two outstations are on separate data busses, the BECM code can only do one thing at a time !!
 
Like me then...
The car is only locked and unlocked via the fob once a week, when we go shopping. Its never locked when home. I wonder if I should lock it more if that would help the micro switches stay free, if indeed they are sticky.
 
Flossie said:
Like me then...
The car is only locked and unlocked via the fob once a week, when we go shopping. Its never locked when home. I wonder if I should lock it more if that would help the micro switches stay free, if indeed they are sticky.
Click to expand...
Burnt contacts in a micro switch result in an initially high resistance contact which can delay the switch being recognised
 
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