P38A BBUS going off randomly

Hi All,

I've been having lots of electrical headaches with my P38, mostly relating to the starter operating itself and the battery going flat.

Wrt the battery going flat, I've disconnected the RF receiver wire and had been running an experiment to monitor the battery voltage. After 4 weeks, it had lost only half a volt so I think this probably is the main cause of my flat battery - my OH's father has made me a remote switch for the rf receiver which I am all set to fit.
Unfortunately, my battery monitoring experiment had to be terminated a couple of weeks ago when the alarm went off in the middle of the night for no apparent reason - the car wasn't even locked. Emergency solution was to pull the battery terminal and go back to bed.

I reconnected the battery yesterday and even managed to get the keyfob to synch immediately which almost never happens! Having again left the car unlocked, the alarm went off again for no reason about an hour later - it seems to be the BBUS module behind the fuse box. And blimey, it is loud!

No indicators were flashing, no messages were displayed on the message centre and nothing I could do with the key or keyfob would shut it off - I had to disconnect the battery.

Now, given that I understand this to be a self contained unit - I'm guessing that perhaps the internal batteries might be knackered given that disconnecting the main battery actually shuts it up.

I seem to remember that my OH's Audi had a similar problem when the battery died in her alarm sounder. Do P38's do the same thing, or is it likely to just be a knackered BBUS unit? Bit suprised not to find more information on it if that was the case as they're all getting long in the tooth now. Can I just disconnect it?

Any other diagnosis I can perform on it?

I'm starting to think this P38's days are numbered...

If you have diag make sure that BBUS sounder is selected in BECM. The battery must be disconnected according to the instructions in RAVE if you have a BBUS sounder.

Hi Wammers,

No diagnostics unfortunately other than an EAS Kicker. Don't they all have BBUS sounders?

The battery has been disconnected/gone flat so many times on this during my ownership - I've never had this issue before though.

Hmm, looking in Rave, it states the BBUS will sound if the vehicle battery or the BBUS is disconnected unless the proper disconnect procedures are followed. That's never happened to me before (ie gone off when I disconnect the battery) implying that it's not working properly at the very least,

Rick thinks it may be the becm again. Happy days.

Guy

kooky_guy said:

Hi Wammers,

No diagnostics unfortunately other than an EAS Kicker. Don't they all have BBUS sounders?

The battery has been disconnected/gone flat so many times on this during my ownership - I've never had this issue before though.

Hmm, looking in Rave, it states the BBUS will sound if the vehicle battery or the BBUS is disconnected unless the proper disconnect procedures are followed. That's never happened to me before (ie gone off when I disconnect the battery) implying that it's not working properly at the very least,

Rick thinks it may be the becm again. Happy days.

Guy

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Not all have BBUS sounders. Klaxon or BBUS can be set in BECM. BBUS unit is designed to go off if a battery lead is cut. If it does not go off when you disconnect the battery without using the approved method odds on batteries are duff. Are you superlocking the car, could be a fault on the passive detector.

I'll have to try and find the becm config printout that Rick produced for me when he was repairing it - that will probably tell me.

I'm pretty sure superlocking has never worked on this vehicle. At least it doesn't do anything extra when you double click the lock button. It's always possible to open the doors from the inside when locked.

In any case, both times the alarm went off, the car was unlocked. It's back to having it's battery disconnected again now as I can't trust it.

kooky_guy said:

I'll have to try and find the becm config printout that Rick produced for me when he was repairing it - that will probably tell me.

I'm pretty sure superlocking has never worked on this vehicle. At least it doesn't do anything extra when you double click the lock button. It's always possible to open the doors from the inside when locked.

In any case, both times the alarm went off, the car was unlocked. It's back to having it's battery disconnected again now as I can't trust it.

Click to expand...

Just disconnect the BBUS unit.

Simple as that?

kooky_guy said:

Simple as that?

Click to expand...

If it's not connected it can't sound can it. If there is nothing else apparent other than the sounder going off, it is at least a stop gap.

wammers said:

If it's not connected it can't sound can it. If there is nothing else apparent other than the sounder going off, it is at least a stop gap.

Click to expand...

I guess so but since I'm still not able to use it for various other reasons I'd rather try and get it fixed properly.
Think we're going to go for a replacement becm, given the ongoing problems with the starter running itself as well.

kooky_guy said:

I guess so but since I'm still not able to use it for various other reasons I'd rather try and get it fixed properly.
Think we're going to go for a replacement becm, given the ongoing problems with the starter running itself as well.

Click to expand...

Only reason starter circuit goes through BECM is because BECM interfaces fuel cut off and security code before allowing ignition switch to ground starter relay pull with key in position three. Sounds like ground leak somewhere. Maybe fuse box.

Well it's already had a fuse box. And a Becm repair. Bit frustrated with it to be honest.