"Thunk" sound from back seat area when locking doors

[MadeInJapan]

Speakers or further back (like I suspected earlier). Not hard to see the wiring to those speakers from withing the trunk area (if this is truly the source of your sound). Take a look to make sure something isn't shorting the lead speaker wires (the one on the cone(s) somehow to the car's body.

[StarmanDXE]

100% sure it is the speakers. You can see the cones move and I even held my finger to it and felt it move (like the cone was going full-swing with the +12V [or whatever] the central locks use to initiate...) Will have to check for any unintentional grounding.

[StarmanDXE]

More symptoms! (And things get weirder...)

So, I noticed a few days back that the rear-driver's side door wasn't locked after all of the doors had been locked with the remote. This seems to be becoming an intermittent problem. It happened to me again today. But it only seems to occur if the doors are locked when the car is running. (And only sometimes.) If the lock stays open, then it won't follow the rest of the locks (no matter what you do) until you manually lock it.

Here's the really strange part: if that door doesn't lock with the rest (from the inside) and I reach back and lock it, it will cause the rear speakers to "thunk"...

I still have yet to look at any wiring diagrams or poke around much (but now I assume I will need to pull the door apart, too... ), but anyone happen to have any ideas?

Thanks!

[VCA]

More symptoms! (And things get weirder...)

So, I noticed a few days back that the rear-driver's side door wasn't locked after all of the doors had been locked with the remote. This seems to be becoming an intermittent problem. It happened to me again today. But it only seems to occur if the doors are locked when the car is running. (And only sometimes.) If the lock stays open, then it won't follow the rest of the locks (no matter what you do) until you manually lock it.

Here's the really strange part: if that door doesn't lock with the rest (from the inside) and I reach back and lock it, it will cause the rear speakers to "thunk"...

I still have yet to look at any wiring diagrams or poke around much (but now I assume I will need to pull the door apart, too... ), but anyone happen to have any ideas?

Thanks!

I'd wager it's a short in the door wiring on that particular door. There are some contacts that make/break when the lock is locked/unlocked (separate from the solenoid power to operate the power functions) that tell the REM whether a particular lock module is locked. Can you make the sound on demand when cycling that door's lock? If so, time to pull the door panel and perhaps even the door's interconnect to the B-pillar--the audio wiring doesn't go through the REM, so it's almost assuredly a wiring short.

[StarmanDXE]

Can you make the sound on demand when cycling that door's lock?

I will check. I do think it was, but I don't know if that was only when it was having the issue.

If so, time to pull the door panel and perhaps even the door's interconnect to the B-pillar--the audio wiring doesn't go through the REM, so it's almost assuredly a wiring short.

Huzzah! Mere months after fixing the locks in that darn 850, I'm having problems with my new car...

So, if the audio wiring doesn't go through the REM (what's that stand for, anyway?), any idea why it would cause speaker issues?

[VCA]

Can you make the sound on demand when cycling that door's lock?

I will check. I do think it was, but I don't know if that was only when it was having the issue.

If so, time to pull the door panel and perhaps even the door's interconnect to the B-pillar--the audio wiring doesn't go through the REM, so it's almost assuredly a wiring short.

Huzzah! Mere months after fixing the locks in that darn 850, I'm having problems with my new car...

So, if the audio wiring doesn't go through the REM (what's that stand for, anyway?), any idea why it would cause speaker issues?

The REM is the Rear Electronics Module (that box in the trunk on the LH side behind the lining with fuses and relays). The two systems don't cross physically--though central locking (obviously) is in the same door harness as the the speaker wiring--so it would be prudent to fault trace looking for short circuits. For wire colors of the central lock system, see page 86 of the wiring diagram for your car.

[Doug S]

This problem sounds like interference from the motor in the door lock.
I recently had a problem with my door lock not locking all the time and replaced the lock assembly. I didn't get noise through the speakers but I did take apart the lock assembly and there is a motor that locks/unlocks the mechanism. If there is some problem with the motor it can cause interference and this is what you may be hearing through your speakers.

[StarmanDXE]

The REM is the Rear Electronics Module (that box in the trunk on the LH side behind the lining with fuses and relays). The two systems don't cross physically--though central locking (obviously) is in the same door harness as the the speaker wiring--so it would be prudent to fault trace looking for short circuits. For wire colors of the central lock system, see page 86 of the wiring diagram for your car.

Thanks for the info. But, the monkey-wrench gets thrown in at the point where the only speakers that make the noise are the rear deck speakers, not the rear door speakers... (And it's not just the left rear deck speaker, it's both!)

This problem sounds like interference from the motor in the door lock.
I recently had a problem with my door lock not locking all the time and replaced the lock assembly. I didn't get noise through the speakers but I did take apart the lock assembly and there is a motor that locks/unlocks the mechanism. If there is some problem with the motor it can cause interference and this is what you may be hearing through your speakers.

I think this may very well be the answer. I drove around a bit tonight with the radio off. The lock still malfunctioned, but there were no popping noises from the speakers. Guess I'll be ripping that door apart and replacing the actuator... (I hope it's easier than in the 850!) That is, unless I find any obvious wiring issues in the trunk at the REM. But, I think your diagnosis of a bad motor seems more likely... Just strange that only those two speakers would make noise...

Thanks for the help guys, but I suppose it's about time I started to pull things apart

[VCA]

This problem sounds like interference from the motor in the door lock.

Brilliant! I did more checking up, and there are two points at which the central locks and the rear deck speakers cross: the rear harness and connectors 54/20 and 54/21. Turns out the rear deck speakers (16/17 and 18) are tied to the rear door (16/5 and 6) speakers via splices. Therefore, it's plausible that interference from the lock modules would affect them. They all travel through the same cable harness, so one bad rear lock module causing EM interference could, plausibly, cause this effect to both rear speakers; their point of intersection being the cargo compartment harness that ties the locks into the REM.

[StarmanDXE]

Well, if that's true, then I guess that means that the rear door speakers are making the noise, too, and I just never noticed. (I can't imagine just the rear deck speakers making the noise and not the rear door speakers. This is something I will have to check on.)

And, if this is the problem, the effect on the speakers was as if it was getting a DC voltage. Therefore I am inclined to believe that the speakers are sapping some of the power from the locking circuit and perhaps this is why the lock fails to move some of the time (i.e. not enough power). But that does not explain why the speakers only move when the radio is on...

Too much conjecture and not enough digging around. (I am usually quite guilty of that! ) I will have to start pulling stuff apart and hopefully I will find something!