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Central Locking Problems 900

posted by  sunapeelakers on  Thu Nov 12 15:43 CST 2020
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Hey guys - I've gotten a ton of help here and I really appreciate this site!

I have had a pretty significant issue with central locking recently that has been aggravating to think about. As I was driving down the road, all my doors randomly locked. I parked the car when I got home, got out, and locked my door - only the drivers door locked. I noticed when I locked the door, the instrument panel lights as well as the parking lights would flash... Not making a ton of sense.

I pulled the central locking relay (1993 945T), and it has the odd-shaped Hella relay. I pulled the relay open, and noticed it was visibly burned up on the pcb solder points. I attempted to resolder them, but it did not work - one of the metal strips was broken and no longer attached to the board.

No big deal - I could grab one at the junk yard and fix the issue. Well, I went to the junk yard, and hit up the 740 wagon I have been pimping parts off of for a while, and sure enough, it had the relay - EXCEPT - the relay was not the Hella relay, it was just a rectangular relay, but had the same pins in the same pattern as the Hella from my car did. I grabbed it anyways, and put it in my car, and it didnt work. Doors still do not lock with the drivers door.

Also, possibly related, the tailgate would not unlock after this happened. So, if I put my key in the cylinder, it would turn to the left as if you were locking it, but WOULD NOT turn to the right to unlock, no matter what I did. I ended up breaking the lock cylinder by trying too hard to turn the key to the right. I took the tailgate panel off, and was able to rotate the motor in the tailgate so it is currently unlocked and able to be opened by the handle. Now, if I put the key in the tailgate cylinder, there is no tension on it, it spins freely from left to right, and doesnt do anything - possibly unhooked from the latches inside the tailgate?

Would the motor in the tailgate have caused the relay to fry itself?
I have checked fuse #2 and it is in tact - my headlights and hazards both work fine.

Any help would be great!








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    Central Locking Problems 900

    posted by  sunapeelakers on  Mon Dec 21 17:07 CST 2020
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    Ok so I finally got around to replacing the tailgate actuator, and it does lock and unlock now, however only the drivers door and tailgate lock and unlock. Is there a trick to syncing the rest of the doors?








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      Central Locking Problems 900

      posted by  Nahtanha on  Mon Dec 21 17:57 CST 2020
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      last visit: Tue May 20 10:10 CST 2014
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      Opening up the main switch pack and cleaning. Should be a main wiring harness plug that you could clean. These switches do get old and dirty inside. Find all you accessible ground wiring and clean / tighten them.








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        Central Locking Problems 900

        posted by  sunapeelakers on  Mon Dec 21 19:22 CST 2020
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        main switch pack in the drivers door? Idk... its triggering the relay so I feel like the fault is probably going to be between the relay and the other doors. just weird that three doors would simultaneously crap out. I cant imagine thats the case. I thought there was a process to reset it and get them all synced again.








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    Central Locking Problems 900

    posted by  machine man on  Sun Nov 29 21:04 CST 2020
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    last visit: Wed Oct 22 15:40 CST 2014
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    Hi,

    I don’t know anything about these cars as I’m a 240 man.

    What I will say is, it seems that you have noticed the problem right after getting in the car and driving someplace.
    This means you had just used the door key in the door lock of the drivers door.
    You then got out and more weird things started to happen, right?

    I think you have a broken switch in the drivers door.
    These can be a problem on the 240’s, especially with the wiring around the switch on into the switch inside the door. Removal of the inner door panel is the only entry point.
    On the 240 tailgates they run the harness through the hinges and that breaks down the wires.
    So you might even consider the harness in the hinges area of the drivers door.
    I think the 900’s do not route the tailgate harness through hinges but loop in it under the top of the door, to the top of the roof?

    The 240’s had wiring harness issue in the early years, say the mid eighties, of just plain getting rotting insulation.
    I don’t know if the factory ever got them foolproof up to the end of the 240 production.
    Why wouldn’t Volvo use nearly their same vendors but changed design, later?

    I’m just going to say that the 900’s can develop these problem with age and use.
    A lot of issues depend on under what environments the cars were used in?
    It has been long enough for some type issue to develop.
    I always point my self in the direction of “What can the human hand touch and wear out? Breaking is another word.
    The drivers door and a tailgate are probably the most used and abused door on any car!
    The tailgates get dropped, especially, if the lifts are weak in summer and they get worse when it’s colder!
    Lots of plastic clips hold the locking rods tight.

    It is a place to at least to start looking!

    Phil








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      Central Locking Problems 900

      posted by  Will740turbo on  Tue Dec 15 12:17 CST 2020
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      last visit: Wed Oct 22 16:09 CST 2014
      [RELATED]

      I think this is the right track.

      I had the rotting wiring harness (1982-1988, I think) on my 84, under the hood but also at the reverse light switch, the door lock switches, and a few other places.

      I had a pair of wires rub through a quarter inch from the switch (mounted on the lock cylinder) and turning the key started my locks doing a fun little dance of lock, lock, unlock, lock, unlocked open me! haha too slow locked again... when I was trying to open my door. The wires were shorting intermittently, and thumping the door stopped it long enough to open it.

      It could be entirely because of the tailgate lock switch and solenoid, so I would start by disconnecting it in the tailgate and inspecting the wiring at the hinges or at one of the body connectors in the driver-side door wiring channel. This basically runs the entire length of the interior from firewall to trunk along the indoors side of the car's edge.

      My guess is: Driver's or other door lock is shorted to ground or from wire to wire somewhere - probably driver's lock, but maybe tailgate. That got the locking relay stuck on, which (along with age) burned it up. The fuse and relay socket may be damaged too. Find what circuit has the short, fix it (run a new wire, don't try to find the exact spot of shorting), then deal with the relay, socket, and fuse.

      Good luck!








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        Central Locking Problems 900

        posted by  sunapeelakers on  Fri Jan 1 08:41 CST 2021
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        Hey Will,

        I'm also inclined to believe this is an issue with the relay socket where the central locking relay attaches to the fuse panel. Looking at it from the top, with the relay out, it doesnt seem like there are any visible problems. How do you remove the fuse tray entirely to get to the bottom of the tray?







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