Interesting remote locking system problem (and fix) on 94 850 wagon..

One day, I noticed that the tailgate didn't lock when I locked the rest of the doors, via remote, or key. So, I locked the tailgate with my key.

Some time later, I noticed that the remote was NOT locking the doors. I could unlock, but I had to lock it via the driver's door key, which also locked all the other doors (except the tailgate). The spare remote exhibited the same behavior, so the problem was in the car. If I used the key in the driver's door, every other door except the tailgate would lock and unlock with it.

Some initial troubleshooting revealed that, if the tailgagte was manually unlocked, then the remote would both lock, and unlock the car.

I pulled the tailgate latch assy, and noticed that the seam of the plastic motor housing was split open along the plunger side. (arrows in this photo:

I wish I had remembered to phoograph the innards, but the way is worksis that the motor (in the left side) via reductrion gears, drives acoarse pitch that runs up the middle of the plunger. The screw engages a sliding block that travels between the plungerlegs, and carries it up, or down via spring loaded detents. Itreleases it's grip on the plunger at the end of it's travel in eitherdirection, so the key lock is free to move the plunger as well. At the bottom of it's travel (unlocked), the plunger activates a switch, that signals to the central locking relay that it's locked. When it's up, an "unlocked" signal lead is grounded instead..

The casing was split along the plunger side, apparently keeping it from actuating the switch properly. When unlocked, it was still signalling the lock relay (which contains some logic) that the rear door was locked, while the other doors were grounding the "unlocked" signal. Receiving both "locked" and "unlocked" signals prevented the locking relay from responding to the input from the remote receiver.

When the tailgate was unlocked, the relay still received mixed signals in the opposite direction, but somehow, this didn't prevent it from operating.

I tried gluing the housing with cyanoacrylic cement, but it split open again on the first cycling of the remote. So, I re-glued it and reinforced it with shortened staples sunk into the plastic with a soldering iron, then secured with some more glue"

I think that the motor had a bit of overrun, and when the drive block ran into the stop, the remaining torque worked to split the casing open.

It works fine now. And, I've finally removed the loose tailgate liner so I can repair the clip anchor holes.

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