Central Locking Problem - No Trunk Lock/Unlock

Post by **larrybum** » 29 Dec 2011, 07:06

I have a '96 Volvo 850 that I bought recently. It had two fobs and 3 keys including a Valet Key which I understand will only open the doors, not trunk, nor glove compartment. The trunk will not lock/unlock when I use either the drivers key nor the remote. Everything else locks/unlocks as I would expect it to.

I can lock unlock the trunk with a key. When I do that, the doors are not affected. It seems a if the trunk is simply isolated.

I examined the lock mechanism itself on the trunk and replaced it with another known working lock from a '95 850 that I had replaced with this one (I let it overheat badly and the engine nearly seized). The lock was not the problem. I traced the wiring down the trunk arm where I thought the wiring could be scraped and shorted or some such but everything looked fine.

Does anyone have a suspect place to look? My '96 has a (forgot what you call it) double click system...to open all doors with the remote or with the driver's key, you click the remote or turn the key two times...first time, drivers' door opens, second time the rest of the doors (except for the trunk). Is it possible that the central relay is bad? This system is pretty complex to trace, but am wondering if anyone has seen a similar problem and fixed it.

Post by **Ozark Lee** » 29 Dec 2011, 07:18

I had a similar problem and the problem, along with the license plate not being illuminated, turned out to be the wiring harness that runs along the driver's side arm for the trunk. Once I tracked it down it looked like someone tried to slam the trunk on a suitcase or something. The overall loom looked fine but all of the wires were chopped inside of the loom.

They were easy to splice back together with butt splices.

...Lee

Post by **larrybum** » 19 Jan 2012, 11:59

Many thanks to Lee for his comment. I had actually taken a thorough look at the wiring running down the trunk like arm and it looked good. After his post, I took a look again. This time, I cut the webbing that covered the group of wires so that I could slide it down and see the wires themselves. Sure enough, within a foot of the exit of the wires from the trunk lid arm to the side of the trunk itself, there was a broken wire. The two heaviest wires (yellow and yellow/black) were damaged. One wire was broken, the other had the insulation broken, but the wire was ok. These wires carry the current to the lock motor in the trunk. I simply butt-spliced it and put things back together. I may have been mistaken in describing the original symptom. I could LOCK the trunk with my key at the trunk and it would cause the doors to lock. Unlocking the trunk had no effect on unlocking the doors (maybe that's the way it works anyway). After the fix, opening the doors with the remote also operated the trunk lock and locking the doors also locked the trunk.

Without Lee's suggestion, I never would have taken this second look. I had earlier viewed the wiring diagram and determined that, if either of these two wires going to the motor were broken, that was the most likely cause since all other locks and the gas cap were working as designed. Glad to have this one behind me.