central locking buttons will lock but not unlock doors

[brownie]

The central locking button on both the driver and the passenger front doors of my 2002 XC70 will lock but not unlock the doors and tailgate, unless the driver’s door is open. Then it sometimes unlocks, sometimes not. The remote unlocks everything just fine, and, the key itself, used manually, will unlock everything.

Since all the door locks/switches function properly using the remote, I’m thinking the problem is with the central locking module on the driver’s door, but that’s just a guess and assumes that the central locking button on the passenger door requires that the central locking module in the driver’s door is functioning, which may or may not be true. Anyone have any thoughts?

Thanks

[brownie]

I found the culprit. I was on the verge of going to the dealer, but I thought I'd try one more thing: I'd swapped the four unlocking relays for others that weren't causing problems and that didn't help, but this time I bought 4 brand new ones and swapped them in, one at a time. Turned out that the tailgate unlocking relay was causing the problem. Being curious, I swapped the demonstrably bad relay for the one on the rear windshield wiper circuit, and,surprisingly, it worked fine there. I don't know why it would work on one circuit and not the other, but, for now, the problem is solved.