My 99 GP passenger side power door lock failed to lock intermittently. It would always unlock but would sometimes not lock. The drivers door always worked ok. The BCM (Body Control Module) controls this function so I tested the door lock circuit at the connector (C1 - pins A, B, C) on the BCM. I could get the door to lock/unlock correctly when applying power to the appropriate pins.

+12V to pin C, GND to pin B will lock the passenger door; GND to pin C, +12V to pin B will unlock that door.

+12V to pin C, GND to pin A will lock the drivers door; GND to pin C, +12V to pin A will unlock that door.

Since that test proved the door lock motor and wiring to that motor must be ok, I went inside the BCM. The locking circuit is controlled with 3 relays inside the BCM. I replaced all three of these relays even though only one of them was bad. The relays originally used were Siemens brand. I could not find them so found an alternate that had the same pin pattern and ratings. It was an Omron G5LE-14-DC12 and can be purchased from Allied Electronics for $1.06 each. I desoldered the old relays, soldered in the new relays and my passenger side power door lock has worked ever since.