The first place to start would be to have a qualified repair shop hook up a factory or professional scan tool an check for DTC'S - diagnostic trouble codes stored in the BCM - body control module .
The body control module (BCM) performs multiple body control functions. The BCM can control devices directly connected to its outputs based on input information. The BCM evaluates this information and controls certain body control systems by commanding outputs on or off. The BCM control inputs can be:
• Sensors and switches that are directly connected to the BCM
• Class 2 serial data received from other control modules connected to the class 2 serial data link
The BCM is also capable of controlling other vehicle systems that are not directly wired to the BCM. The BCM does this by sending specific messages on the class 2 serial data link. The control module capable of performing the required function will respond to the BCM message.
The BCM controls these functions:
• Audible warnings--Refer to Audible Warnings Description and Operation in Instrument Panel, Gages and Console.
• Automatic door locks--Refer to Power Door Locks Description and Operation in Doors.
• Automatic headlamp control--Refer to Exterior Lighting Systems Description and Operation in Lighting Systems.
• Interior lighting--Refer to Interior Lighting Systems Description and Operation in Lighting Systems.
• Keyless entry (AUO option)--Refer to Keyless Entry System Description and Operation in Keyless Entry.
• Passlock theft deterrent--Refer to Vehicle Theft Deterrent (VTD) Description and Operation in Theft Deterrent.
• Retained accessory power (RAP)--Refer to Retained Accessory Power (RAP) Description and Operation .
Then if no DTC'S , pick one of the systems messing up . Test electrical circuit , using a wiring diagram an a DMM- digital multi-meter . Watch this video , not same model or make ,watch how this professional tech diagnose's
Chrysler Pacifica TIPM Electrical Problems