1. Check the Fuses:
* Locate the fuse box: Your Expedition likely has multiple fuse boxes – one under the hood and another inside the passenger compartment (often under the dashboard). Consult your owner's manual to locate the correct fuse box and identify the fuse(s) related to the power door locks. There might be a dedicated fuse for the rear passenger door, or a general power lock fuse.
* Inspect the fuses: Carefully check the fuses for any signs of blowing (a broken filament or a melted appearance). Replace any blown fuses with fuses of the same amperage rating. If the fuse blows immediately after replacement, you have a short circuit somewhere in the system (see troubleshooting steps below).
2. Inspect the Door Lock Actuator:
* Access the actuator: This usually involves removing the interior door panel. You'll need trim removal tools to avoid scratching the panel. There are many online tutorials specifically for 2001 Ford Expedition door panel removal; search YouTube for "2001 Ford Expedition rear passenger door panel removal".
* Locate the actuator: Once the panel is removed, you'll see the door lock actuator. It's usually a small electric motor with linkages connected to the lock mechanism.
* Visual inspection: Check the actuator for any obvious damage, loose wiring, or broken parts.
* Testing the actuator: With the door panel off, you can try applying 12V directly to the actuator's wires (using a test light or multimeter to identify the correct polarity – be very careful not to short-circuit anything). If the actuator doesn't move, it's likely faulty and needs replacement.
3. Check the Wiring:
* Inspect the wiring harness: Carefully examine the wiring harness leading to the actuator for any signs of damage, fraying, or broken wires. Pay close attention to the area where the harness enters and exits the door, as this is a common point of wear.
* Continuity test (advanced): If you have a multimeter, you can test the continuity of the wires from the actuator to the main wiring harness. This will help determine if there's a break in the wiring.
4. Check the Door Lock Switch:
* Test the switch: With the door panel off, check the functionality of the door lock switch itself. You might be able to use a multimeter to test if it's sending a signal when pressed.
* Replace the switch (if needed): If the switch is faulty, it will need to be replaced.
5. Check the Central Locking Module (Body Control Module):
* This is a less likely culprit since other doors work: The central locking module controls all the power door locks. If other functions controlled by the BCM are also malfunctioning, it might be the source of the problem, but this is less probable given your description. Diagnosing and repairing the BCM is significantly more complex and usually requires professional attention.
Replacement Parts:
You'll likely need to replace the door lock actuator if it's faulty. You can find these online from auto parts retailers like AutoZone, Advance Auto Parts, or Amazon. Make sure to specify the year, make, and model of your Expedition when ordering.
Important Considerations:
* Safety First: Disconnect the negative battery terminal before working on the electrical system.
* Professional Help: If you're not comfortable working on car electrical systems, it's best to take your Expedition to a qualified mechanic.
* Online Resources: YouTube is a great resource for finding visual guides on removing door panels and replacing door lock actuators on 2001 Ford Expeditions. Search for videos specific to your vehicle.
By systematically checking these components, you should be able to isolate the problem and repair the rear passenger power door lock. Remember to be patient and methodical in your troubleshooting.
