* Doors won't lock or unlock automatically: This is the most obvious symptom. The power locks might work manually with the key or the interior switches, but the automatic locking/unlocking feature (when you lock with the key fob or reach a certain speed) won't function.
* Intermittent operation: Sometimes the automatic locking works, and sometimes it doesn't. This points to a relay that's failing intermittently, perhaps due to heat or corrosion.
* Other electrical issues: If the relay is failing badly, it might draw excessive current and cause problems with other electrical components. This is less common but possible. Look for blown fuses or other electrical gremlins if you suspect a major relay problem.
* Clicking sounds: You might hear clicking sounds coming from the area where the relay is located (usually in a fuse box under the hood or in the passenger compartment) when you try to lock/unlock the doors automatically. This suggests the relay is trying to engage but failing.
How to Diagnose (Beyond just symptoms):
1. Check the fuses: Before assuming it's the relay, check the related fuses in your owner's manual or under the hood fuse box. A blown fuse could prevent the relay from functioning.
2. Locate the relay: Consult your Ford Expedition's repair manual or online resources to find the exact location of the power door lock relay. It's often in a fuse box, and often labeled.
3. Visual Inspection: Once located, carefully inspect the relay for any signs of physical damage, such as burnt contacts, or unusual discoloration. However, this is often not conclusive.
4. Relay Swapping (best method): The most reliable method is to swap the power door lock relay with a relay of the same amperage and type from a different, known-good circuit (if you're comfortable doing this). If the problem follows the relay to the new circuit, the relay is faulty. If the problem stays with the door locks, the problem lies elsewhere (wiring, BCM, door actuator, etc.).
5. Use a multimeter (advanced): If you're comfortable with basic electronics, a multimeter can check the relay's continuity and coil resistance to verify it's functioning correctly according to its specifications. You'll need the relay's specifications to do this accurately.
Important Note: If you're not comfortable working with car electrical systems, it's best to take your Ford Expedition to a qualified mechanic or auto electrician. Incorrectly diagnosing or replacing parts can lead to further damage and more expensive repairs.
