1. Check the Power Door Lock Actuators:
* Accessibility: These are located inside each door. You'll need to remove the interior door panel to access them. There are many online guides showing how to remove door panels for your specific year and model.
* Testing: With the door panel off, you can visually inspect the actuator for any obvious damage (broken parts, wires disconnected). You can also try manually operating the actuator rod (using a small flathead screwdriver if necessary) to see if it moves freely. If it's not moving, the actuator may be faulty and need replacement. This is the most likely culprit if *all* doors are affected.
2. Inspect Wiring and Connections:
* Door Harness: Examine the wiring harness that connects to each door lock actuator. Look for any broken, frayed, or corroded wires. Pay close attention to the areas where the wiring enters the door, as these are prone to wear and tear.
* Body Control Module (BCM): This module controls many electrical functions, including the door locks. While less likely to cause complete failure of *all* doors simultaneously, a faulty BCM is possible. However, diagnosing this requires more advanced diagnostics.
* Ground Connections: Poor ground connections can cause intermittent or complete electrical failures. Check the ground points for the door lock system (often located on the chassis or body near the doors). Clean and tighten any loose or corroded ground connections.
3. Check the Door Lock Switch:
* The switch itself could be faulty, especially if it's a mechanical switch (as opposed to a fully electronic push button). See if you can use the key fob to lock/unlock the doors; If the key fob works, the problem is not related to the BCM.
4. Advanced Troubleshooting (Requires Diagnostic Tools):
* OBD-II Scanner: While unlikely to directly show a problem with the door locks, a scanner might reveal related error codes that point towards a more systemic issue (like BCM failure).
* Digital Voltmeter: A multimeter can help you test the voltage and continuity of the wiring and actuators, pinpointing the exact location of the problem.
Important Considerations:
* All Doors Affected: The fact that *all* doors are affected strongly suggests a problem with the power supply (wiring, BCM), or a common component like the main control circuit itself.
Before you begin any repairs:
* Disconnect the negative battery terminal to prevent accidental short circuits.
* Consult a repair manual: A repair manual specific to your 2004 Dodge Ram 1500 will provide detailed diagrams and instructions for accessing components and troubleshooting the system. You can find these online or at auto parts stores.
If you're not comfortable working with automotive electrical systems, it's best to take your vehicle to a qualified mechanic for diagnosis and repair. The cost of replacing several actuators could exceed the cost of professional diagnosis.
