Possible Causes:
* Faulty Door Lock Actuator(s): The most common culprit. The actuator is the motor inside each door that moves the locking mechanism. One or more could be failing intermittently, explaining why it sometimes works. You might hear a clicking sound from a faulty actuator when you try to lock/unlock.
* Wiring Problems: Worn, frayed, or corroded wiring in the door harness (the wires connecting the doors to the car's electrical system) is a frequent problem, especially in older vehicles. Movement of the doors can aggravate this. This can cause intermittent operation.
* Body Control Module (BCM) Issues: The BCM is the car's central computer that controls many functions, including power locks. A malfunctioning BCM can lead to erratic behavior in various systems. This is less likely if the remote works *sometimes*.
* Power Lock Switch: While less likely since the remote works, the switch itself inside the car could be faulty.
* Grounding Problem: A poor electrical ground connection somewhere in the system can cause intermittent operation.
Troubleshooting Steps:
1. Check All Door Locks: Do *all* the doors exhibit the problem? If only some doors are affected, it strongly points to a problem with the actuator(s) or wiring in those specific doors.
2. Listen Carefully: When you try to lock/unlock, listen carefully at each door. Do you hear any clicking sounds from inside the door? A clicking sound usually indicates a failing actuator.
3. Inspect Wiring: Carefully inspect the wiring harnesses in the door jambs (where the doors connect to the car body). Look for any broken, frayed, or corroded wires. Pay special attention to the areas where the wires bend and flex as the door opens and closes.
4. Test the Power Lock Switch: If possible, try bypassing the interior switch and using a test light or multimeter to see if power is reaching the actuators directly from the BCM. This requires some electrical knowledge and safety precautions (disconnect the battery negative terminal).
5. Check Grounds: Locate the ground points for the power lock system (usually found on the chassis) and clean them with a wire brush. A poor ground can cause all sorts of electrical gremlins.
6. Professional Diagnosis: If you're not comfortable with electrical work, it's best to take the vehicle to a qualified mechanic or auto electrician. They have the tools and expertise to properly diagnose the problem, which could involve checking the BCM for fault codes. A scan tool might reveal clues about the issue.
Important Note: Before attempting any electrical work, always disconnect the negative terminal of the battery to avoid short circuits and potential damage to the vehicle's electrical system.
