Possible Causes and Fixes:
1. Fuses: Check the owner's manual for the fuse(s) related to the power door locks. A blown fuse is the easiest and cheapest fix. Replace any blown fuses with the correct amperage.
2. Door Lock Actuators: These are the small motors inside each door that actually move the locking mechanism. They can fail from wear and tear, especially if you've experienced issues with the locks in the past. Symptoms might include a specific door not locking/unlocking, or a clicking sound from the door when you try to activate the locks. Repair involves replacing the faulty actuator(s). This is usually a DIY-able repair, but requires some mechanical aptitude.
3. Central Locking Module (Body Control Module - BCM): This is the "brain" that controls all the power door locks. A faulty BCM can cause intermittent or complete failure of the system. Symptoms might be inconsistent locking behavior across multiple doors. Diagnosing a BCM issue requires advanced diagnostic tools, and replacement is usually the only solution (and can be expensive).
4. Wiring Issues: Wires can fray, break, or become disconnected due to age, wear, or rodent damage. This is particularly common in the door jambs where wires bend frequently. You'll need to visually inspect the wiring harness running to each door. Repair involves splicing or replacing damaged sections of wire.
5. Vacuum System (If Applicable): Some older cars, while less common in 1996, used a vacuum system to operate the locks. Leaks in the vacuum lines or a faulty vacuum pump would prevent proper operation. Diagnosing this requires checking vacuum lines for leaks and ensuring the vacuum pump is functioning.
6. Switch Problems: The switch in the driver's door or the key fob's remote transmitter may be malfunctioning. Try the lock switches on all doors. If some work and others don't it's probably not the BCM. If the problem only occurs with the key fob, check the battery in the remote or the remote itself might be faulty.
7. Low Battery Voltage: A weak battery can cause intermittent electrical problems, including issues with power door locks. Check the battery voltage with a multimeter.
Troubleshooting Steps:
1. Check Fuses: Always start here. It's the easiest and quickest check.
2. Test All Doors and Switches: See if the problem affects all doors, or just one or two. This will help isolate the issue.
3. Listen for Clicking Sounds: A clicking sound from a door when you try to lock it usually indicates a failing actuator.
4. Inspect Wiring: Carefully examine the wiring harness to each door, looking for damage.
5. Use a Test Light or Multimeter: If you have some electrical experience, you can use a test light or multimeter to check for power at the actuators and switches.
6. Professional Diagnosis: If you've exhausted all other options, take your car to a qualified mechanic or auto electrician for a professional diagnosis.
Important Note: Working with car electrical systems can be dangerous. If you're not comfortable working with electricity, it's best to leave the repairs to a professional. Improper repair can damage other parts of your vehicle's electrical system.
