* Wiring: A broken, frayed, or corroded wire in the circuit specifically dedicated to the trunk and fuel door release is the most common cause. These wires are often routed through areas prone to wear and tear (like door jambs and hinges). The wire break might be anywhere between the main power source and the actuators.
* Actuators: The motors or solenoids responsible for actuating the trunk and fuel door releases may have failed. These are small electric motors that are responsible for the mechanical movement. One or both could be burnt out or seized.
* Relay: There might be a separate relay specifically for the trunk and fuel door release. While less common, a faulty relay could prevent operation while leaving the door locks functional. Check your owner's manual or online wiring diagrams to locate a potential relay for these functions. They aren't always readily visible in the fuse box.
* Body Control Module (BCM): This is the brain that controls many electrical functions, including door locks, trunk release and fuel door release. A malfunctioning BCM could send incorrect signals or no signals at all. This is less likely given that your door locks work but is a possibility.
* Faulty Switch: The buttons you press to activate the trunk and fuel door release could be malfunctioning. A multimeter can be used to check if they send a signal when pressed.
* Hidden Fuse/Circuit Breaker: While you've checked the easily accessible fuses, there might be a less obvious fuse or even an in-line circuit breaker somewhere in the wiring harness dedicated to the trunk and fuel door releases. Consult your owner's manual or a wiring diagram to identify potential locations.
Troubleshooting Steps:
1. Wiring Inspection: Visually inspect all wiring related to the trunk and fuel door releases, looking for breaks, corrosion, or damage. Pay close attention to the wiring near the trunk and the fuel door itself, as well as the area where these wires run through the car body.
2. Relay Check (if applicable): Locate a potential relay (wiring diagrams are crucial here) and check it for continuity. Sometimes relays make clicking sounds when they are activated. If it's clicking but nothing happens, the relay might be fine, but there may be other underlying problems.
3. Actuator Testing: Try accessing the trunk and fuel door release actuators (they are typically located near the mechanism itself). You can either use a multimeter to check for power reaching the actuator (when the button is pressed), or, carefully, attempt to actuate them manually (if you have access).
4. BCM Check (Advanced): This requires a diagnostic scan tool to check for any fault codes related to the BCM. A mechanic with access to this equipment would be needed.
5. Consult a Wiring Diagram: An online wiring diagram specific to your 1999 Cadillac DeVille is indispensable for tracing the circuits related to the trunk and fuel door releases. These diagrams will show the location of relays, fuses, actuators and wire routing.
Without a wiring diagram, it's difficult to be precise about fuse locations. The fact that your door locks are working suggests the primary fuse for the locking system isn't blown. But a specialized fuse for those specific functions might exist elsewhere. A wiring diagram will show you exactly what to look for.
