Owner's Problem Description
The owner of a 1991 Chrysler Fifth Avenue with a 3.3L engine and 120,000 miles reports that all four power door locks malfunction simultaneously. The locks engage automatically when the vehicle reaches 15 mph. No aftermarket or factory alarms are installed. The owner has attempted removing the fuse, which disables the locks, but the automatic locking feature persists. Seeking guidance on diagnosing the actuators and their locations.
Professional Technical Analysis
The 1991 Chrysler Fifth Avenue, equipped with a 3.3L engine and approximately 120,000 miles, presents a unique issue with its power door lock system. The owner reports that all four locks engage automatically at 15 mph, indicating a potential fault in the Body Control Module (BCM) or the door lock relay system. Diagnostics suggest that the actuators may be shorted, as indicated by the simultaneous malfunction. Each door is equipped with an actuator, and the simultaneous failure points towards an electrical issue rather than mechanical. The BCM controls the locking system, including the auto-lock feature that activates above a certain speed, typically around 15 mph. Further investigation is needed to assess the integrity of the wiring harness and the operation of the relay. Additionally, the presence of a proper ground and power supply to the actuators must be confirmed, as failure in these areas could lead to the described symptoms. Given the vehicle's age and mileage, wear and electrical corrosion are common issues that could affect system performance, especially at high humidity or extreme temperatures. A thorough inspection of the BCM and its connections, along with testing of the lock actuators, is critical to pinpointing the root cause of the problem.
Possible Causes
Most common causes (ordered by frequency):
- Body Control Module (BCM) Malfunction: The BCM controls the power door locks and automatic locking feature. A malfunction or short circuit within the BCM can cause all locks to engage simultaneously. This can be verified by checking for fault codes in the BCM using a professional scan tool. If the BCM is found defective, replacement with OEM P/N 4600568AB is recommended, which typically costs around $200-$300. - Checking for stored fault codes in BCM shows potential actuator control issues. The automatic lock feature activates consistently at 15 mph, indicating BCM involvement.
- Door Lock Actuator Failure: Each door is outfitted with an actuator that can fail due to wear or electrical failure. If multiple actuators are shorted or have failed simultaneously, it could lead to the symptoms described. Testing each actuator's resistance (normal range 20-60 ohms) can help identify faulty units. - Physical inspection of actuators reveals signs of wear or corrosion. Resistance testing shows readings outside the normal range for some actuators.
- Wiring Harness Issues: The wiring harness connecting the BCM to the door lock actuators may have developed corrosion or damage, leading to intermittent or simultaneous failures. Inspecting the harness for frays or breaks and testing continuity can help diagnose this issue. - Visual inspection of wiring harness shows signs of fraying or oxidation. Continuity tests reveal inconsistencies in the connections.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Scan with GeekOBD APP: Begin by using the GeekOBD APP to scan for diagnostic trouble codes (DTCs) in the BCM. This will provide valuable insight into any stored codes related to the door lock system, which can guide the next steps in diagnosis.
- STEP 2 - Inspect Door Lock Actuators: Remove the door panels to access the door lock actuators. Inspect each actuator for physical damage and test their resistance. Normal resistance should be between 20-60 ohms. Document any actuators that fall outside this range for further testing or replacement.
- STEP 3 - Check Wiring Harness: Inspect the wiring harness for signs of wear, corrosion, or damage. Utilize a multimeter to test for continuity throughout the harness. Any breaks or high resistance in the connections could indicate faulty wiring that needs repair or replacement.
- STEP 4 - Test BCM Functionality: If no issues are found with the actuators or wiring, test the BCM functionality. This may involve replacing the BCM temporarily with a known good unit or using a professional scan tool to perform specific BCM tests.
