Owner's Problem Description
The owner reported that the right daytime running light is out, the cruise control is not functioning, and the power locks do not engage when the car is put in gear. These issues appeared suddenly, and previous repairs were not mentioned. After some troubleshooting, engaging the park brake temporarily resolved the issue, leading to questions about the underlying cause and the relevant circuits involved.
Professional Technical Analysis
The 2007 Saturn Aura is equipped with a range of electronic systems that are interconnected. Given the reported symptoms, it is likely that the issues stem from a fault in the gear shift interlock system, which may not be correctly informing the Body Control Module (BCM) about the vehicle's gear position. This can cause the power locks to fail to engage when the vehicle is in gear, as they are designed to operate only when the vehicle is in 'Park'. Additionally, the cruise control may be inhibited under similar circumstances, as it requires the vehicle to be in a specific gear range to function properly. The daytime running light issue could be related to the BCM as well, which controls various lighting functions. A thorough check of the park brake switch is essential, as it plays a key role in the gear position detection system. If the switch is faulty, it may incorrectly signal that the vehicle is in 'Park', leading to the described behaviors. This vehicle's electrical system typically operates at 12-14V, and proper voltage levels must be verified to ensure all systems are functioning correctly. Engaging the park brake and observing changes in system behavior indicates a possible fault in the switch itself or its connections. Current condition assessment shows intermittent functionality, which raises safety concerns.
Possible Causes
Most common causes (ordered by frequency):
- Park Brake Switch Failure: The switch in the park brake assembly may be malfunctioning, causing the BCM to improperly detect the vehicle's gear position. This could lead to the cruise control and power locks failing to engage when the vehicle is in gear. The switch should show continuity when the brake is engaged and open when released. - Issues resolved when park brake is engaged, indicating possible switch failure; continuity testing required.
- Gear Shift Interlock Issue: A malfunction in the gear shift interlock mechanism could cause the BCM to misinterpret the position, affecting both the locking mechanism and cruise control functionality. Inspection of the gear shift assembly is necessary. - Cruise control and locks engage when park brake is applied, suggesting interlock dysfunction; visual inspection required.
- BCM Malfunction: The Body Control Module itself may be experiencing faults, leading to erratic behavior of various electrical components including lights, locks, and cruise control. Diagnostic scanning may reveal fault codes related to BCM. - Inconsistent operation of electrical components; diagnostic scan necessary to identify BCM-related fault codes.
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 - Perform Initial OBD-II Scan: Use a professional OBD-II scanner or GeekOBD APP to retrieve any stored fault codes. This step is vital to identify any underlying electrical issues that may be affecting the BCM or related systems. Pay attention to any codes pointing toward the BCM or gear shift interlock system.
- STEP 2 - Inspect Park Brake Switch: Visually inspect the park brake switch for signs of wear or damage. Perform a continuity test to ensure it operates correctly when engaged and released. If the switch fails to show continuity when engaged, it may need replacement.
- STEP 3 - Evaluate Gear Shift Interlock: Check the gear shift mechanism for proper operation. Ensure that the interlock is functioning correctly and verify that it communicates properly with the BCM. Look for any signs of wear or damage in the linkage.
- STEP 4 - BCM Functionality Testing: If issues persist, conduct a thorough diagnostic scan of the BCM using the GeekOBD APP to check for fault codes. Follow manufacturer recommendations to reset or reprogram the BCM if necessary.
