Owner's Problem Description
The owner reports that the security light on their 2009 Pontiac G6 remained illuminated after a series of key cycles. Initially, the car also chimed as if warning about the seatbelt not being fastened. The driver noticed low fuel warnings briefly appearing in the driver information center (DIC). Previously, the vehicle exhibited codes U2105 and U2107, which have now changed to C0899 (device 1 low voltage) and U2105 (EMC communication). The owner is uncertain what 'Device 1' refers to.
Professional Technical Analysis
The 2009 Pontiac G6 is equipped with a robust Body Control Module (BCM) that governs various electronic systems including the security system, communication networks, and warning indicators. The presence of the security light indicates that the system has detected a fault or that the vehicle is in a theft deterrent mode, possibly due to a fault in the key fob or ignition system. The initial DTCs (Diagnostic Trouble Codes) U2105 and U2107 indicate communication issues within the vehicle's network. The change to C0899 suggests a low voltage condition affecting a specific device, likely related to the BCM or the communication lines. The 'Device 1' could refer to the BCM itself or a module connected to it that is experiencing voltage drop or communication failure. This situation may arise from poor electrical connections, a failing module, or issues in the wiring harness. Given the vehicle's age, approximately 100,000 miles, connection corrosion or wear can be a contributing factor. Safety concerns arise if the vehicle enters a no-start condition due to security system activation. It's crucial to verify the power supply to the BCM and assess the network integrity by checking voltage levels (typically 12-14V under normal operation) and continuity in communication circuits. Additionally, assessing the condition of the key fob battery and reprogramming the fob may be necessary to rule out key-related issues.
Possible Causes
Most common causes (ordered by frequency):
- Body Control Module (BCM) failure: The BCM is responsible for managing security systems and communication protocols within the vehicle. A failure in the BCM can manifest as intermittent communication issues, leading to codes U2105 and U2107. The appearance of C0899 indicates a low voltage condition that may be affecting the BCM's ability to communicate effectively, possibly due to internal component failure or external wiring issues. Voltage to the BCM should be checked to ensure it is within the range of 12-14V. - Intermittent security light, communication DTCs, low voltage warning.
- Poor electrical connections: Corrosion or loose connections at the BCM or related wiring harness can lead to voltage drops and communication failures. Given the vehicle's age, oxidized connectors may contribute to the issues observed. Voltage measurements should be taken at the BCM connector to check for proper voltage levels (12-14V) and continuity across terminals. - Visual inspection of connectors, voltage drop when wiggling wires, DTCs related to communication failures.
- Key fob or ignition switch issues: If the key fob battery is low or the ignition switch is malfunctioning, the vehicle may not recognize the key properly, causing the security light to activate. This can also lead to communication errors with the BCM. Testing the key fob battery and ensuring the ignition switch functions correctly is important. - Security light activation, no-start conditions, key fob battery voltage below specifications.
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 OBD-II Diagnostic Scan: Begin with a thorough scan using a professional OBD-II scanner or GeekOBD APP to retrieve any stored DTCs. Investigate freeze frame data for context on when the codes were set. This provides insights into the vehicle's condition during the occurrence of the faults.
- STEP 2 - Voltage and Continuity Tests: Measure the voltage at the BCM connector with the ignition on (should read 12-14V). Check for continuity between the BCM and key components, including the ignition switch and key fob. This helps identify any breaks or high resistance in the wiring.
- STEP 3 - Inspect Physical Connections: Perform a visual inspection of the BCM and related wiring harness for any signs of corrosion, loose connections, or damaged wires. Clean any corroded terminals and tighten connections to ensure reliable contact.
- STEP 4 - Key Fob and Ignition Testing: Test the key fob battery voltage (should be above 3V) and check the operation of the ignition switch. If necessary, reprogram the key fob to eliminate any key recognition issues.
