Owner's Problem Description
The vehicle owner attempted to clear a mouse nest from the blower cage, which required removing the BCM from under the dashboard. During the process, the BCM box opened and its internal circuit fell out. After reassembling everything, the vehicle would start but immediately stall. The owner replaced the BCM, expecting it to resolve the issue, but the problem persisted. A code reader revealed a P1632 code indicating that the anti-theft system has disabled the fuel system. The owner seeks help to either fix the BCM or bypass the anti-theft system to get the vehicle running.
Professional Technical Analysis
The 1999 Oldsmobile Alero, equipped with a 2.4L I4 engine, has approximately 120,000 miles. The vehicle exhibits symptoms of starting and stalling immediately, with a stored P1632 trouble code indicating that the anti-theft system has disabled the fuel supply. This situation arose after the BCM was disturbed during maintenance, leading to potential issues with the vehicle's security system. The BCM and PCM are interconnected, and any disruption in the BCM can directly affect the PCM, particularly in vehicles with theft deterrent systems like Passlock II. When the BCM was replaced with a used unit, it likely retained the previous vehicle's security settings, which do not match the current vehicle's configuration, leading to the continued P1632 code. The relearning process for the BCM is critical in this case, as it ensures that the vehicle recognizes the new BCM and allows it to communicate correctly with the PCM. If this procedure fails to reset the anti-theft lockout, further programming may be required using a professional scan tool that can interface with the vehicle's security system. The current condition of the vehicle raises safety concerns due to its inability to operate, and the owner should not attempt to bypass the anti-theft system without a thorough understanding of the implications, as this can trigger additional trouble codes like P1631 or P1626.
Possible Causes
Most common causes (ordered by frequency):
- BCM Programming Required: The replacement BCM, being a used part, may not be programmed to the vehicle's security settings. This mismatch can result in the P1632 code, as the vehicle's PCM cannot recognize the BCM. A proper reprogramming procedure must be followed to establish the right security link, which often requires a professional scan tool or dealership service. Typically, BCM programming involves connecting the vehicle to a diagnostic tool that can write the necessary security codes into the BCM. - Persistent P1632 code, security light remains illuminated, BCM replacement did not resolve the issue.
- Improper BCM Installation: If the BCM was not reinstalled correctly after servicing, it could lead to poor contact or intermittent connections that prevent proper communication with the PCM. Wiring harness inspections are essential to ensure all connectors are secure and free of corrosion. Additionally, any loose or damaged wiring can disrupt the signal flow necessary for the anti-theft system to function correctly. - Physical inspection of BCM connectors, signs of corrosion or loose connections, intermittent stalling observed during attempts to start.
- Faulty Wiring or Connector Issues: Wiring related to the BCM may have sustained damage during the initial removal or reinstallation process. This could include issues such as frayed wires, broken connectors, or damaged pins that may compromise the signal integrity. A thorough inspection of the wiring harness and connectors is critical to identify any physical damage that could be causing the P1632 code. - Visual inspection reveals damaged wiring, continuity testing shows open circuits or high resistance in BCM circuits.
- Incompatible Key or Ignition Module: The vehicle's key or ignition module may not be compatible with the new BCM. If the anti-theft system detects a mismatch, it will disable the fuel supply. Verification of the key's coding and the ignition module's functionality is necessary to ensure they are in alignment with the vehicle’s current BCM settings. - Security indicator light behavior inconsistent with key programming, multiple attempts to start without success.
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 Code Retrieval: Use a professional OBD-II scanner or the GeekOBD APP to retrieve the current codes stored in the PCM. Focus on P1632, and verify if any additional codes are present that may provide further insight into the problem. This step is crucial in understanding the vehicle's current state and any related issues.
- STEP 2 - BCM and Wiring Inspection: Conduct a thorough visual and physical inspection of the BCM installation and its wiring harness. Look for signs of corrosion, loose connections, or damaged wires. Any physical damage can affect signal integrity, leading to communication issues between the BCM and PCM that may trigger the P1632 code.
- STEP 3 - BCM Relearning Process: Attempt the BCM relearning process as outlined in the service manual. This usually involves turning the ignition on for approximately 10 minutes after an initial start attempt until the security light goes off. Afterward, turn the ignition off, and then attempt to start the vehicle again. Monitor the security light and check for any changes in the stored codes.
- STEP 4 - Professional Scan Tool Usage: If the BCM relearning process fails, it may be necessary to use a professional scan tool to program the BCM to the vehicle’s specific anti-theft parameters. This step may require taking the vehicle to a dealership or a specialized automotive shop with the necessary equipment to program the BCM correctly.
