2000 Alero - Internal Security
The vehicle theft deterrent system is designed in order to prevent vehicle theft by disabling the fuel injectors unless the lock cylinder is correctly engaged by a mechanical key. The theft deterrent system uses the following 4 components for theft prevention:
• The lock cylinder
• The ignition switch
• The body control module (BCM)
• The powertrain control module (PCM)
When starting the engine, the PCM searches for a password from the BCM through the Class 2 serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. Two modes of tamper detection are provided:
No password received
The engine will start and stall quickly. SECURITY telltale will flash on the instrument panel cluster (IPC) and then stay ON steady.
Incorrect or disable password received (More than 3 invalid passwords are received)
The engine is disabled for at least 10 minutes and the SECURITY telltale will illuminate solid on the IPC during the 10 minutes.
After the vehicle has passed theft detection, the PCM will continue normal operation.
Passlock™ Lock Cylinder
The Passlock™ lock cylinder is a locking cylinder that turns a rotating magnet past a stationary hall effect sensor. This action creates the Passlock™ cylinder data. The Passlock™ cylinder data is sent to the Body Control Module (BCM). The Passlock™ lock cylinder is interfaced with the BCM via a 3-wire connection:
Powertrain Control Module (PCM)
The Powertrain Control Module (PCM) is located on the lower left side of the instrument panel.
The PCM communicates with the Body Control Module (BCM) via serial data over the class 2 serial data bus, CKT 1807. When the BCM determines a passed theft condition, the BCM sends a coded password to the PCM. When the PCM receives the correct password, the PCM enables the fuel injection system, allowing the vehicle to operate correctly. The PCM may allow the car to start and quickly stall during a failed theft condition.
The following conditions may cause the PCM to enter a tamper mode:
• A bad timing cycle
• An incorrect password
If the BCM does not receive a password within a preset time window, the BCM will enter a short tamper mode. During this mode, the PCM will not allow the car to operate for 4 seconds.
If the password is incorrect, the PCM will enter the long tamper mode. In the long tamper mode, the following actions will occur:
• The THEFT SYSTEM indicator will flash.
• The fuel injectors will be shut off for approximately 10 minutes.
Although the vehicle may start, the engine will quickly stall due to a fuel cut-off.
In the event of an open in the serial data communication between the BCM and the PCM, the following actions occur:
• The PCM will become fail-enabled if the car has already passed theft for that ignition cycle (i.e. the engine is running).
• The PCM may set the diagnostic trouble codes (DTC).
• The THEFT SYSTEM indicator will light continuously.
• The PCM will become fail-enabled for future ignition cycles.
If a failure occurs in serial data before the ignition cycle, while the PCM is not fail-enabled, the PCM will never receive a valid password in order to enable the continued use of the fuel injectors.
Your best bet , take to a qualified repair shop .
DTC B2947 Security System Sensor Power CKT Low
DTC B2948 Security System Sensor Power CKT High
DTC B2957 Security System Sensor Data Circuit Low
DTC B2958 Security System Sensor Data Circuit High
DTC B2960 Sec Sys Sensor Data Incorrect but Valid
DTC B3031 Security System Controller in Learn Mode
DTC B3033 Security System Indicates Tamper
on Aug 12, 2017