Body Control Modules: Overview Oldsmobile Alero I

DESCRIPTION

The Body Control Module (BCM) controls many vehicle functions. These functions include A/C compressor, audible warnings (chime), battery rundown protection, instrument panel cluster indicators and gauges, interior and exterior lighting, theft deterrent, keyless entry and panic horn. Battery voltage is provided to BCM from left instrument panel junction block fuse BFC/BATT (10-amp).

BCM communicates with other systems over class 2 serial data line to execute various vehicle functions. Communication between each system is accomplished by sending digitally coded messages, which consist of specific information the system module must follow. Each system module is assigned its own recognition code, so that it can respond to appropriate messages.

Other modules that communicate with the BCM over class 2 serial line are the Electronic Brake Control Module (EBCM), Instrument Panel Cluster (IPC), Powertrain Control Module (PCM) and the inflatable restraint Sensing and Diagnostic Module (SDM).

Test Description

These diagnostic procedures will help find and repair air bag system malfunctions. For best results, use the diagnostic tables, and follow the sequence listed below.

1. Refer to the diagnostic table as directed by the air bag diagnostic system check. The diagnostic tables will help you to diagnose any SIR system malfunction. Bypassing these procedures may result in extended diagnostic time, incorrect diagnosis, or possible incorrect parts replacement.
2. Repeat the air bag diagnostic system check after you perform any repair or diagnostic procedures. This will verify that you correctly performed the repair. This will also ensure that no other malfunctions exist.

The Anti-Lock Brake System (ABS) diagnostic system check is an organized approach to identify problems associated with the Electronic Brake Control Module (EBCM). This check must be the starting point for any EBCM complaint, and will direct you to the next logical step in diagnosing the complaint. The EBCM is a very reliable component and is not likely the cause of the malfunction. Most system complaints are linked to faulty wiring, connectors, and occasionally to components. Understanding the ABS and using the tables correctly will reduce diagnostic time and prevent unnecessary parts replacement.

Powertrain Control Module (PCM) diagnostic system check is an organized approach to identifying a condition that is created by a malfunction in powertrain control system. Diagnostic system check must be the starting point for any driveability concern. Diagnostic system check directs the service technician to the next logical step in order to diagnose the concern. Understanding and correctly using the diagnostic table reduces diagnostic time, and prevents replacement of good parts.

If PCM stores multiple powertrain DTCs, diagnose the DTCs in the following order

1. Component level DTCs, such as sensor DTCs, solenoid DTCs, and relay DTCs. Diagnose the multiple DTCs within this category in numerical order. Begin with the lowest numbered DTC, unless the diagnostic table directs you otherwise.
2. System level DTCs, for example, misfire DTCs, fuel trim DTCs, and catalyst DTCs.

Powertrain Control Module (PCM) diagnostic system check is an organized approach to identifying a condition that is created by a malfunction in powertrain control system. Diagnostic system check must be the starting point for any driveability concern. Diagnostic system check directs the service technician to the next logical step in order to diagnose the concern. Understanding and correctly using the diagnostic table reduces diagnostic time, and prevents replacement of good parts.

If Powertrain Control Module (PCM) stores multiple powertrain DTCs, diagnose the DTCs in the following order

1. Component level DTCs, such as sensor DTCs, solenoid DTCs, and relay DTCs. Diagnose the multiple DTCs within this category in numerical order. Begin with the lowest numbered DTC, unless the diagnostic table directs you otherwise.
2. System level DTCs, for example, misfire DTCs, fuel trim DTCs, and catalyst DTCs.

Body Control Module (BCM) performs a self-test when ignition switch is turned to RUN position. If BCM detects an internal error, DTC B1000 sets, SERVICE VEHICLE SOON light illuminates and the check gauges chime sounds.

DTC B1369 will set if IGNITION 0 input is not active after IGNITION 1 input has been active for 20 seconds. When DTC is present, multiple indicators on the instrument panel will illuminate and vehicle will not start. A current DTC B1369 will clear when fault is no longer present and ignition switch is cycled. A history DTC B1369 clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DTC B1374 will set if IGNITION 1 input is not active after engine has been running for 20 seconds. When DTC is present, SERVICE VEHICLE SOON indicator illuminates and check gauges chime will sound. A current DTC B1374 will clear when fault is no longer present and ignition switch is cycled. A history DTC B1374 clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DTC B1379 will set if IGNITION 3 is not active after IGNITION 1 has been active for 20 seconds. When DTC is present, SERVICE VEHICLE SOON indicator illuminates and check gauges chime will sound. A current DTC B1379 will clear when fault is no longer present and ignition switch is cycled. A history DTC B1379 clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

The Body Control Module (BCM) monitors ignition key alarm switch. When DTC is present, BCM assumes key-in-ignition input is active and interior lights will not illuminate after key is removed from ignition switch. DTC B2965 becomes a history DTC when fault is no longer present. History DTC B2965 is cleared after 100 consecutive ignition cycles if condition for malfunction is no longer present, or BCM receives clear code command from scan tool.

Class 2 serial data line is used to communicate information and commands between modules. When a module receives a message for a critical operating parameter, module records ID number of module which sent message for State Of Health (SOH) monitoring. A critical operating parameter is one which, when not received requires receiving module use a default value for that parameter.

DTC will set when a module does not associate an ID number with at least one critical parameter within about 5 seconds after beginning communication. When more than one critical parameter does not have an ID number associated with it, DTC will be reported once. When DTC is present, SERVICE VEHICLE SOON indicator illuminates and module will use a default value for missing critical parameter.

A current DTC U1000 will clear when all critical operating parameters have been associated with an ID number, or at the end of current ignition cycle. A history DTC can only be cleared with a scan tool command.

Class 2 serial data line is used to communicate information and commands between modules. When a module receives a message for a critical operating parameter, (Node Alive message) module records ID number of module which sent message for State Of Health (SOH) monitoring. A critical operating parameter is one which, when not received requires receiving module to use a default value for that parameter. Once an ID number is learned by a module, it will monitor for that module's Node Alive message. Each module on serial data line is required to send a Node Alive message every 2 seconds. When no message is detected from a learned ID number for 10 seconds, DTC U1XXX (XXX is equal to the 3-digit identification number) will set. Use DIAGNOSTIC TROUBLE CODE ID NUMBER table to determine which system is not communicating. For example, if DTC U1016 is stored, Powertrain Control Module (PCM) is not communicating. A module with a class 2 serial data line malfunction or which loses power during a current ignition cycle will have a loss of communication DTC set by other modules that depend on information from faulty module. Modules that can communicate will store a DTC indicating which module can not communicate.

Current DTC will clear when Node Alive message from failed identification number is detected on class 2 serial data line or at end of the current ignition cycle. History DTC will be cleared after 50 ignition cycles as long as there are no other failures.

If more than one loss of communication DTC is stored in either one or multiple modules, perform diagnosis in the following order

1. Current DTCs before history DTCs, unless otherwise indicated in testing procedure.
2. DTC which is reported the most times.
3. From lowest number DTC to highest number DTC.

DIAGNOSTIC TROUBLE CODE ID NUMBER

Serial data line is used to communicate information and commands between modules. In addition, Node Alive (State Of Health) messages are transmitted by each module on serial data line about once every 2 seconds. When a module detects no messages and a low voltage on serial data line for about 10 seconds, DTC U1300 is stored. Setting of all other class 2 serial communication DTCs is inhibited and module uses default values for all parameters received on class 2 serial data line. DTC U1300 will set when: No valid messages are detected on class 2 serial data circuit. Voltage level detected on class 2 serial data circuit is low. Above conditions are met for approximately 3 seconds.

A current DTC U1300 will clear when a valid class 2 message is detected on serial data line or at end of current ignition cycle. History DTC will be cleared after 50 ignition cycles as long as there are no other failures.

Serial data line is used to communicate information and commands between modules. In addition, Node Alive (State Of Health) messages are transmitted by each module on serial data line about once every 2 seconds. When a module detects no messages and a high voltage on serial data line for about 10 seconds, DTC U1301 is stored. Setting of all other class 2 serial communication DTCs is inhibited and module uses default values for all parameters received on class 2 serial data line. DTC U1301 is set when: No valid messages are detected on class 2 serial data circuit. No valid messages are detected on the class 2 serial data circuit. The voltage level detected on the class 2 serial data circuit is high. The above conditions are met for approximately 3 seconds. Voltage level detected on class 2 serial data circuit is high. Above conditions are met for approximately 3 seconds.

A current DTC U1301 will clear when a valid class 2 message is detected on serial data line or at end of current ignition cycle. History DTC will be cleared after 50 ignition cycles as long as there are no other failures.

The Data Link Connector (DLC) provides operating power for the scan tool at terminal No. 16 (battery positive voltage) and at terminal No. 4 (battery ground). The DLC provides the class 2 serial data signal at terminal No. 2 and signal ground at terminal No. 5. The scan tool will power up with the ignition switch is in OFF position. Many modules, however, may not communicate unless the ignition switch is in RUN position.

Modules connected to class 2 serial data line monitor serial data communications during normal vehicle operation. Operating information and commands are exchanged between modules. Connecting scan tool to Data Link Connector (DLC) allows communication with modules for diagnostics. The engine will not start when there is a complete malfunction of class 2 serial data line while engine is off.