DESCRIPTION
| WARNING | Deactivate air bag system before performing any service operation. See appropriate AIR BAG RESTRAINT SYSTEMS article. Do not apply electrical power to any component on steering column without first deactivating air bag system. Air bag may deploy. |
Body Control Module (BCM) performs the following functions: A/C compressor request, A/C cooling fan, exterior and interior lighting control, battery rundown protection, chime, gauge control, instrument cluster indicator control and theft deterrent.
BCM communicates with components using class 2 data line and Serial Peripheral Interface (SPI) data line. BCM acts as an interpreter for data communication between class 2 and SPI data systems. Class 2 data line is used by BCM to communicate with the Electronic Brake Control Module (EBCM), Sensing and Diagnostic Module (SDM) and Powertrain Control Module (PCM). Class 2 serial data uses the peer-to-peer method and message arbitration to manage data line traffic.
SPI is a 3-wire synchronous serial data link through which the BCM controls the instrument cluster. BCM interprets driver warnings sent by control module on class 2 data line, then sends a SPI data message to the instrument cluster. SPI data bus essages include fuel gauge position, temperature gauge position, oil pressure, low engine coolant, check oil, volts, ABS, high beam, low fuel, high temperature, washer fluid level low, CRUISE, BRAKE, SERVICE VEHICLE SOON, door ajar, seat belt, theft system, and PRNDL.
Signals that activate the BCM are known as "wake-up" signals. BCM wake-up signals include: door ajar switches, when ignition switch is turned to ON or ACC position, or inadvertent power.
OPERATION
The Powertrain Control Module (PCM) and Body Control Module (BCM) share hardware and software in order to control A/C compressor clutch. The BCM performs the following software functions: limits low speed compressor operation, prevents clutch slippage, monitors for overpressure or high coolant temperature, determines low ambient pressure and controls compressor clutch.
Battery rundown protection (or battery guard) feature provides protection from excessive battery drain caused by high current loads that are accidentally left on. When ignition is turned off, a time-out period is started. If odometer reads less than 15 miles, time-out period will last for 3 minutes. If odometer reads more than 15 miles, time-out period will last for 20 minutes. When time-out expires, inadvertent power output is turned off.
Each time ignition switch is turned from ACC to ON position, BCM controls an instrument cluster bulb check for a calibrated amount of time. During this bulb check, instrument cluster will perform a WOW (gauge needle sweep from low to high to low positions) check.
When BCM activates an indicator in the instrument cluster, it may also produce a chime. The following chimes are provided: key-in-ignition, headlights on, unfastened seat belt, turn signal on, parking brake warning, door ajar warning and check gauges.
Body Control Module (BCM) performs a self-test to detect any internal fault when ignition is turned on. If an internal fault exists, DTC B1000 is set. BCM will refuse all additional inputs if DTC B1000 is set. When DTC B1000 is set, SERVICE VEHICLE SOON indicator will illuminate. Check gauges chime will sound. DTC B1000 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
DTC B1001 will set when radio was not configured properly from factory or when replaced. When DTC B1001 is set, SERVICE VEHICLE SOON indicator will illuminate. Check gauges chime will sound. DTC B1001 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
DTC B1001 will set if Body Control Module (BCM) is not configured properly from factory or when replaced. When DTC B1001 is set, SERVICE VEHICLE SOON indicator will illuminate. Check gauges chime will sound. DTC B1001 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Ignition 0 circuit (Purple wire) provides input from ignition switch to Body Control Module (BCM) and instrument cluster. DTC B1369 will set when Ignition 0 input is not active, and ignition 1 input is active for 20 seconds. See WIRING DIAGRAMS . Vehicle will not start. DTC B1369 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Note. A short to ground will cause fuses to blow. Check for blown BCM BATT (10-amp) and IPC/BCM ACC (10-amp) fuses located in left instrument panel junction block before proceeding with testing.
Ignition 1 circuit (Pink wire) provides input from ignition switch to Body Control Module (BCM). DTC B1374 will set when ignition 1 input is not active with engine running for 20 seconds. See WIRING DIAGRAMS . DTC B1374 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Ignition 3 circuit (Brown wire) provides input from ignition switch to Body Control Module (BCM). DTC B1379 will set when ignition 3 input is not active and ignition 1 input is active for 20 seconds. See WIRING DIAGRAMS . DTC B1379 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Radio receives VIN data over class 2 communication circuit every time ignition switch is cycled between OFF and ON positions. If VIN data in radio memory matches VIN data radio receives over class 2 communication circuit, radio will operate normally. DTC B1780 will set when installing a radio from another vehicle or when installing a new BCM and not entering correct VIN information with scan tool. DTC B1780 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Battery voltage is applied to foglight relay coil when headlights or parking lights are commanded on. Body Control Module (BCM) provides ground to foglight relay. DTC B2532 will set with ignition switch in ON position, headlights or parking lights commanded on and foglight relay control circuit opens or becomes shorted to ground without being commanded by BCM. DTC B2532 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Battery voltage is applied to foglight relay coil when headlights or parking lights are commanded on. Body Control Module (BCM) provides ground to foglight relay. DTC B2533 will set when foglight relay control circuit becomes shorted to voltage. DTC B2533 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Body Control Module (BCM) applies battery voltage to interior lights through inadvertent power control relay. BCM controls interior lights by grounding interior light control circuit. DTC B2558 will set when interior light control circuit becomes shorted to voltage. DTC B2558 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Body Control Module (BCM) turns on Automatic Lighting Control (ALC) headlight relay when ambient light sensor senses a dark condition. BCM grounds ALC headlight relay control circuit. When DTC B2575 is set, SERVICE VEHICLE SOON indicator will illuminate and chime will sound. DTC B2575 can be cleared when BCM reads proper headlight voltage or using scan tool. History DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Body Control Module (BCM) turns on Automatic Lighting Control (ALC) headlight relay when ambient light sensor senses a dark condition. BCM grounds ALC headlight relay control circuit. When DTC B2577 is set, SERVICE VEHICLE SOON indicator will illuminate and chime will sound. DTC B2577 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Body Control Module (BCM) turns on Automatic Lighting Control (ALC) headlight relay when ambient light sensor senses a dark condition. BCM grounds ALC headlight relay control circuit. DTC B2578 will set with ignition switch in ON position, ambient light sensor senses a dark condition, ALC headlights are on and ALC headlight relay control circuit is shorted to voltage for one second or more. When DTC B2578 is set, SERVICE VEHICLE SOON indicator will illuminate and chime will sound. DTC B2578 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Body Control Module (BCM) turns on Automatic Lighting Control (ALC) parking light relay when ambient light sensor senses a dark condition or parking lights are on. BCM grounds ALC parking light relay control circuit.
When DTC B2585 is set, SERVICE VEHICLE SOON indicator will illuminate and chime will sound. DTC B2578 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Body Control Module (BCM) turns on Automatic Lighting Control (ALC) parking light relay when ambient light sensor senses a dark condition. BCM grounds ALC parking light relay control circuit.
When DTC B2587 is set, SERVICE VEHICLE SOON indicator will illuminate and chime will sound. DTC B2587 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
Body Control Module (BCM) turns on Automatic Lighting Control (ALC) parking light relay when ambient light sensor senses a dark condition. BCM grounds ALC parking light relay control circuit.
When DTC B2588 is set, SERVICE VEHICLE SOON indicator will illuminate and chime will sound. DTC B2588 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
BCM grounds Daytime Running Light (DRL) relay control circuit to energize DRL relay coil. DRL relay provides ground to headlights and battery voltage is provided by RT HDLP fuse (15-amp) in underhood junction block. Underhood junction block is located in left side of engine compartment. BCM monitors low and high beam headlight circuits to ensure DRL are operating properly.
When DTC B2600 is set, DRL relay will turn off and SERVICE VEHICLE SOON indicator will illuminate. DTC B2600 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
BCM grounds Daytime Running Light (DRL) relay control circuit to energize DRL relay coil. DRL relay provides ground to headlights and battery voltage is provided by RT HDLP fuse (15-amp) in underhood junction block. Underhood junction block is located in left side of engine compartment.
When DTC B2601 is set, DRL relay will turn off and SERVICE VEHICLE SOON indicator will illuminate. DTC B2601 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
BCM grounds Daytime Running Light (DRL) relay control circuit to energize DRL relay coil. DRL relay provides ground to headlights and battery voltage is provided by RT HDLP fuse (15-amp) in underhood junction block. Underhood junction block is located in left side of engine compartment.
When DTC B2602 is set, DRL relay will turn off and SERVICE VEHICLE SOON indicator will illuminate. DTC B2602 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
DTC B2603 indicates that Daytime Running Lights (DRL) relay output (Light Green/Black wire) is shorted to voltage. When DTC B2603 is set, DRL relay will turn off and SERVICE VEHICLE SOON indicator will illuminate. DTC B2603 can be cleared when fault state is exited when status of DRL returns to off. DTC B2603 can also be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
DTC B2647 indicates that ambient light sensor is shorted to ground or open. BCM supplies 5 volt reference to sensor. Dark conditions are indicated by return voltage of less than 1.5 volts. Light conditions are indicated by return voltage of more than 1.5 volts.
When DTC B2647 is set, headlights will stay on at all times at full intensity, with ignition switch in ON position. DTC B2647 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
DTC B2648 indicates that ambient light sensor is shorted to voltage. When DTC B2648 is set, headlights are disabled, SERVICE VEHICLE SOON indicator will illuminate and chime will sound. DTC B2648 can be cleared using scan tool, or history DTC will disappear after 100 ignition cycles if fault conditions do not reoccur.
DTC U1000 will set when a module does not associate an identification number with at least one critical parameter within about 5 seconds of beginning serial data communication. When more than one critical parameter does not have an identification number associated with it, DTC will only be reported once.
When DTC is set, SERVICE VEHICLE SOON indicator will illuminate and module will use a default value for missing parameter. A current DTC will clear when all critical operating parameters for the module have been associated with an identification number, or at end of current ignition cycle. A history DTC can be cleared using scan tool.
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), the module records the identification number of the module which sent the message for State Of Health (SOH) monitoring. Once an identification 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 identification number for 5 seconds, DTC U1XXX (XXX is equal to the 3-digit identification number) will set. Use DIAGNOSTIC TROUBLE CODE SUFFIX IDENTIFICATION table to determine which system is not communicating. For example, if DTC U1016 is set, 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 that failed module. The modules that can communicate will set a DTC indicating the module that can not communicate.
Current DTC will clear when Node Alive message from the failed identification number is detected on class 2 serial data line or at the end of the current ignition cycle. History DTC can only be cleared using scan tool. If more than one loss of communication DTC is set in either one or multiple modules, perform diagnosis in the following order
- Current DTCs before history DTCs, unless otherwise indicated in testing procedure.
- DTC which is reported the most times.
- From lowest number DTC to highest number DTC.
| Module Not Communicating | DTC Suffix |
|---|---|
| Body Control Module | 064 |
| Electronic Brake Control Module | 040 |
| Integrated Radio Chassis | 128 |
| Powertrain Control Module | 016 |
| Sensing And Diagnostic Module | 088 |
DIAGNOSTIC TROUBLE CODE SUFFIX IDENTIFICATION
Modules connected to class 2 serial data circuit monitor for serial data communications during vehicle operation. A State Of Health (SOH) message is communicated from each module to all other modules every 2 seconds. If a module detects low voltage and no SOH messages along class 2 serial data line for approximately 3 seconds, DTC U1300 will set. When DTC U1300 is set, no additional communication DTCs (communication DTCs begin with "U") can set.
Current DTC will clear when valid class 2 message is detected on class 2 serial data line or at end of current ignition cycle (key off). History DTC will clear only with scan tool.
Modules connected to class 2 serial data circuit monitor for serial data communications during vehicle operation. A State Of Health (SOH) message is communicated from each module to all other modules every 2 seconds. If a module detects high voltage and no SOH messages along class 2 serial data line for approximately 3 seconds, DTC U1301 will set. When DTC U1301 is set, no additional communication DTCs (communication DTCs begin with "U") can set.
Current DTC will clear when valid class 2 message is detected on class 2 serial data line or at end of current ignition cycle (key off). History DTC will clear only with scan tool.
Instrument Panel Cluster (IPC) and Body Control Module (BCM) communicate over Serial Peripheral Interface (SPI). IPC receives information from BCM over SPI serial data out circuit. BCM transmits information to IPC in order to control various indicators. BCM receives data from IPC over SPI serial data in circuit. IPC transmits information such as tachometer active status, speedometer active status and invalid data received messages. BCM synchronizes data signals by toggling SPI serial data clock circuit to ground.
When DTCs U2000, U2004, U2005, U2006 or U2007 are set, fuel gauge will display empty and temperature gauge will display 100° F. THEFT SYSTEM, ABS and SERVICE VEHICLE SOON indicators will illuminate. A current DTC U2000-U2007 will clear on next malfunction free ignition cycle. A history DTC U2000-U2007 will clear after 100 ignition cycles if fault conditions do not reoccur. Scan tool can be used to clear current or history DTC U2000-U2007.