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BCM Basics 101 (07-13)

itsstopher

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Body Control System Description and Operation

The body control system consists of the body control module (BCM), communications, and various input and outputs. Some inputs, outputs and messages require other modules to interact with the BCM. The BCM also has discrete input and output terminals to control the vehicle's body functions. The BCM is wired to the GMLAN high speed serial data buss and the GMLAN low speed serial data buss and acts as a gateway between them. If the BCM does not communicate the vehicle will not start due to the inability of the engine control module (ECM)/powertrain control module (PCM) and theft deterrent module (TDM) to communicate without the BCM providing the gateway function.

Power Mode Master

This vehicles body control module (BCM) functions as the power mode master (PMM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination the power mode that will be sent over the serial data circuits to the other modules that need this information, and so the PMM will activate relays and other direct outputs of the PMM as needed.

Serial Data Gateway

The body control module (BCM) in this vehicle functions as a gateway or translator. The purpose of the gateway is to translate serial data messages between the GMLAN high speed buss and the GMLAN low speed buss for communication between the various modules. The gateway will interact with each network according to that network's transmission protocol.

One example of this necessary communication is the communication between the engine control module (ECM)/powertrain control module (PCM) which is high speed serial data and Theft Deterrent Module which is low speed serial data. If these modules can not exchange information, the vehicle will not start.

Communication between the BCM and a scan tool can be on the high speed GMLAN network or low speed GMLAN network. If one network is lost, the BCM can still communicate with the scan tool. A lost communication DTC typically is set in modules other than the module with a communication failure.

Body Control Module

The various body control module (BCM) input and output circuits are described in the corresponding functional areas indicated on the BCM electrical schematics. Some BCM functions with the subsystems may be as a gateway only or as an enable for the system. The BCM related systems/subsystems include, but are not limited to the following:

   ?  Antilock Brake System (ABS)
   ?  Automatic Day-Night Mirror
   ?  Cruise Control System
   ?  Electrical Power Management (EPM)
   ?  Exterior Lighting
   ?  Horn System
   ?  HVAC
   ?  Instrument Cluster Indicator Control
   ?  Interior Lighting
   ?  Power Door Lock System
   ?  Rear Window Defogger System
   ?  Redundant Steering Wheel Controls
   ?  Remote Function Actuation (RFA) Control
   ?  Retained Accessory Power (RAP)
   ?  Shift Lock Control System
   ?  Starting System
   ?  Supplemental Inflatable Restraint (SIR) System
   ?  Suspension System
   ?  Theft Deterrent
   ?  Tire Pressure Monitor (TPM) System
   ?  Wiper/Washer System Functions


(1) I/P Trim
(2) I/P Cluster Trim
(3) Floor Panel
(4) Junction Block - Left I/P
(5) Body Control Module (BCM)
(6) Transfer Case Shift Control Module (NP:cool:
(7) Fuse Block - I/P
 

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itsstopher

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Body Control Module (BCM) C1 (light green)

Pin        Wire Color        Function
1                --                 Not Used
2             PK/BK             Ignition 0 Voltage
3               GY                Cruise Control Switch Signal
4               WH               5-Volt Reference
5             L-GN               Windshield Wiper Switch High Signal
6             L-GN               Steering Wheel Control Switch Signal
7                --                 Not Used
8             TN/BK             Low Reference
9              L-BU              Windshield Wiper Switch Low Signal
10-13        --                  Not Used
14             PK                 Ignition 1 Voltage
15            D-GN              Hazard Switch Left Turn Signal
16             TN                 Hazard Switch Right Turn Signal
17             PK                 12-Volt Reference
18             YE                  Headlamp Dimmer Switch Signal
19            WH                 Hazard Switch Signal
20            PU                   Tap Up/Tap Down Switch Signal (MYC)
21            BN                  Ignition 1 Voltage
22             --                   Not Used
23           L-BU                 Tow/Haul Switch Signal
24             PK                  Windshield Washer Switch Signal
25             YE                   Headlamp Flash to Pass Signal
26          TN/WH               A/T Shift Lock Solenoid Supply Voltage
27             --                    Not Used
 

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itsstopher

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Body Control Module (BCM) C2 (natural)

Pin        Wire Color     Function
1                OG           Inadvertent Power Control
2             RD/WH        Battery Positive Voltage
3             BN/WH        Instrument Panel Lamp Dimming Control
4                --             Not Used
5               GY             Interior Lamp Control
6-7            --              Not Used
8              L-BU           Headlamp Switch Park Lamp Signal
9-10          --              Not Used
11            WH            Ambient Light Sensor Signal
12            WH            Headlamp Switch On Signal
13-16        --              Not Used
17           D-GN           Headlamp Switch Headlamps Off Signal
18        D-BU/WH       Courtesy Lamp Supply Voltage
19             --              Not Used
20            PU             Right Tail Lamp Outage Detection Signal (Z75)
21           L-BU           Traction Control Switch Signal
22           D-BU           Backup Lamp Relay Control
23-24        --              Not Used
25            PU              Interior Lamp Switch Voltage Supply Voltage
 

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itsstopher

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Body Control Module (BCM) C3 Pin (light blue)

Pin        Wire Color     Function
1             BK/WH         Ground
2             RD/WH         Battery Positive Voltage
3             RD/WH         Battery Positive Voltage
4                 --              Not Used
5             BK/WH          Ground
6-7              --              Not Used
8              TN/BK          High Speed GMLAN Serial Data Bus +
9                TN             High Speed GMLAN Serial Data Bus -
10            D-GN           Low Speed GMLAN Serial Data
11            D-GN           Instrument Panel Lamps Dimmer Switch Signal
12           OG/WH         12-Volt Reference or I/P Dimming Voltage Reference
13              PU             Brake Pedal Switch Normally Closed Contact Signal
14-15          --              Not Used
16            TN/BK          High Speed GMLAN Serial Data Bus +
17              TN             High Speed GMLAN Serial Data Bus -
18              YE             LED Backlight Dimming Control
19            L-BU           Serial Data Communication Enable
20              --               Not Used
21             OG              Front Fog Lamp Switch Signal (T96)
22        L-GN/WH          Cruise Control Indicator Dimming Signal
23-24         --               Not Used
25           PU/WH          Indicator Dimming Control
 

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itsstopher

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Body Control Module (BCM) C4 (light blue)

Pin        Wire Color     Function
1              RD/WH       Battery Positive Voltage
2              RD/WH       Battery Positive Voltage
3              RD/WH       Battery Positive Voltage
4              RD/WH       Battery Positive Voltage
5             D-BU/WH     Right Front Turn Signal Lamp Supply Voltage
6                  --            Not Used
7                 YE            Windshield Wiper Motor Park Switch Signal
8                  --             Not Used
9              BK/WH         Ground
10            RD/WH        Battery Positive Voltage
11          D-GN/WH      Fog Lamp Relay Control (T96)
12                YE           Right Trailer Turn Signal Lamp
13               OG           Left Trailer Turn Signal Lamp
14              L-GN         Outside Moisture Sensor Signal 2 (CE1)
15               OG           Windshield Washer Relay Control
16             TN/WH       Headlamp High Beam Relay Control
17             PK/BK        Hood Ajar Switch Signal
18               TN            Outside Moisture Sensor Signal 1 (CE1)
19              D-BU         Accessory Wakeup Serial Data
20                --            Not Used
21               YE            Run/Crank Relay Coil Control
22                --            Not Used
23            L-GN/BK      DRL Relay Control
24-25           --            Not Used
 

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itsstopher

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Body Control Module (BCM) C5 (light blue)

Pin        Wire Color     Function
1               YE/BK        Left Rear Turn Signal Lamp Supply Voltage (X88/Z88/Z75 Export w/E52)
                  YE           Left Rear Stop/Turn Lamp Supply Voltage (X88 Except E52/Domestic Z75)
2            D-GN/WH     Right Rear Turn Signal Lamp Supply Voltage (X88/Z88/Z75 Export w/E52)
                D-GN         Right Rear Stop/Turn Lamp Supply Voltage (X88 Except E52/Domestic Z75)
3                 --            Not Used
4           L-BU/WH       Left Front Turn Signal Lamp Supply Voltage
5               L-BU          CHMSL Supply Voltage
6           L-BU/WH       Cruise/ETC/TCC Brake Signal
7               WH            Headlamp Washer Relay Control (CE4)
8                PK            Current Sensor Supply Voltage
9               WH            Current Sensor Signal
10             BN             Current Sensor Low Reference
11             YE              Accessory Voltage
12              --              Not Used
13             OG             Ignition 3 Voltage
14            WH             Rear Wiper/Washer Switch Supply Voltage
15             PU              Hood Closed Switch Signal
16            L-BU            Park Brake Switch Signal
17              YE              Left Tail Lamp Outage Detection Signal (Z75)
18             TN               Horn Relay Control
19             YE               Out of Park Signal
20             GY               Windshield Wiper Switch Signal 2
21              TN              Front Windshield Wiper Switch High Signal
22              --                Not Used
23          PK/WH           Headlamp Low Beam Relay Control
24           D-BU             Park Lamp Relay Control
25              --               Not Used
 

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itsstopher

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Body Control Module (BCM) C6 (light blue)

Pin        Wire Color     Function
1                 --             Not Used
2               L-BU          Stop Lamp Supply Voltage
3-11            --             Not Used
12            PK/BK         Liftgate Ajar Switch Signal (E52 Except E61)
13              GY            Rear Closure Handle Switch Open Signal (E52 Except E61)
14          L-GN/BK       Right Rear Door Ajar Switch Signal
15          L-BU/BK       Left Rear Door Ajar Switch Signal
16              OG           Non-Driver Door Open Switch Signal
17-21         --             Not Used
22            L-GN          Rear Access Open Switch Signal (E52 Except E61)
23              --             Not Used
24              PK            Lift Glass/Trunk Exterior Release Signal (E52 Except E61)
25              --              Not Used
 

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itsstopher

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Body Control Module (BCM) C7 (light blue)

Pin        Wire Color      Function
1                YE             Endgate Latch Relay Coil Control (E52 Except E61)
2                TN             Lift Glass/Trunk Motor Release Control (E52 Except E61)
3              D-GN           Endgate Latch Relay Supply Voltage (E52 Except E61)
4-6             --              Not Used
7              L-BU            Door Lock Control
8                 --              Not Used
9               WH            Door Unlock Control
10-17          --             Not Used
18             L-GN          Power Window Master Switch Right Rear Up Signal
19              PU            Power Window Master Switch Left Rear Down Signal
20               --             Not Used
21             D-BU          Power Window Master Switch Lockout Signal
22-25          --             Not Used
26               PU           Power Window Master Switch Right Rear Down Signal
27          L-BU/WH      Power Window Master Switch Lockout Right Rear Signal
28             D-GN         Power Window Master Switch Left Rear Up Signal
 

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