data line_bcm control schematics

Data Link Communications Description

and Operation

Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the class 2

serial data line. The serial data line is the means by which the microprocessor-

controlled modules in the vehicle communicate with each other. Once the scan

tool is connected to the class 2 serial data line through the DLC, the scan tool

can be used to monitor each module for diagnostic purposes and to check for

diagnostic trouble codes (DTCs). Class 2 serial data is transmitted on a single

wire at an average of 10.4 kbps. This value is an average, class 2 uses a

variable pulse width modulation to carry data and depending on the message it

may operate faster or slower. The bus will float at a nominal 7 volts during normal

operation. Each module can pull this lower during the transmission. The bus is

not at battery positive voltage or ground potential during normal operation. When

the ignition switch is in RUN, each module communicating on the class 2 serial

data line sends a state of health (SOH) message every 2 seconds to ensure that

the module is operating properly. When a module stops communicating on the

class 2 serial data line, for example if the module loses power or ground, the

SOH message it normally sends on the data line every 2 seconds disappears.

Other modules on the class 2 serial data line, which expect to receive that SOH

message, detect its absence; those modules in turn set an internal DTC

associated with the loss of SOH of the non-communicating module. The DTC is

unique to the module which is not communicating, for example, when the

inflatable restraint sensing and diagnostic module (SDM) SOH message

http://service.gm.com/servlets/#oth1-1573277


























disappears, several modules set DTC U1088. Note that a loss of serial data DTC

does not normally represent a failure of the module that set it.

Data Link Connector (DLC)

The data link connector (DLC) is a standardized 16-cavity connector. Connector

design and location is dictated by an industry wide standard, and is required to

provide the following:

• Scan tool power battery positive voltage at terminal 16

• Scan tool power ground at terminal 4

• Class 2 serial data at terminal 2

• Common signal ground at terminal 5

Class 2 Serial Data Line

The class 2 serial data line on this vehicle is a combination star-linear

configuration, where the body control module (BCM) is connected to multiple

modules. Refer to Data Link Connector (DLC) Schematics for schematics. The

following modules communicate on class 2 bus:

• The BCM

• The electronic brake control module (EBCM)

• The inflatable restraint sensing and diagnostic module (SDM)

• The instrument panel cluster (IPC)

• The powertrain control module (PCM)

• The radio

• The rear seat entertainment (RSE) assembly

• The transfer case shift control module (TCSCM)

• The vehicle communication interface module (VCIM) (OnStar®)

http://service.gm.com/servlets/#ss2-1552135




http://service.gm.com/servlets/CellHandler?CellId=72801&RefDoc=1552135&evc=sm

Body Control System Description and

Operation

BCM Functions

The body control module (BCM) performs multiple body control functions. The

BCM can control devices directly connected to its outputs based on input

information. The BCM evaluates this information and controls certain body

control systems by commanding outputs on or off. The BCM control inputs can

be:

• Sensors and switches that are directly connected to the BCM

• Class 2 serial data received from other control modules connected to the class 2

serial data link.

The BCM is also capable of controlling other vehicle systems that are not directly

wired to the BCM. The BCM does this by sending specific messages on the class

2 serial data link. The control module capable of performing the required function

will respond to the BCM message.

The BCM controls these functions:

• Audible warnings--Refer to Audible Warnings Description and Operation in

Instrument Panel, Gages and Console.

• Automatic door locks--Refer to Power Door Locks Description and Operation in

Doors.

• Automatic headlamp control--Refer to Exterior Lighting Systems Description and

Operation in Lighting Systems.

• Horns--Refer to Horns System Description and Operation in Horns.

• Interior lighting--Refer to Interior Lighting Systems Description and Operation in

Lighting Systems.

• Keyless entry--Refer to Keyless Entry System Description and Operation in Keyless

Entry.

• Passlock theft deterrent--Refer to Vehicle Theft Deterrent (VTD) Description and

Operation in Theft Deterrent.














• Retained Accessory Power (RAP)--Refer to Retained Accessory Power (RAP)

Description and Operation .

• Front Wipers/Washer--Refer to Wiper/Washer System Description and Operation in

Wipers/Washer.

• Rear Wipers/Washer--Refer to Rear Wiper/Washer System Description and

Operation in Wipers/Washer.

• Sunroof--Refer to Sunroof Description and Operation in Roof

Power Mode

The BCM is the power mode master (PMM). Refer to Power Mode Description

and Operation for more information.














Power Mode Description and Operation

Serial Data Power Mode

On vehicles that have several control modules connected by serial data circuits,

one module is the power mode master (PMM). On this vehicle the PMM is the

body control module (BCM). The BCM uses 3 signals from the ignition switch:

• Ignition Off/Run/Crank

• Ignition 1 Run/Crank

• Ignition Accessory

To determine the correct power mode the BCM uses:

• The state of these signals

• The sequence of switch closures received by the BCM

• The status of the engine run flag (ERF)

The chart indicates the power modes detected and transmitted by the BCM:

Correct Ignition

Switch Inputs and

Power Modes

Ignition Switch

Position

ERF

BCM Input and Scan Tool Display

Ignition

Accessory

Ignition 1

Run/Crank

Ignition

Off/Run/Crank

Power

Mode

OFF 0 Inactive Inactive Active Off-Awake

or RAP

ACC 0 Active Inactive Inactive Accessory

ON 0 Active Active Active Run

START 0 Inactive Active Active Crank



http://service.gm.com/servlets/#tab2-1552140





ON 1 Active Active Active Run

Fail-safe Operation

Since the operation of the vehicle systems depends on the power mode, there is

a fail-safe plan in place should the body control module (BCM) fail to send a

power mode message. The fail-safe plan covers modules with discrete ignition

signal inputs as well as those modules using exclusively serial data control of

power mode.

Serial Data Messages

The modules that depend exclusively on serial data messages for power modes

stay in the state dictated by the last valid BCM message until they receive the

engine status from the powertrain control module (PCM). If the BCM fails, the

modules monitor the serial data circuit for the engine run flag serial data. If the

engine run flag serial data is true, indicating that the engine is running, the

modules fail-safe to Run. In this state the modules and their subsystems can

support all operator requirements. If the engine run flag serial data is false,

indicating that the engine is not running, the modules fail-safe to OFF-AWAKE. In

this state the modules are constantly checking for a change status message on

the serial data circuits and can respond to both local inputs and serial data inputs

from other modules on the vehicle.

Discrete Ignition Signals

Those modules that have discrete ignition signal inputs also remain in the state

dictated by the last valid BCM message received on the serial data circuits. They

then check the state of their discrete ignition input to determine the current valid

state. If the discrete ignition input is active, B+, the modules will fail-safe to the

RUN power mode. If the discrete ignition input is not active, open or 0 voltage,

the modules will fail-safe to OFF-AWAKE. In this state the modules are

constantly checking for a change status message on the serial data circuits and



can respond to both local inputs and serial data inputs from other modules on the

vehicle.

Retained Accessory Power (RAP)

Description and Operation

Serial Data Control of Retained Accessory Power (RAP)

The class 2 modules receive the power mode message from the body control

module (BCM) over the serial data circuits, indicating when the retained

accessory power (RAP) power mode is current. The BCM monitors the ignition

switch position, battery condition and passenger compartment doors status to

determine whether RAP should be initiated. The modules then support the

operation of the systems under their control as required by their RAP power

mode operation.

RAP will end when one of the following conditions is met:

• The BCM receives an input indicating the opening of any compartment door.

• The BCM internal timer for the RAP expires after approximately 10 minutes.

• The BCM detects a decrease in battery capacity below a prescribed limit.

The BCM then sends a serial data power mode message Off-Awake ending the

RAP function.

The modules that perform normally during RAP are:

• The radio

• The rear seat entertainment (RSE) assembly

• The vehicle communication interface module (VCIM) (OnStar®)

Relay Control of Retained Accessory Power (RAP)

The BCM keeps the RAP/ACC relay energized during all power modes, except

Off-Awake. The RAP/ACC relay provides power to the following systems:

• Power windows





• Sunroof

• Front wiper/washer

• Rear wiper/washer

FIGURE Power, Ground, and Subsystem References to DLC, A/T Shift Lock

Control, HVAC, Starting and Charging, Engine Controls, and Door Lock/Indicator

Systems(c)

FIGURE Subsystem References to ABS, Horn, Theft, and Wiper/Washer

Systems(c)





FIGURE Subsystem References to Doors, Interior Lights and Interior Lights

Dimming Systems(c)





FIGURE Subsystem References to Exterior Lighting and Fog Lights(c)




Data Link Connector (DLC) Schematics

Retained Accessory Power (RAP)

Schematics

Computer/Integrating Systems

Connector End Views

Connector 1: Body Control Module (BCM) C1

Connector 2: Body Control Module (BCM) C2

Connector 3: Data Link Connector (DLC)

Body Control Module (BCM) C1

Connector Part Information

OEM: 15480437

Service: 88988604

Description: 56-Way F GT 280/Micro 64 Series (BK)

Terminal Part Information

Pins: A2-A6, A8-A48

Terminal/Tray: 15359541/4

Core/Insulation Crimp: M/M

Release Tool/Test Probe: 15381651-2/J-35616-64A (L-BU)

Pins: A7, B1-B8








Core/Insulation Crimp: Pins B3-B4, B6-B8: E/A, Pins A7, B1-B2, B5: 2/A

Release Tool/Test Probe: 15315247/J-35616-4A (PU)

Body Control Module

(BCM) C1

Pin

Wire

Color

Circuit

No. Function

A1 -- -- Not Used

A2 YE 317 Fog Lamp Relay Control

A3 L-BU 14 Left Turn Signal Lamp Supply

Voltage

A4 -- -- Not Used

A5 PK/WH 1970 Headlamp Relay Control

A6 BK 755 RAP Relay Coil Control

A7 OG 2040 Battery Positive Voltage

A8 D-GN 113 Windshield Wiper Switch Signal 2

A9 -- -- Not Used

A10 WH 193 Rear Defog Relay Control

A11 L-BU 244 Passenger Door Lock Switch Lock

Control

A12 WH 194 Door Unlock Control

A13-A17 -- -- Not Used

A18 BK/WH 1969 Headlamp High Beam Relay

Control

A19 D-BU 15 Right Turn Signal Lamps Supply

Voltage

A20 YE 196 Windshield Wiper Motor Park





Switch Signal


A24 BN/WH 301 Park Lamp Relay Control

A25 -- -- Not Used

A26 RD/BK 1594 Ignition 3 Relay Control


A29 OG 1732 Inadvertant Power Supply Voltage


A31 L-BU 1134 Park Brake Switch Signal

A32 GY/BK 745 Left Front Door Ajar Switch Signal


A37 L-BU 20 Stop Lamp Supply Voltage

A38 L-GN/BK 748 Right Front Door Ajar Switch

Signal

A39 BK/WH 746 Left Rear Door Ajar Switch Signal

A40 BK 28 Horn Relay Control

A41 PU 1807 Class 2 Serial Data


A43 D-

GN/WH 762 A/C Request Signal

A44 L-BU/BK 747 Right Rear Door Ajar Switch

Signal

A45 -- -- Not Used

A46 WH 156 Courtesy Lamp Low Control


A48 BN 2509 Left Rear Park Lamps Supply

Voltage

B1 YE 18 Left Rear Stop/Turn Lamp Supply

Voltage

B2 D-GN 19 Right Rear Stop/Turn Lamp

Supply Voltage

B3 BK/WH 1251 Ground

B4 RD 228 Windshield Washer Pump Control

B5 OG 840 Battery Positive Voltage

B6 D-BU 338 Run/Crank Voltage

B7 BN 4 Accessory Voltage

B8 OG 1340 Battery Positive Voltage

Body Control Module (BCM) C2


OEM: 15480439

Service: 88988604

Description: 56-Way F GT 280/Micro 64 Series (GY)





Pins: A1-A48


Core/Insulation Crimp: M/M

Release Tool/Test Probe: 15381651-2/J-35616-64A (L-BU)

Pins: B5-B8


Core/Insulation Crimp: E/A

Release Tool/Test Probe: 15315247/J-35616-4A (PU)

Body Control Module

(BCM) C2

Pin

Wire

Color

Circuit

No. Function

A1 PU 524 Headlamp Dimmer Switch High

Beam Signal

A2 WH 103 Headlamp Switch Headlamps On

Signal

A3 GY 112 Windshield Wiper Switch Signal 1

A4 BN/WH 230 Instrument Panel Lamps Dimming

Control

A5 YE 183 Front Fog Lamp Indicator Control

A6 L-BU 2114 Left Rear Turn Signal Lamp Supply

Voltage

A7 BN/WH 301 Park Lamp Switch Signal

A8 BN 1356 Flash To Pass Switch Signal

A9 PU/WH 549 Headlamp Switch Headlamps Off

Signal

A10 PU 719 Low Reference





A11 D-

BU/WH 1495 Dome Override Switch Signal

A12 PU 328 Interior Lamp Switch Signal

A13 D-

BU/WH 6796

ONSTAR Voice Recognition Switch

Signal

A14 WH 1390 Off/Run/Crank Voltage


A17 BN/WH 1571 Traction Control Switch Signal

A18 OG 192 Front Fog Lamp Switch Signal

A19 GY 728 Security Indicator Control


A24 L-BU 292 Rear Defog Switch Signal

A25 BK 28 Horn Relay Control

A26 D-BU 2115 TCS Requested Indicator Control

A27 GY 8 Instrument Panel Lamps Dimmer

Switch Signal


Switch Signal


Switch Signal


Switch Signal

A31 BN 323 Shift Solenoid Supply Voltage

A32 TN 683 Rear Defog Indicator Supply

Voltage


Switch Signal


Switch Signal

A35 -- -- Not Used


Switch Signal

A37 WH 278 Ambient Light Sensor Signal





A42 WH/BK 1073 Ignition Key Resistor Signal

A43 BK 279 Ambient Light Sensor Low

Reference


A45 L-BU 1508 Turn Signal Switch Signal

A46 OG 1732 Courtesy Lamp Supply Voltage


A48 WH 111 Hazard Switch Signal

B1-B4 -- -- Not Used

B5 RD 228 Windshield Washer Pump Control

B6 -- -- Not Used

B7 BN 4 Accessory Voltage

B8 D-BU 338 Run/Crank Voltage




OEM: 15317575

Service: See Catalog

Description: 16-Way F Metri-Pack 150 Series (BK)


Pins: 2, 4


Core/Insulation Crimp: See Terminal Kit

Release Tool/Test Probe: See Terminal Kit

Pins: 5, 16


Core/Insulation Crimp: E/A

Release Tool/Test Probe: 12094429/J-35616-2A (GY)


Pin

Wire Color Circuit No. Function

1 -- -- Not Used

2 PU 1807 Class 2 Serial Data




3 -- -- Not Used

4 BK 2050 Ground

5 BK/WH 1151 Ground

6-15 -- -- Not Used

16 OG 40 Battery Positive Voltage

data line_bcm control schematics

Documents

serial data line

body control module

loss of serial data

powertrain control module

noncommunicating module

bcm control inputs

certain body control

scan tool power ground