Computer/integrating Systems Chevrolet Cobalt I

Computer/Integrating Systems Schematic Icons Icon Icon Definition CAUTION: When performing service on or near the SIR components or the SIR wiring, the SIR system must be disabled. Refer to SIR Disabling and Enabling Zones. Failure to observe the correct procedure could cause deployment of the SIR components, personal injury, or unnecessary SIR system repairs. IMPORTANT: Twisted-pair wires provide an effective shield that helps protect sensitive electronic components from electrical interference. In order to prevent electrical interference from degrading the performance of the connected components, you must maintain the proper specification when making any repairs to the twisted-pair wires shown : The wires must be twisted a minimum of 9 turns per 31 cm (12 in) as measured anywhere along the length of the wires. The outside diameter of the twisted wires must not exceed 6.0 mm (0.25 in)

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Body Control Module (BCM) C1 Connector Part Information OEM: 15393122 Service: See Catalog 72-Way F Micro 64 (GY) Pin Wire Color Circuit No. Function 1 L-BU/BK 747 Left Rear Door Ajar Switch Signal (Sedan) 2-5 - - Not Used 6 WH 682 Door Lock Lock/Unlock Signal 7 WH 682 Door Lock Lock/Unlock Signal 8 WH 1080 Park Lamp Relay Control 9-12 - - Not Used 13 PK 849 Brake Fluid Level Sensor Signal (1) 14 L-BU 1134 Park Brake Switch Signal 15 YE 5199 Run/Crank Relay Coil Control 16 WH 193 Rear Defog Relay Control 17 D-BU 15 Right Turn Signal Lamp Supply Voltage 18 D-GN 5060 Low Speed GMLAN Serial Data 19 TN/WH 746 Right Front Door Ajar Switch Signal 20 L-GN/BK 748 Right Rear Door Ajar Switch Signal (Sedan) 21 - - Not Used 22 GY/BK 745 Left Front Door Ajar Switch Signal 23-26 - - Not Used 27-30 - - Not Used 31 OG/BK 737 Trunk Lamp Control 32 - - Not Used 33 D-GN/WH 1135 Brake Transmission Shift Interlock Solenoid Supply Voltage 34 - - Not Used 35 L-BU 14 Left Turn Signal Lamp Supply Voltage 36 D-GN 5060 Low Speed GMLAN Serial Data 37-43 - - Not Used 44 TN/WH 1969 Headlamp High Beam Relay Control 45-46 - - Not Used 47 YE 196 Windshield Wiper Motor Park Switch Signal 48-50 - - Not Used 51 D-GN 113 Windshield Wiper Switch On Signal 52-53 - - Not Used 54 YE 317 Fog Lamp Relay Coil Supply Voltage (T37) 55 OG/BK 744 Trunk Ajar Switch Signal 56 - - Not Used 57 BN 253 Trunk Release Relay Control 58-59 - - Not Used 60 TN 28 Horn Relay Control 61 BK/WH 1251 Signal Ground 62 RD/WH 1240 Battery Positive Voltage 63 GY 596 5-Volt Reference 64 BK/WH 751 Signal Ground 65 TN/WH 1704 Sensor Low Reference 66 GY/BK 1798 Low Reference (Sedan) 67 YE/BK 61 Outside Ambient Temperature Sensor Low Reference 68 WH 5075 Current Sensor Signal 69 - - Not Used 70 D-GN/WH 636 Outside Ambient Air Temperature Sensor Signal 71-72 - - Not Used

Body Control Module (BCM) C2 Connector Part Information OEM: 15393121 Service: See Catalog 72-Way F Micro 64 (GY) Pin Wire Color Circuit No. Function 1 BN/WH 2500 High Speed GMLAN Serial Data (+) (1) 2 TN/BK 2500 High Speed GMLAN Serial Data (+) (1) 3 YE 10 Headlamp Switch Signal 4 PU 524 Headlamp Dimmer Switch High Beam Signal 5 BN/WH 301 Park Lamp Switch On Signal 6-8 - - Not Used 9 WH 111 Hazard Switch Signal 10 TN 1576 Rear Compartment Lock Actuator Unlock 11 D-GN 264 Security Indicator Supply Voltage 12 TN/WH 1455 Keyless Entry Program Enable Signal 13 - - Not Used 14 TN 28 Horn Relay Control 15 WH 103 Headlamp Switch On Signal 16 OG 192 Front Fog Lamp Switch Signal (T37) 17 PU/WH 549 Headlamp Switch Headlamps Off Signal 18 - - Not Used 19 BN 2501 High Speed GMLAN Serial Data (-) (1) 20 TN 2501 High Speed GMLAN Serial Data (-) (1) 21-25 - - Not Used 26 D-GN 44 Instrument Panel Lamp Dimmer Switch Signal 27-37 - - Not Used 38 D-GN 5060 Low Speed GMLAN Serial Data 39-43 - - Not Used 44 L-GN/BK 1137 DRL Ambient Light Sensor Signal 45-46 - - Not Used 47 YE/BK 1138 DRL Ambient Light Sensor Low Reference 48-50 - - Not Used 51 BN 1356 Flash To Pass Switch Signal 52-53 - - Not Used 54 L-BU 20 Stop Lamp Supply Voltage 55 - - Not Used 56 WH 1390 Off/Run/Crank Voltage 57 GY 112 Windshield Wiper Switch Low/Pulse Signal 58 PU 719 Sensor Low Reference 59-60 - - Not Used 61 GY 1884 Cruise Control Set/Coast/Resume/Accelerate Switch Signal 62 WH/BK 1073 Ignition Key Resistor Signal 63-65 - - Not Used 66 YE/BK 1418 Left Rear Turn Signal Switch Signal 67 D-GN/WH 1419 Right Rear Turn Signal Switch Signal 68 L-BU 292 Rear Defog Switch Signal 69 L-GN 66 A/C Request Signal 70-71 - - Not Used 72 WH 193 Rear Defog Relay Control

Body Control Module (BCM) C3 Connector Part Information OEM: 15404825 Service: See Catalog 41-Way F Metri-Pack 280, 800 Series (RD) Pin Wire Color Circuit No. Function A1 TN 294 Door Lock Actuator Unlock Control (AU3) A2 TN 294 Door Lock Actuator Unlock Control (AU3) TN 294 Door Lock Actuator Unlock Control (AU3) (Sedan) A3 D-BU/WH 149 Courtesy Lamp Supply Voltage A4 GY 295 Door Lock Actuator Lock Control (AU3) (Driver) GY 295 Door Lock Actuator Lock Control (AU3) (Passenger) A5 GY 295 Door Lock Actuator Lock Control (AU3) GY 295 Door Lock Actuator Lock Control (AU3) (Sedan) A6 - - Not Used A7 BN 9 Park Lamp Supply Voltage A8 PK 339 Run/Crank Ignition 1 Voltage (UQ3) A9 YE 18 Left Rear Stop/Turn Lamp Supply Voltage A10 GY 157 Interior Lamp Control A11 - - Not Used A12 D-GN 19 Right Rear Stop/Turn Lamp Supply Voltage B1 TN 694 Driver Door Lock Actuator Unlock Control B2 - - Not Used B3 RD/WH 1240 Battery Positive Voltage RD/WH 1240 Battery Positive Voltage B4 - - Not Used B5 BN 4 Accessory Voltage (LSJ) B5 BN 4 Accessory Voltage (L61) BN 4 Accessory Voltage (L61) B6-B7 - - Not Available B8-B11 - - Not Used B12 GY 8 Instrument Panel Lamp Supply Voltage (1) (LSJ) and (J41) B12 GY 8 Instrument Panel Lamp Supply Voltage (1) (L61) GY 8 Instrument Panel Lamp Supply Voltage (1) (L61) C1-C2 - - Not Available C3 D-GN 1301 Retained Accessory Power Fuse Supply Voltage C4 - - Not Used C5 D-GN 801 Retained Accessory Power Fuse Supply Voltage C6-C7 - - Not Available C8-C11 - - Not Used C12 OG 228 Windshield Washer Pump Control D1 RD/BK 142 Battery Positive Voltage D2 - - Not Available D3 - - Not Used D4 RD/WH 840 Battery Positive Voltage D5 D-GN 801 Retained Accessory Power Fuse Supply Voltage D6 PK 739 Run/Crank Ignition 1 Voltage D7 PK 1339 Run/Crank Ignition 1 Voltage D8-D9 - - Not Used D10 RD/BK 442 Battery Positive Voltage D11 - - Not Used D12 RD/WH 242 Battery Positive Voltage

Body Control Module (BCM) C4 Connector Part Information OEM: 15356603 Service: See Catalog 68-Way F Metri-Pack 280 Series (L-GY) Pin Wire Color Circuit No. Function A1 RD/WH 640 Battery Positive Voltage (UQ3) RD/WH 640 Battery Positive Voltage (UQ3) A2-A12 - - Not Used B1 OG 228 Windshield Washer Pump Control B2-B12 - - Not Used C1 RD/WH 1440 Battery Positive Voltage C2 GY 8 Instrument Panel Lamp Supply Voltage (1) GY 8 Instrument Panel Lamp Supply Voltage (1) C3-C5 - - Not Used C6-C7 - - Not Available C8 BN 4 Accessory Voltage BN 4 Accessory Voltage (Sedan) C8 BN 4 Accessory Voltage (Coupe) (TV5) C9-C11 - - Not Used C12 RD/WH 1140 Battery Positive Voltage (UQ4) RD/WH 1140 Battery Positive Voltage (UQ4) C12 RD/WH 1140 Battery Positive Voltage (TV5) D1 RD/WH 1040 Battery Positive Voltage D2 - - Not Used D3 YE 5199 Run/Crank Relay Coil Control D4 BN 141 Run Ignition 3 Voltage D5 - - Not Used D6-D7 - - Not Available D8-D12 - - Not Used E1 RD/WH 140 Battery Positive Voltage E2-E5 - - Not Used E6 PK 439 Run/Crank Ignition 1 Voltage PK 439 Run/Crank Ignition 1 Voltage (Coupe) (TV5) E7-E11 - - Not Used E12 BK 651 Ground F1 RD/WH 1540 Battery Positive Voltage F2 GY 8 Instrument Panel Lamp Supply Voltage (1) F3 GY 8 Instrument Panel Lamp Supply Voltage (1) GY 8 Instrument Panel Lamp Supply Voltage (1) F4 PK 339 Run/Crank Ignition 1 Voltage PK 339 Run/Crank Ignition 1 Voltage F5 PK 339 Run/Crank Ignition 1 Voltage F6 PK 339 Run/Crank Ignition 1 Voltage F7-F8 - - Not Used F9 PK 1539 Run/Crank Ignition 1 Voltage PK 1539 Run/Crank Ignition 1 Voltage F10-F12 - - Not Used

Data Link Connector (DLC) Connector Part Information OEM: 15317575 Service: See Catalog 16-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function 1 D-GN 5060 Low Speed GMLAN Serial Data 2 D-GN 1049 PCM Class 2 Serial Data (LSJ) 3 - - Not Used 4 BK 550 Ground 5 BK/WH 1051 Signal Ground 6 TN/BK 2500 High Speed GMLAN Serial Data (+) (1) 7-13 - - Not Used 14 TN 2501 High Speed GMLAN Serial Data (-) (1) 15 - - Not Used 16 RD/WH 40 Battery Positive Voltage

Begin the system diagnosis with Diagnostic System Check - Vehicle in Vehicle DTC Information. The Diagnostic System Check - Vehicle will provide the following information

1. The identification of the control modules which are not communicating.
2. The identification of any stored diagnostic trouble codes (DTCs) and their status.

The use of the Diagnostic System Check - Vehicle will identify the correct procedures to begin vehicle diagnosis. These must be performed before system DTC or symptom diagnosis.

Scan Tool Output Controls

BCM

Scan Tool Data List

Vehicle Control Systems Data

Circuit Description

The internal fault detection is handled inside the control module. No external circuits are involved.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC B1000 Electronic Control Unit (ECU) Performance

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B1000

Conditions for Running the DTC

The module runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

Conditions for Setting the DTC

The module has detected an internal malfunction.

Action Taken When the DTC Sets

The module refuses all additional inputs.

Conditions for Clearing the DTC

1. A current DTC clears when the malfunction is no longer present in all modules.
2. A history DTC clears in all of the modules except the sensing and diagnostic module (SDM), when the ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
3. If the code is set in the SDM it will never clear and the Air Bag indicator will remain illuminated.

Diagnostic Aids

1. This DTC may be stored as a history DTC without affecting the operation of a module, except the SDM. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module. Attempt to clear the code from any module except if the code is set in the SDM.
2. If this DTC is retrieved as both a current and history DTC, replace the module.
3. If the code is set as current or history in the SDM, the SDM must be replaced.

DTC B1000

The body control module (BCM) stores the last 4 digits of the sensing and diagnostic module (SDM) part number, information also called restraints ID. After the BCM is reprogrammed, the restraints ID is set to zero. A restraints ID relearn needs to be performed for the BCM. For more information on this procedure, refer to Body Control Module (BCM) Programming/RPO Configuration .

This diagnostic procedure supports the following DTC

DTC B1001 Option Configuration Error

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B1001

Battery voltage is between 9-16 volts and data link communications operate normally.

The restraints ID value stored in the BCM memory is zero.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DTC B1001

The internal fault detection is handled inside the control module. No external circuits are involved.

This diagnostic procedure supports the following DTC

DTC B1004 Keep Alive Memory (KAM) Reset

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B1004

The module microprocessor must be active/awake.

This DTC indicates the KAM in the module has been reset. It is a normal occurrence when battery positive voltage or ground is removed from the module, such as a battery disconnect.

The microprocessor reverts back to the base programmed critical operating data until new data is learned and stored in KAM.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

DTC B1004

The electrically erasable programmable read-only memory (EEPROM) check sum error detection is handled inside the control module. No external circuits are involved.

This diagnostic procedure supports the following DTC

DTC B1009 EEPROM Checksum Mismatch

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B1009

The module runs the program to detect an EEPROM checksum error after each wake-up. The only requirements are battery positive voltage and ground. This program runs even if the voltage is out of the valid operating range.

The module retains an inverse copy of the digital value stored in certain blocks of memory in the EEPROM. The module then reads the information from those certain blocks and adds the stored inverse value to the current value. If they do not equal 0, the module sets the DTC.

The module reverts to base operation values programed for those blocks of data that have failed the check sum test. The blocks of data that have not failed the check sum test are not affected.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

DTC B1009

The body control module (BCM) monitors the ignition 1 signal from the ignition switch. When the vehicle operator places the ignition switch in the RUN or CRANK position, the switch supplies B+ to the BCM ignition 1 input terminal. If this circuit becomes shorted to B+, ground or the circuit opens, DTC B1370 will set.

This diagnostic procedure supports the following DTC

DTC B1370 Device Ignition 1 Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B1370

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

1. The BCM detects a short to ground in the ignition 1 voltage circuit when the ignition switch is in RUN or CRANK.
2. The BCM detects a short to battery or an open in the ignition 1 voltage circuit when the switch is in the OFF position.
3. Any of the conditions above must be present for more than 10 seconds.

1. The BCM stores DTC to memory.
2. The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the GMLAN serial data communications circuits.
3. The other modules on the vehicle operate in a fail-safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the GMLAN serial data communications circuits.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

A history DTC may be caused by an intermittent short or open in the ignition 1 circuit. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 3: This tests the ignition switch for a short circuit between the 12-volt reference supply circuit and the ignition 1 circuit in the OFF position.
2. 4: This tests the wiring of the ignition 1 circuit for a short to ground or voltage.
3. 5: This tests the ignition switch for a closed circuit between the ignition switch 12-volt reference supply circuit and the ignition 1 circuit in the Run and Crank switch positions. Care must be taken as the engine may crank during this test.

DTC B1370

The body control module (BCM) monitors the ACCESSORY signal from the ignition switch. When the vehicle operator places the ignition switch in the Accessory or Run position, the switch supplies B+ to the BCM ACCESSORY input terminal. If this circuit becomes shorted to B+, ground or the circuit opens, DTC B1380 will set.

This diagnostic procedure supports the following DTC

DTC B1380 Device Ignition ACCESSORY Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B1380

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

1. The BCM detects a short to ground in the ACCESSORY voltage circuit when the ignition switch is in RUN or CRANK.
2. The BCM detects a short to battery or an open in the ACCESSORY voltage circuit when the switch is in the OFF position.
3. Any of the conditions above must be present for more than 10 seconds.

1. The BCM stores DTC to memory.
2. The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the GMLAN serial data communications circuits.
3. The other modules on the vehicle operate in a fail-safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the GMLAN serial data communications circuits.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

A history DTC may be caused by an intermittent short or open in the ACCESSORY circuit. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

The numbers below refer to the step numbers on the diagnostic table.

1. 3: This tests the ignition switch for a short circuit between the 12-volt reference supply circuit and the ACCESSORY circuit in the OFF position.
2. 4: This tests the wiring of the ACCESSORY circuit for a short to ground or voltage.
3. 5: This tests the ignition switch for a closed circuit between the ignition switch 12-volt reference supply circuit and the ACCESSORY circuit in the Run and Accessory switch positions. Care must be taken as the engine may crank during this test.

DTC B1380

The body control module (BCM) monitors the OFF/RUN/CRANK signal from the ignition switch. The signal is zero when there is no key in the ignition cylinder. The signal is at the 12-volt reference level when a key is placed into the ignition cylinder. When the vehicle operator places the ignition switch in the Run position, the switch supplies +5 volts to the BCM OFF/RUN/CRANK input terminal. During a crank event, the +5 volt signal is passed through an internal resistor in the ignition switch for discrimination of the crank command. If the OFF/RUN/CRANK circuit becomes shorted to B+, ground or the circuit opens, DTC B1441 will set.

This diagnostic procedure supports the following DTC

DTC B1441 Device Ignition OFF, RUN and CRANK Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B1441

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

1. The BCM detects a short to ground in the OFF/RUN/CRANK voltage circuit when the ignition switch is in RUN or CRANK.
2. The BCM detects a short to battery or an open in the OFF/RUN/CRANK circuit.
3. Any of the conditions above must be present for more than 10 seconds.

1. The BCM stores DTC to memory.
2. The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the GMLAN serial data communications circuits.
3. The other modules on the vehicle operate in a fail-safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the GMLAN serial data communications circuits.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

A history DTC may be caused by an intermittent short or open in the OFF/RUN/CRANK circuit or the +5-volt reference circuit. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

The numbers below refer to the step numbers on the diagnostic table.

1. 3: This tests the OFF/RUN/CRANK circuit for a short circuit to B+ and ground. Because of the control over powermoding this step must be performed with the switch in the OFF position. Any shorts to ground during this step could be a short to a voltage circuit that is only powered in Run or Accessory. The loads on these circuits would indicate a short to ground, but the cause would have to be traced thorough the OFF/RUN/CRANK circuit and repaired.
2. 4: This tests the ignition switch contacts of the OFF/RUN/CRANK circuit for merit.
3. 5: This tests the OFF/RUN/CRANK, +5-volt and +12-volt circuits for an open.

DTC B1441

The internal fault detection is handled inside the control module. No external circuits are involved. DTC C0550 is set when an internal malfunction takes place within the control module.

This diagnostic procedure supports the following DTC

DTC C0550 Electronic Control Unit (ECU) Performance

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC C0550

The microprocessor runs a diagnostic program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

1. The control module detects an internal write malfunction.
2. The control module detects an internal checksum malfunction.

If equipped, the following module specific actions may occur

1. The antilock brake system (ABS) indicator turns ON.
2. The BRAKE warning indicator turns ON.
3. The electronic brake control module (EBCM) disables the ABS/dynamic rear proportion (DRP)/traction control system (TCS).
4. The driver information center (DIC) displays the power steering warning message No Steering Assist.
5. The TCS indicator turns ON.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and a history DTC, replace the module.
3. If this DTC continues to set intermittently, replace the module.

DTC C0550

The Run/Crank relay is controlled by the body control module (BCM). The Run/Crank relay contacts are supplied a hot at all times from the fuse block underhood. The relay supplies power to several components when the vehicle is in the RUN or CRANK power mode. This signal is labeled Ignition 1. When the ignition switch is placed in the RUN or CRANK position, the BCM will receive a Run/Crank signal from the ignition switch and turn ON the Run/Crank relay. When the ignition switch is in the OFF position, the BCM will turn OFF the Run/Crank relay. The powertrain control module (PCM) compares the Run/Crank relay output signal with the BCM Class 2 serial data power mode message. If the ignition 1 voltage signal and the power mode message do not match for an allotted time, the PCM will disable the fuel injectors and DTC P2535 will set.

This diagnostic procedure supports the following DTC

DTC P2535 Ignition 1 Switch Circuit High Voltage

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC P2535

1. The vehicle is in PARK or NEUTRAL.
2. The ignition switch is OFF.

The ignition 1 voltage signal is higher than normal for more than 7 seconds.

1. The control module stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
4. The driver information center, if equipped, may display a message.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear the DTC with a scan tool.

DTC P2535

Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. Each module on GMLAN network maintains a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255 the controller removes itself from the network and a DTC U0001 will be set.

This diagnostic procedure supports the following DTC

DTC U0001 High Speed CAN Communication Bus

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC U0001

1. Voltage supplied to the module is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.

A certain number of no valid transmitted messages on the GMLAN serial data circuits are detected by the module.

1. The module suspends all message transmission.
2. The module uses default values for all parameters received on the GMLAN serial data circuits.
3. The module inhibits the setting of all other GMLAN communication DTCs.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC cannot be retrieved with a current status. Diagnosis of current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with GMLAN Device. Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with) .
2. An intermittent condition is likely to be caused by a short on the GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with GMLAN Device procedure in order to isolate an intermittent condition. Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with) .

Control modules connected to the high and low speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the control modules. The control modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

DTC U0100 00: Lost Communication with Engine Control Module (ECM)

DTC U0101 00: Lost Communication with Transmission Control Module (TCM)

DTC U0107 00: Lost Communication with Throttle Actuator Control Module

DTC U0121 00: Lost Communication with Electronic Brake Control Module (EBCM)

DTC U0140 00: Lost Communication with Body Control Module

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

Diagnostic Fault Information

DTC U0100-U02FF

1. The system voltage is between 9-16 V.
2. The vehicle power mode master requires serial data communication to occur.

A supervised periodic message that includes the transmitter module availability has not been received.

The control modules is never signaled. Therefore, the specific subsystems will not function

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios

1. A control module on the data communication circuit was disconnected while the communication circuit is awake.
2. Power to one or more control modules was interrupted during diagnosis.
3. A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
4. Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
5. If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.

Use the DTC Descriptor list above to determine the control module which is not communicating.

Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.

Use Data Link References to determine if the control module uses high or low speed GMLAN serial data communications

Some control modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no control module output voltage circuit is shorted to ground before replacing the control module.

This diagnostic can be used for any control module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that control module.

Circuit/System Testing

Note. Use the schematic to identify the following: Control modules the vehicle is equipped with Control module locations on the low and high speed GMLAN serial data circuits The control module's ground, B+, ignition, and serial data circuit terminals

1. Using the DTC Descriptor above, determine the control module that is not communicating and should be tested.
2. Ignition OFF, disconnect the harness connector of the control module that is not communicating.
3. Test for less than 10 E between each ground circuit terminal and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
4. If equipped, ignition ON, verify that a test lamp illuminates between each B+ circuit terminal and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
5. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.
6. Ignition OFF for 60 seconds, test for less than 5 E between the serial data circuit terminals and the appropriate data link connector (DLC) terminal listed below: Class 2 serial data. circuit terminal 2 Low speed GMLAN serial data terminal 1 High speed GMLAN serial data terminal 6 or 14 If greater than the specified range, test the serial data circuit for an open/high resistance between the non-communicating control module and the control module setting the DTC or a serial data splice pack.
7. If all circuits test normal, replace the control module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

1. GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs
2. Control Module References for control module replacement, programming and setup

The powertrain control module (PCM) on this vehicle uses the class 2 serial data buss strictly for diagnostic purposes. When the PCM detects one of the following conditions on the class 2 serial data circuit for approximately 3 seconds, the setting of all other class 2 serial communication DTCs is inhibited and a DTC will set.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC U1300 Class 2 Data Link Low
2. DTC U1301 Class 2 Data Link High
3. DTC U1305 Class 2 Data Link Low or High

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC U1300, U1301, or U1305

Conditions for Running the DTCs

1. Voltage supplied to the module is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.

Conditions for Setting the DTCs

1. No valid messages are detected on the class 2 serial data circuit.
2. The voltage level detected on the class 2 serial data circuit is in one of the following conditions: High Low
3. The above conditions are met for approximately 3 seconds.

Action Taken When the DTCs Sets

The module uses default values for all parameters received on the class 2 serial data circuit.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

The numbers below refer to the step numbers on the diagnostic table.

1. 3: If you can communicate with the PCM, the malfunction may be an intermittent short to voltage or ground in the wiring of the class 2 serial data circuit.
2. 5: If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
3. 6: The communication malfunction may have prevented diagnosis of the customer complaint.

DTC U1300, U1301, or U1305

The GMLAN serial data circuits are controller area network (CAN) high speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. On this vehicle there are 2 utterly different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. Refer to Data Link Communications Description and Operation for the complete description of these buses. The GMLAN serial data circuits also communicate directly to the DLC connector. Messages are interpreted by the externally connected CAN module which acts as a transceiver for the scan tool.

Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules. All the modules on the GMLAN networks, maintain a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255, the controller removes itself from the network and DTC U2100 will result.

This diagnostic procedure supports the following DTC

DTC U2100 Controller Area Network (CAN) Bus Communication

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC U2100

1. Supply voltage to the modules are in the normal operating range.
2. The vehicle is in the RUN power mode.

The module setting the DTC has attempted to establish communications on the GMLAN circuits for more than 7 times.

1. The module suspends all message transmission.
2. The module uses default values for all parameters received on the serial data circuits.
3. The module inhibits the setting of all other communication DTCs.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC cannot be retrieved with a current status. Diagnosis of a current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with High Speed or Low Speed GMLAN Device. Refer to «Data Link References»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__data-link-references) for the correct procedure for the specific modules.
2. An intermittent condition is likely to be caused by a short on the GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with High Speed or Low Speed GMLAN Device procedure in order to isolate an intermittent condition. Refer to «Data Link References»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__data-link-references) for the correct procedure for the specific modules.

Modules connected to the GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have programmed information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are also supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module.

DTC U2103 will set when fewer modules are detected on the buss before the modules can learn the other module's IDs. If the communication buss is opened, or if the module's power supply is lost when the vehicle is in the OFF power mode, and then placed in the RUN power mode, U2103 will set in specific modules.

This diagnostic procedure supports the following DTC

DTC U2103 Fewer Controllers On Than Programmed

When more than one Fewer Controllers On than Programmed DTC is set in either one module or in several modules, diagnose the DTCs in the following order

1. Current DTCs before history DTCs unless told otherwise in the diagnostic table.
2. The DTC which is reported the most times.

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC U2103

1. Voltage supplied to the modules is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.
3. The DTC U2100 does not have a current status.

A supervised periodic message that includes the transmitter module availability has not been received.

The module uses a default value for the missing parameter.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. A poor connection at the inoperative module may cause this code to set.
2. An improperly powered module may cause this code to set.

The numbers below refer to the step numbers on the diagnostic table

1. 3: If the body control module (BCM) will not power up, the vehicle cannot establish the correct power mode. This step tests for the correct power supply conditions for the BCM.
2. 4: If DTC U2103 is set as history and you can communicate with the suspect module, the malfunction is an intermittent communication buss, power supply, ground or internal module connection.
3. 5: This step tests for the correct power supply conditions of the suspect module or modules.
4. 6: This step identifies which of the GMLAN busses the module or modules use for communication. Use the «Data Link References»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__data-link-references) for identifying the correct buss to analyze.
5. 11: The module which was not communicating due to an open in the GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.
6. 20: The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

DTC U2103

Modules connected to the GMLAN serial data circuits monitor for serial data communications, during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have programmed information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are also supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module. When a message that indicates the availability of the transmitter module is not received, the receiver module sets a DTC 21xx where xx is equal to the 2-digit identification number of the transmitter module.

The DTC descriptors listed below provide a method for determining which module is not communicating. A module with a GMLAN serial data circuit malfunction or which loses power during the 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 cannot communicate.

This diagnostic procedure supports the following DTCs

1. DTC U2105 Lost Communications With Engine Control System
2. DTC U2106 Lost Communications With Transmission Control System
3. DTC U2107 Lost Communications With Body Control System
4. DTC U2108 Lost Communications With ABS/TCS Control System
5. DTC U2109 Lost Communications With Powertrain Multiple Control System
6. DTC U2111 Lost Communications With Steering Control System
7. DTC U2113 Lost Communications With Sensing Diagnostic Module (SDM)
8. DTC U2116 Lost Communications With Instrument Panel Cluster (IPC)
9. DTC U2122 Lost Communications With Radio
10. DTC U2125 Lost Communication With Mobile Communications Control Systems
11. DTC U2127 Lost Communications With Front HVAC
12. DTC U2137 Lost Communications With Vehicle Theft Deterrent (VTD)
13. DTC U2171 Lost Communications With DVD Player
14. DTC U2172 Lost Communications With Digital Radio Receiver

When more than one Loss of Communication DTC is set in either one module or in several modules, diagnose the DTCs in the following order

1. Current DTCs before history DTCs unless told otherwise in the diagnostic table.
2. The DTC which is reported the most times.

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC U2105-U2199

1. Voltage supplied to the modules is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.
3. DTC U2100 does not have a current status.

A supervised periodic message that includes the transmitter module availability has not been received.

The module uses a default value for the missing parameter.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. A poor connection at the inoperative module may cause this code to set.
2. An improperly powered module may cause this code to set.

The numbers below refer to the step numbers on the diagnostic table

1. 3: Non ABS equipped vehicles may set a DTC U2108 falsely. If this is the case there is no malfunction with this system.
2. 5: If the body control module (BCM) will not power up, the vehicle cannot establish the correct power mode. This step test for the correct power supply conditions for the BCM.
3. 6: If DTC U2105 to U2177 are set as history and you can communicate with the suspect module, the malfunction is an intermittent communication buss, power supply, ground or internal module connection.
4. 7: This step tests for the correct power supply conditions of the suspect module or modules.
5. 8: This step identifies which of the GMLAN busses the module or modules use for communication. Use the «Data Link References»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__data-link-references) for identifying the correct buss to analyze.
6. 13: The module which was not communicating due to an open in the GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.
7. 14: The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

DTC U2105-U2199

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/cobalt/i-2004-2010/remont/oem-general-information/#vehicle-dtc-information) in Vehicle DTC Information before using the symptom tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data links.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to: «Data Link Communications Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems) «Body Control System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__body-control-system-description-and-operation) «Retained Accessory Power (RAP) Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems)

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the systems. Refer to «Checking Aftermarket Accessories»(/chevrolet/cobalt/i-2004-2010/remont/electrical-component-locations/#wiring-systems-electrical-power-management__checking-aftermarket-accessories) in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Scan Tool Does Not Power Up»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems)
2. «Scan Tool Does Not Communicate with Class 2 Device»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems)
3. «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with)
4. «Scan Tool Does Not Communicate with Low Speed GMLAN Device»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with)
5. «Retained Accessory Power (RAP) On After Timeout»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__retained-accessory-power-rap-on-after)
6. «Retained Accessory Power (RAP) Inoperative»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__retained-accessory-power-rap-inoperative)

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

1. Scan tool power battery positive voltage at terminal 16
2. Scan tool power ground at terminal 4
3. Common signal ground at terminal 5

The scan tool will power up with the ignition OFF. Some modules, however, will not communicate unless the ignition is ON and the power mode master (PMM) module sends the appropriate power mode message.

The number below refers to the step number on the diagnostic table.

1. 4: If the battery positive voltage and ground circuits of the DLC are functioning properly. The malfunction must be due to the scan tool.

Scan Tool Does Not Power Up

The powertrain control module (PCM) is connected to the class 2 serial data circuit. The class 2 serial data circuit is used for diagnostic purposes only in this vehicle. Connecting a scan tool to the data link connector (DLC) allows communication with the PCM for diagnostic purposes. DTCs may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

The PCM is the only module on the class 2 serial data buss on this vehicle. The most likely cause of the buss failure will be a short or open.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: A partial loss or intermittent loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.
2. 10: If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
3. 11: The communication concern may have prevented diagnosis of the customer complaint.

Scan Tool Does Not Communicate with Class 2 Device

Scan Tool Does Not Communicate with High Speed GMLAN Device

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications on the high speed GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition a DTC U0001 or U2100 will be set. These DTCs can be retrieved as history only.

The high speed GMLAN serial data buss uses two 120 ohms terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is connected at the data link connector (DLC) end of the link and the other is at the engine management module, engine control module (ECM) or powertrain control module (PCM), end of the link. The DLC terminating resistor resides internally in the body control module (BCM). When testing for a short between high speed GMLAN (+) and (-) with the engine management module removed, a reading off 120 ohms is normal. However, to completely analyze the buss the BCM should be temporally removed when testing for shorts between the high speed GMLAN (+) and (-) while also making sure that all modules and the scan tool are disconnected from the buss. A normal reading across the high speed GMLAN buss with the terminating resistor at the DLC remove and all module and scan tool disconnected is infinite ohms. Make certain to reconnect the BCM after testing, it is necessary for proper vehicle powermoding.

The engine will not start when there is a total malfunction of the high speed GMLAN serial data circuits while the engine is not running. The following conditions may cause a total loss of high speed GMLAN data communication

1. A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
2. Any of the high speed GMLAN serial data circuits shorted to ground or voltage
3. A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits

The numbers below refer to the step numbers on the diagnostic table.

1. 2: A partial malfunction in the high speed GMLAN serial data circuits uses a different procedure from a total malfunction of the high speed GMLAN data circuits. Refer to «Data Link References»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__data-link-references) to identify which modules communicate on the high speed GMLAN serial data circuits.
2. 3: The DTC U2100 may be retrieved with a history status, but is not the cause of the present condition.
3. 8: Data link connector terminals 6 and 14 provide the connection to the GMLAN serial data high circuit and the GMLAN serial data low circuit respectively.
4. 17: The communication malfunction may have prevented diagnosis of the customer complaint.

Scan Tool Does Not Communicate with High Speed GMLAN Device

Scan Tool Does Not Communicate with Low Speed GMLAN Device

Modules connected to the low speed GMLAN serial data circuits monitor for serial data communications on the low speed GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition, DTC U2100 will be set. These DTCs can be retrieved as history only.

The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuits while the engine is not running. The following conditions may cause a total loss of low speed GMLAN data communication

1. Any of the low speed GMLAN serial data circuits shorted to ground or voltage
2. A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuits

The numbers below refer to the step numbers on the diagnostic table.

1. 2: A partial malfunction in the low speed GMLAN serial data circuits uses a different procedure from a total malfunction of the low speed GMLAN data circuits. Refer to «Data Link References»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems__data-link-references) to identify which modules communicate on the low speed GMLAN serial data circuits.
2. 3: The DTC U2100 may be retrieved with a history status, but is not the cause of the present condition.
3. 7: Data link connector terminal 1 provides the connection to the GMLAN serial data low circuit and the GMLAN serial data low circuit respectively.
4. 16: The communication malfunction may have prevented diagnosis of the customer complaint.

Scan Tool Does Not Communicate with Low Speed GMLAN Device

Normal vehicle serial data communications and the control modules operations will not begin until the system power mode has been identified. Discrete wires from the ignition switch contacts are monitored by a module which acts as the power mode master (PMM) in order to determine the correct power mode. The module which is the PMM communicates the system power mode to all modules on the serial data lines. Refer to Body Control System Description and Operation to identify which module is the PMM and the applicable power mode look up table.

The numbers below refer to the step numbers on the diagnostic table.

1. 6: This step tests for battery voltage on the incorrect signal circuits.
2. 7: This step tests for no battery voltage on the required signal circuits.
3. 8: If any ignition switch parameters that should be inactive in the present ignition switch position are active, 2 ignition switch signal circuits may be shorted together.
4. 9: This step eliminates open circuits as the cause of the malfunction.

Power Mode Mismatch

Retained Accessory Power (RAP) On After Timeout

Retained Accessory Power (RAP) On After Timeout

Retained Accessory Power (RAP) Inoperative

Retained Accessory Power (RAP) Inoperative

Control Module References

Control Module References

Data Link References

This table identifies which serial data link that a particular module uses for in-vehicle data transmission. Some modules may use more than one data link to communicate. Some modules may have multiple communication circuits passing through them without actively communicating on that data link. This table is used to assist in correcting a communication malfunction. For the description and operation of these serial data communication circuits, refer to Data Link Communications Description and Operation .

Data Link References

Scheme 11

Body Control Module Replacement

Body Control Module (BCM) Programming/RPO Configuration

1. A new body control module (BCM) must be programmed with the proper regular production option (RPO) configurations. The BCM stores the information regarding the vehicle options and if the BCM is not properly configured with the correct RPO codes, the BCM will not control all of the features properly. The Tech 2 software will automatically prompt you with the RPO available for the vehicle. Ensure that the following conditions exist in order to prepare for BCM programming: The battery is fully charged. The ignition switch is in the ON position. The data link connector (DLC) is accessible. All disconnected modules and devices are reconnected before programming.
2. To setup a new BCM, access the Vehicle Control Systems in Computer/Integrating Systems menu on the scan tool to program the BCM. Select Module Replacement/Setup and follow the instructions on the scan tool.
3. If the BCM fails to accept the program, perform the following steps: Inspect all BCM connections. Verify that the scan tool has the latest software version.

Passkey 3 Programming Procedures

Perform the Passkey 3 Programming Procedure if any of the following components have been replaced

1. The BCM
2. The powertrain control module (PCM) Refer to «Programming Theft Deterrent System Components»(/chevrolet/cobalt/i-2004-2010/remont/door-locks-anti-theft-systems/#theft-deterrent-system) in Theft Deterrent for the proper procedure.

1. Turn the ignition OFF for 10 seconds.
2. Connect the scan tool to the data link connector.
3. Turn the ignition ON with the engine OFF.
4. Use the scan tool in order to retrieve history DTCs from all modules.
5. Clear all history DTCs.

The communication among control modules is performed through the GMLAN high speed serial data circuit and the GMLAN low speed serial data circuit. The modules that need real time communication are attached to the high speed GMLAN network. The body control module (BCM) is the gateway between the networks. The purpose of the gateway is to translate serial data messages between the GMLAN high speed buss and the GMLAN low speed buss. The gateway will interact with each network according to that network's transmission protocol. Refer to Body Control System Description and Operation for more information about the gateway.

The powertrain control module (PCM) on this vehicle, uses a class 2 serial data buss. The class 2 buss is only used for diagnostics and the service programming system (SPS). During normal vehicle operations, there is no communications over the class 2 serial data buss. Normal vehicle operational messaging for the PCM is sent over the PCMs GMLAN high speed serial data buss.

GMLAN High Speed Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the high speed GMLAN serial data circuit. The serial data is transmitted on 2 twisted wires that allow speed up to 500 Kb/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the powertrain control module (PCM) or engine control module (ECM) depending on regular production option (RPO) and the other is internal to the body control module (BCM). The BCM is considered the DLC termination point of the link and the engine management controller is the other end of the link. The resistors are used to reduce noise on the High Speed GMLAN buss during normal vehicle operation. The high speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level. The idle level, which is approximately 2.5 volts, is considered recessive transmitted data and is interpreted as a logic 1. Driving the lines to their extremes, adds one volt to the high speed GMLAN serial data bus (+) and subtracts one volt from the high speed GMLAN serial data bus (-) wire. This dominant state is interpreted as a logic 0. GMLAN network management supports selective start up and is based on virtual networks. A virtual network is a collection of signals started in response to a vehicle event. The starting of a virtual network signifies that a particular aspect of the vehicles functionality has been requested. A virtual network is supported by virtual devices, which represents a collection of signals owned by a single physical device. So, any physical device can have one or more virtual devices. The signal supervision is the process of determining whether an expected signal is being received or not. Failsofting is the ability to substitute a signal with a default value or a default algorithm, in the absence of a valid signal. Some messages are also interpreted as a heartbeat of a virtual device. If such a signal is lost, the application will set a no communication code against the respective virtual device. This code is mapped on the Tech 2 screen as a code against the physical device. Note: a loss of serial data DTC does not represent a failure of the module that the code is set in.

GMLAN Low Speed Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the low speed GMLAN serial data circuit. The serial data is transmitted over a single wire to the appropriate control modules. The transmission speed for GMLAN low speed is up to 83.33 Kb/s. Under normal vehicle operating conditions, the speed of the buss is 33.33 Kb/s. This protocol produces a simple pules train sent out over the GMLAN low speed serial data bus. When a module pulls the buss high, 5 volts, this creates a dominant logic state or 0 on the buss. When the buss is pulled low 0 volts, it is translated as a recessive logic state or 1. To wake the control modules connected to the GMLAN low speed serial data buss, a high voltage wake up pulse is sent out over the buss, the voltage level of the pules is +10 volts. Modules connected to the GMLAN low speed buss can be part of a virtual network as described in the previous paragraph. The modules on the GMLAN low speed serial data buss are connected to the buss in a parallel configuration.

Class 2 Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the class 2 serial data circuit. Class 2 serial data is transmitted on a single wire at an average of 10.4 Kbps. The bus is active at 7 volts nominal and inactive at ground potential. When the ignition switch is in RUN, and a scan tool is connected to the DLC, the powertrain control module (PCM) will start communicating diagnostic information over the class 2 serial data circuit.

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

1. Pin 1 GMLAN low speed communications terminal
2. Pin 2 Class 2 signal terminal
3. Pin 4 Scan tool power ground terminal
4. Pin 5 Common signal ground terminal
5. Pin 6 High speed GMLAN serial data bus (+) terminal
6. Pin 14 High speed GMLAN serial data bus (-) terminal
7. Pin 16 Scan tool power, battery positive voltage terminal

Class 2 Serial Data Usage

The class 2 serial data communications circuit on this vehicle is only used for powertrain control module (PCM) diagnostics and PCM service programming system (SPS) programming.

Serial Data Reference

The scan tool communicates over the various busses on the vehicle. When a scan tool is installed on a vehicle, the scan tool will try to communicate with every module that could be optioned into the vehicle. If an option is not installed on the vehicle, the scan tool will display No Comm for that options control module. In order to avert misdiagnoses of No Communication with a specific module, refer to Data Link References for a list of modules, the busses they communicate with, and the RPO codes for a specific module.

Body Control System Description and Operation

The body control module (BCM) has a bussed electrical center integrated into the housing. Body control relays and fuses are installed directly on the BCM, which simplifies wiring and junction blocks on the vehicle. The body control system consists of the BCM and its associated controls. Battery positive voltage is provided to the BCM from IBCM BATT 1 fuse and the IBCM BATT 2 fuse in the underhood fuse block. The module grounds are wired to ground G201, G203 and G305. The BCM is wired to the GMLAN High speed serial data buss, and the GMLAN Low speed serial data buss, as well as discrete input and output terminals to control the functions of the vehicle's body.

Serial Data Gateway

The body control module (BCM) in this vehicle functions as a translator between the High and Low speed GMLAN busses. The 2 communication protocols use the BCM to translate communicated serial data messages between the control modules over the 2 serial data busses.

Power Mode Master

This vehicles BCM functions as the Power Mode Master (PMM). Refer to Power Mode Description and Operation for a complete description of power mode functions.

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. The BCM functions include the following

1. A/C compressor request-Refer to «Air Temperature Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual__air-temperature-description-and-operation) in HVAC Systems - Manual.
2. A/C cooling fan-Refer to «Air Delivery Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/manual-hvac-system/#hvac-systems-manual__air-delivery-description-and-operation) in HVAC Systems - Manual.
3. Battery rundown protection (inadvertent power) - Refer to «Interior Lighting Systems Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/exterior-lights/#lighting-systems) in Lighting Systems.
4. Bulb check-Refer to «Instrument Panel Cluster (IPC) Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages, and Console.
5. Chimes-Refer to «Indicator/Warning Message Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console__indicatorwarning-message-description-and-operation) in Instrument Panel, Gages, and Console. Check gages Door ajar warning Headlamps ON Key-in-ignition Oil reset Park brake warning Seat belt not fastened Turn signal ON
6. Door lock interface - Refer to «Power Door Locks Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/door-locks-anti-theft-systems/#door-system-mirror-system-window-system) in Doors.
7. Electronic power steering (EPS)- Refer to «Power Steering System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/manual-power-steering/#power-steering-system) in Power Steering System.
8. Engine coolant level sensing - Refer to «Cooling System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/cooling-system-mechanical/#engine-cooling-system) in Engine Cooling.
9. Exterior and interior lighting control - Refer to «Exterior Lighting Systems Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/exterior-lights/#lighting-systems) in Lighting Systems. Automatic lighting control Daytime running lamps (DRL) Fog lamps Park brake lights Turn hazard lamps
10. Gage control-Refer to «Instrument Panel Cluster (IPC) Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages, and Console.
11. Horn interface-Refer to «Horns System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/horns/#horn-system) in Horns.
12. Instrument cluster indicator control-Refer to «Instrument Panel Cluster (IPC) Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages, and Console.
13. Interior lighting-Refer to «Interior Lighting Systems Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/exterior-lights/#lighting-systems) in Lighting Systems.
14. Key-in-ignition sensing-Refer to «Indicator/Warning Message Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console__indicatorwarning-message-description-and-operation) in Instrument Panel, Gages, and Console.
15. Parking brake state sensing-Refer to «Brake Warning System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/mechanical-hydraulic/#hydraulic-brake-system) in Hydraulic Brakes.
16. Retained accessory power (RAP) - Refer to «Retained Accessory Power (RAP) Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/communication-devices/#computerintegrating-systems) .
17. Rear compartment interface - Refer to «Power Door Locks Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/door-locks-anti-theft-systems/#door-system-mirror-system-window-system) in Doors.
18. Rear defogger - Refer to «Rear Window Defogger Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/heated-glassdefoggers/#stationary-windows) in Stationary Windows.
19. Remote function control - Refer to «Keyless Entry System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/door-locks-anti-theft-systems/#keyless-entry-system) in Keyless Entry.
20. Seat belt use sensing-Refer to «Seat Belt System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/restraints-control-systems/#seat-belt-system) in Seat Belts.
21. Content theft deterrent-Refer to «Theft Systems Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/door-locks-anti-theft-systems/#theft-deterrent-system) in Theft Deterrent.
22. Vehicle theft deterrent-Refer to «Vehicle Theft Deterrent (VTD) Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/door-locks-anti-theft-systems/#theft-deterrent-system) in Theft Deterrent.
23. Washer solvent level sensing-Refer to «Wiper/Washer System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/wiperwasher-systems/#wiper-system-washer-system) in Wipers/Washer Systems.
24. Wiper/washer-Refer to «Wiper/Washer System Description and Operation»(/chevrolet/cobalt/i-2004-2010/remont/wiperwasher-systems/#wiper-system-washer-system) in Wipers/Washer Systems.

Power Mode Description and Operation

Power to many of this vehicle's circuits are controlled by the module that is designated the Power Mode Master (PMM). This vehicle's PMM is the Body Control Module (BCM). The PMM controls which power mode (Run, Accessory, Crank, Retained Accessory Power, or Off) is active.

Serial Data Power Mode Master

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 PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the Serial Data circuits. The 3-wire Ignition Switch table below illustrates the state of these inputs in correspondence to the ignition switch position

3-Wire Ignition Switch

Relay Controlled Power Mode

The body control module (BCM) uses the discrete ignition switch inputs Off/Run/Crank, Accessory, and ignition 1, to distinguish the correct power mode. The ignition 1 circuit is also routed to the Run/Crank relay for relay controlled power feeds during the appropriate power mode. The BCM, after determining the desired power mode, will activate the appropriate relays for that power mode.

Run/Crank Relay

The run/crank relay control circuit is connected to a constant ground and is switched by the ignition 1 circuit or the body control module (BCM). The BCM, will in lieu of the ignition switch position, activate the Run/Crank relay during a remote start event. The Run/Crank relay supplies a power signal to the following circuits, when the a Run or Crank power mode is selected

1. Automatic transmission shift indicator
2. Automatic transmission (A/T)
3. Switched power feeds to the BCM
4. Electronic brake control module (EBCM)
5. Electronic ignition module (spark control)
6. Electronic power steering module (EPS)
7. Fuel injectors
8. Powertrain control module (PCM)
9. Park neutral position (PNP) switch

Accessory (ACC) Relay

The adaptive cruise control (ACC) relay is energized when the Run or accessory power mode has been selected. The relay uses a Hot At All Times B+ power source derived from the underhood electrical center. The ACC relay is also energized by the body control module (BCM) to supply power during the retained accessory power (RAP) mode. The following devices are controlled by this relay

1. Inside rearview mirror
2. Heated seats
3. Power windows
4. Sunroof
5. Wiper washers switch

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 power mode master (PMM) fail to send a power mode message. The fail-safe plan covers those modules, using exclusively serial data control of power mode, as well as those modules with discrete ignition signal inputs.

Serial Data Messages

The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid power mode master (PMM) message until they can check for the engine run flag status on the serial data circuits. If the PMM 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 power mode master (PMM) 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, battery positive voltage, the modules will fail-safe to the RUN power mode. If the discrete ignition input is not active, open or 0 volts, 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.

BCM Wake-Up/Sleep States

The body control module (BCM) is able to control or perform all of the BCM functions in the wake-up state. The BCM enters the sleep state when active control or monitoring of system functions has stopped, and the BCM has become idle again. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors for these inputs during the sleep state, where the BCM is able to detect switch transitions that cause the BCM to wake-up when activated or deactivated. Multiple switch inputs are needed in order to sense both the insertion of the ignition key and the power mode requested.

The BCM will enter a wake-up state, if any of the following wake-up inputs are detected

1. Activity on the serial data line
2. Detection of a battery disconnect and reconnect condition
3. Headlamps are ON.
4. Ignition is turned ON.
5. Key-in-ignition switch
6. Park lamps are ON.
7. RFA message

The BCM will enter a sleep state when all of the following conditions exist

1. The ignition switch is OFF.
2. No activity exists on the serial data line.
3. No outputs are commanded.
4. No delay timers are actively counting.
5. No wake-up inputs are present.

If all these conditions are met, the BCM will enter a low power or sleep condition. This condition indicates that the BCM, which is the power mode master (PMM) of the vehicle, has sent an OFF or OFF-ASLEEP message to the other systems on the serial data line.

Serial Data Control of Retained Accessory Power (RAP)

The 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

1. The BCM receives an input indicating the opening of any compartment door.
2. The BCM internal timer for the RAP expires after approximately 10 minutes.
3. The BCM detects a decrease in battery capacity below a prescribed limit.
4. The Radio uses an exclusive RAP message that can not be circumvented by any door but the drives door.

The BCM then sends a serial data power mode message ending the RAP function.

The radio is the only module that is controlled by the serial data circuits.

Relay Control of Retained Accessory Power (RAP)

The body control module (BCM) keeps the accessory relay energized during all power modes, except Off-Awake and Crank.

The devices powered by the accessory relay during the retained accessory power (RAP) power mode are the sunroof and windows.

See also:
• Diagnostic System Check - Vehicle
• DTC Symptom Description
• Testing for Intermittent Conditions and Poor Connections
• Power Distribution Schematics
• Master Electrical Component List
• Circuit Testing
• Wiring Repairs
• Connector Repairs
• Diagnostic Trouble Code (DTC) List - Vehicle
• Checking Aftermarket Accessories
• Ignition Switch Replacement
• Radio/Audio System Schematics
• Body Control Module Programming and Setup
• OnStar Schematics
• OnStar Reconfiguration (Gen 5)
• OnStar Reconfiguration (Gen 6.1)
• Digital Radio Receiver Setup
• ABS Schematics
• Service Programming System (SPS)
• Engine Controls Schematics
• Engine Control Module Programming and Setup
• Driver Seat Schematics
• SIR Schematics
• Inflatable Restraint Sensing and Diagnostic Module Programming and Setup
• Instrument Cluster Schematics
• Engine Controls Schematics
• Powertrain Control Module Programming and Setup
• Power Steering System Schematics
• Power Steering Control Module Programming and Setup
• Radio Programming and Setup
• Keyless Entry Schematics
• Transmitter Programming
• Power Sunroof Schematics
• Sunroof Control Module Programming and Setup
• Automatic Transmission Controls Schematics
• Fastener Notice
• Programming Theft Deterrent System Components
• Air Temperature Description and Operation
• Air Delivery Description and Operation
• Interior Lighting Systems Description and Operation
• Indicator/Warning Message Description and Operation
• Power Door Locks Description and Operation
• Cooling System Description and Operation
• Horns System Description and Operation
• Brake Warning System Description and Operation
• Rear Window Defogger Description and Operation
• Seat Belt System Description and Operation
• Wiper/Washer System Description and Operation
• Control Module References
• Body Control Module (BCM) Programming/RPO Configuration
• Body Control Module Replacement
• Scan Tool Does Not Communicate with High Speed GMLAN Device
• Data Link References
• Body Control System Description and Operation
• Retained Accessory Power (RAP) On After Timeout
• Retained Accessory Power (RAP) Inoperative
• Power Mode Description and Operation