Data Communication System: Diagnosis Chevrolet Silverado Classic 3500

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Diagnostic Starting Point - Data Communications

Begin the system diagnosis with Diagnostic System Check - Vehicle . 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.

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

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.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

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 B1000

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

The module microprocessor must be active/awake.

This DTC indicates the keep alive memory (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

As part of normal data processing, the module performs a data programming check on its writes to the electrically erasable read only memory (EEPROM). The EEPROM write error detection is handled inside the control module. No external circuits are involved.

This diagnostic procedure supports the following DTC

DTC B1007 EEPROM Write Error

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

The module writes information to a data block in the EEPROM. The module then reads the data and compares it to what was sent to the data block. If the data does not match after 3 consecutive attempts, the module sets the DTC.

The module writes to another area of the EEPROM, this becomes the new permanent area to store the data. The data location is allowed to change until all of the available EEPROM is used. If a DTC B1004 is also set, the module reverts to base operation values programmed for those blocks of data that have failed. The blocks of data that have not failed the checksum 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 B1007

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

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

Modules connected to the GMLAN serial data circuits 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 .

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 (Diesel)»(ref-277861-S11983862452008012100000) or «Scan Tool Does Not Communicate with High Speed GMLAN Device (HP2)»(ref-277861-S23159307672008012100000) .
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 (Diesel)»(ref-277861-S11983862452008012100000) or «Scan Tool Does Not Communicate with High Speed GMLAN Device (HP2)»(ref-277861-S23159307672008012100000) .

Modules connected to the controller area network (CAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. If no communication is detected on CAN serial data circuit, the DTC is set. A total non communication condition may be caused by a short to battery or voltage on any of the CAN circuits or a short between the CAN high and low circuits.

The following modules communicate on CAN serial data (LLY engine)

1. The engine control module (ECM)
2. The transmission control module (TCM)
3. The fuel injector control module (FICM)
4. The glow plug controller module (GPCM)

This diagnostic procedure supports the following DTC

DTC U0073 High Speed CAN Communication Bus

Conditions for Running the DTCs

1. Voltage supplied to the modules is in the normal operating voltage range.
2. The engine is running.

A total non communication condition is detected on CAN serial data circuit.

1. The module uses a default value for the missing parameter.
2. The malfunction indicator lamp (MIL) will illuminate on the second consecutive ignition cycle that the diagnostic runs and fails, for the type B DTCs. For a detailed description about DTC types, refer to «Powertrain Diagnostic Trouble Code (DTC) Type Definitions»(ref-277883-S33988416012008012100000) .

Conditions for Clearing the MIL/DTC

The MIL/DTC clearing depends on DTC type. For information about DTC types, refer to Diagnostic Trouble Code (DTC) Types .

DTC Type B

1. The MIL clears after 3 ignition cycles when the malfunction is no longer present.
2. A current DTC clears when the malfunction is no longer present.
3. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DTC Type C

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 U0073

Modules connected to the high speed 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 prerecorded information about what messages are needed to be exchanged on the serial data circuits. 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. A module with a high speed GMLAN serial data circuits 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. If any of the high speed GMLAN circuits are shorted to battery voltage, ground or between them, no communication is possible on high speed GMLAN serial data bus, and a DTC U0073 is set.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC U0100 Lost Communication With Engine Control Module (ECM)
2. DTC U0101 Lost Communication With Transmission Control Module (TCM)
3. DTC U0106 Lost Communication With Glow Plug Control Module (GPCM)

1. Voltage supplied to the modules is in the normal operating voltage range.
2. The engine is running.

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

1. The module uses a default value for the missing parameter.
2. The malfunction indicator lamp (MIL) will illuminate on the second consecutive ignition cycle that the diagnostic runs and fails, for the type B DTCs. For a detailed description about DTC types, refer to «Powertrain Diagnostic Trouble Code (DTC) Type Definitions»(ref-277883-S33988416012008012100000) for the 6.6L (LLY) engine.

The MIL/DTC clearing depends on DTC type. For information about DTC types, refer to Diagnostic Trouble Code (DTC) Types for the 6.6L (LLY) engine.

1. DTC type B The MIL clears after 3 ignition cycles when the malfunction is no longer present. A current DTC clears when the malfunction is no longer present. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
2. DTC type C A current DTC clears when the malfunction is no longer present. 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.

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. There are two 120 ohm resistors between the GMLAN serial data (+) and (-) circuits. One is internal to the powertrain control module (PCM) and the other is internal to the energy storage control module (ESCM). When tested between the GMLAN serial data (+) and (-) circuits at the DLC with the ignition key OFF, normal resistance is 55-65 ohms.

Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits. 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. When a message that indicates the availability of the transmitter module is not received, the receiver module sets a DTC.

This diagnostic procedure supports the following DTCs

1. DTC U0111 Lost Communication With Energy Storage Control Module (ESCM)
2. DTC U0120 Lost Communication With Starter/Generator Control Module (SGCM)
3. DTC U0131 Lost Communication With Electro-Hydraulic Power Steering (EHPS) Module
4. DTC U0293 Lost Communication With Hybrid Control Module (HCM)

Voltage supplied to the modules is in the normal operating voltage range.

A supervised periodic message that includes the transmitter module availability has not been received by powertrain control module (PCM) from one or more of the high speed GMLAN modules.

1. The MIL may illuminate.
2. The Hybrid Engine Idle Off feature may not operate properly.

1. The MIL clears after 3 ignition cycles when the malfunction is no longer present.
2. A current DTC clears when the malfunction is no longer present.
3. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

The following conditions may cause the DTC to set

1. A poor connection or terminal tension at a GMLAN module
2. An intermittent open on either high speed GMLAN serial data circuit
3. An open voltage or ground circuit to a module
4. An internal module malfunction
5. A short between the GMLAN serial data circuits
6. A short to voltage or ground on either of the GMLAN serial data circuits

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within 5 seconds of beginning serial data communication, DTC U1000 is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once.

The class 2 serial data line on this vehicle is a star configuration. The following modules communicate on the class 2 serial data line

1. The audio amplifier (AMP), w/UQ7 and Y91
2. The body control module (BCM)
3. The communication interface module (OnStar®), w/UE1
4. The digital radio receiver (DRR), w/U2K
5. The driver door module (DDM)
6. The electronic brake control module (EBCM)
7. The generator battery control module (GBCM)
8. The HVAC control module
9. The hybrid control module (HCM), w/HP2
10. The inflatable restraint sensing and diagnostic module (SDM)
11. The instrument panel cluster (IPC)
12. The memory seat module (MSM), w/AN3
13. The passenger door module (PDM)
14. The powertrain/engine control module (PCM/ECM)
15. The radio
16. The rear seat audio (RSA) controller, w/UK6
17. The rear seat entertainment (RSE) assembly w/U42
18. The rear wheel steering control module (RWSCM), w/NYS
19. The remote playback device - CD player (CDX), w/U1S
20. The transfer case shift control module (TCSCM), w/NP1/NP8
21. The transmission control module (TCM), w/M74

This diagnostic procedure supports the following DTC

DTC U1000 Class 2 Data Link Malfunction

1. Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
2. DTCs U1300, U1301 or U1305 do not have a current status.
3. The vehicle power mode requires serial data communication to occur.

A node alive message has not been received from an unidentified module within the last 5 seconds after establishing class 2 serial data communication.

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.

When a malfunction occurs while modules are communicating, a lost communication DTC is set as a current DTC. When the modules stop communicating the current lost communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so U1000 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 is set.

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification (ID) number of the module which sent the message for state of health monitoring/node alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an ID number is learned by a module, it will monitor for that modules node alive message. Each module on the class 2 serial data circuit is required to send a Node Alive message every 2 seconds. When no message is detected from a learned ID number for 5 seconds, a DTC U1XXX. XXX is equal to the 3 digit ID number of the module.

The control module ID number list provides a method for determining which module is not communicating. A module with an internal class 2 serial data circuit malfunction or which loses power during the current ignition cycle would have a lost communication DTC set by other modules. Use the control module ID number list in order to determine which module is not communicating and the lost communications with XXX diagnostic table in order to diagnose the malfunction. When no message is detected from a learned ID number for 5 seconds, a DTC U1XXX is set.

The Control Module ID

When more than one loss of communication DTC is set in a single module or among multiple modules, diagnose the DTCs in the following order

1. Current DTCs before history DTCs except as specified in the diagnostic tables
2. The DTC which is reported the most times.
3. From the lowest number DTC to the highest number DTC

1. Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
2. DTCs U1300, U1301 or U1305 do not have a current status.
3. The vehicle power mode requires serial data communication to occur.

A node alive message has not been received from an identified module within the last 5 seconds.

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. An intermittent open between a module and a star connector may cause this DTC to set.
2. A poor connection at a module or a star connector may cause this DTC to set.
3. An intermittent open in a star connector may cause this DTC to set.
4. An open voltage or ground circuit to a module may cause this DTC to set.
5. An internal module malfunction may cause this DTC to set.

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. In addition to this, Node Alive messages are transmitted by each module on the class 2 serial data circuit about once every 2 seconds. When the module 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.

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

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

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. These DTCs cannot be retrieved with a current status. Diagnosis of current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with a Class 2 Device. Refer to «Scan Tool Does Not Communicate with Class 2 Device»(ref-277861-S27350415002008012100000) .
2. An intermittent condition is likely to be caused by a short on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate with a Class 2 Device procedure in order to isolate an intermittent condition. Refer to «Scan Tool Does Not Communicate with Class 2 Device»(ref-277861-S27350415002008012100000) .

Modules connected to the class 2 and high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. All DTCs in this range are reported on class 2 link to the scan tool by powertrain control module (PCM) even if they may be set by different modules.

This diagnostic procedure supports the following DTCs

1. DTC U1881 Electro-Hydraulic Power Steering (EHPS) Module Lost Communication With Energy Storage Control Module (ESCM)
2. DTC U1882 Energy Storage Control Module (ESCM) Lost Communication With Electro-Hydraulic Power Steering (EHPS) Module
3. DTC U1883 Hybrid Control Module (HCM) Lost Communication With Driver Door Module (DDM)
4. DTC U1884 Hybrid Control Module (HCM) Lost Communication With Passenger Door Module (PDM)
5. DTC U1885 Energy Storage Control Module (ESCM) Lost Communication With Hybrid Control Module (HCM)
6. DTC U1886 Energy Storage Control Module (ESCM) Lost Communication With Powertrain Control Module (PCM)
7. DTC U1887 Energy Storage Control Module (ESCM) Lost Communication With Starter/Generator Control Module (SGCM)
8. DTC U1888 Hybrid Control Module (HCM) Lost Communication With Energy Storage Control Module (ESCM)
9. DTC U1889 Hybrid Control Module (HCM) Lost Communication With Body Control Module (BCM)
10. DTC U1890 Hybrid Control Module (HCM) Lost Communication With HVAC Control Module
11. DTC U1891 Hybrid Control Module (HCM) Lost Communication With Instrument Panel Cluster (IPC)
12. DTC U1892 Hybrid Control Module (HCM) Lost Communication With Electro-Hydraulic Power Steering (EHPS) Module
13. DTC U1893 Hybrid Control Module (HCM) Lost Communication With Powertrain Control Module (PCM)
14. DTC U1894 Hybrid Control Module (HCM) Lost Communication With Starter/Generator Control Module (SGCM)
15. DTC U1895 Electro-Hydraulic Power Steering (EHPS) Module Lost Communication With Powertrain Control Module (PCM)
16. DTC U1896 Electro-Hydraulic Power Steering (EHPS) Module Lost Communication With Starter/Generator Control Module (SGCM)
17. DTC U1897 Starter/Generator Control Module (SGCM) Lost Communication With Energy Storage Control Module (ESCM)
18. DTC U1898 Starter/Generator Control Module (SGCM) Lost Communication With Hybrid Control Module (HCM)
19. DTC U1899 Starter/Generator Control Module (SGCM) Lost Communication With Powertrain Control Module (PCM)

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

A node alive message has not been received from an identified module within the last 5 seconds after establishing class 2 serial data communication or a supervised high speed GMLAN message 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. An intermittent open between a module and a star connector may cause this DTC to set.
2. An intermittent open on high speed GMLAN may cause this DTC to set.
3. An open voltage or ground circuit to a module may cause this DTC to set.
4. An internal module malfunction may cause this DTC to set.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the systems. Refer to «Checking Aftermarket Accessories»(ref-277884-S30236091172008012100000) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

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»(ref-277861-S12755652362008012100000)
2. «Scan Tool Does Not Communicate with Class 2 Device»(ref-277861-S27350415002008012100000)
3. «Scan Tool Does Not Communicate with High Speed GMLAN Device (Diesel)»(ref-277861-S11983862452008012100000) or «Scan Tool Does Not Communicate with High Speed GMLAN Device (HP2)»(ref-277861-S23159307672008012100000)

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.

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes.

The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication

1. A class 2 serial data circuit shorted to ground.
2. A class 2 serial data circuit shorted to voltage.
3. An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit.

Diagnostic Fault Information

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

Scan Tool Does Not Communicate with High Speed GMLAN Device (Diesel)

1. Use the «Data Link References»(ref-277861-S09528650302008012100000) to identify the high speed GMLAN serial data modules.
2. This test is used for a total high speed GMLAN communication failure. If only 1 module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use «DTC U0100-U0299 (Diesel Engine)»(ref-277861-S41689585982008012100000) or «DTC U0100-U0299 (HP2)»(ref-277861-S39379043732008012100000) for diagnostics.
3. Use the DMM MIN/MAX function to capture/locate intermittent conditions.
4. The following conditions may cause a total loss of high speed GMLAN data communication: A short between high speed GMLAN (+) and high speed GMLAN (-) circuits Any of the high speed GMLAN serial data circuits shorted to ground or voltage A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits An open in a high speed GMLAN serial data circuit between the DLC and the first splice. This open will cause no communication with the scan tool, and will not effect the module communication on the vehicle.

Circuit/System Testing

Automatic Transmission

1. Ignition OFF, disconnect the harness connector of the GPCM.
2. Ignition ON, with a scan tool attempt to communicate with the ECM/PCM. Communication should not be available. If the ECM/PCM communicates, replace the GPCM.
3. Disconnect the ECM/PCM. Ignition ON, with a scan tool attempt to communicate with the TCM. Communication should not be available. If the TCM communicates, replace the ECM/PCM.
4. All 3 modules disconnected, test for less than 5 ohms of resistance between the DLC and the TCM on both high speed GMLAN serial data circuits. If greater than 5 ohms, repair the data circuit for open/high resistance between the DLC and the first splice.
5. All 3 modules disconnected, test for infinite resistance between all 4 of the high speed GMLAN serial data (+) and (-) circuits of the TCM. If less than infinite resistance, repair the short between the serial data circuits.
6. Ignition on and all 3 modules disconnected, test for less than 1.0 volt between the high speed GMLAN serial data circuits of the TCM and ground. If greater than 1.0 volt, repair the serial data circuit of the TCM for a short to voltage.
7. All 3 modules disconnected, test for infinite resistance between the high speed GMLAN serial data circuits of the TCM and ground. If less than infinite resistance, repair the serial data circuits for a short to ground.
8. If all circuits test normal, replace the TCM.

Manual Transmission

1. Ignition OFF, disconnect the harness connector of the GPCM.
2. Ignition ON, with a scan tool attempt to communicate with the ECM/PCM. Communication should not be available. If the ECM/PCM communicates, replace the GPCM.
3. Test for less than 5 Ohms of resistance between the DLC and the ECM/PCM on both high speed GMLAN serial data circuits. If greater than 5 Ohms, repair the data circuit for open/high resistance between the DLC and the first splice.
4. Both modules disconnected, test for infinite resistance between the high speed GMLAN serial data (+) and (-) circuits of the DLC. If less than infinite resistance, repair the short between the serial data circuits.
5. Ignition on and both modules disconnected, test for less than 1.0 volt between the high speed GMLAN serial data circuits of the DLC and ground. If greater than 1.0 volt, repair the serial data circuit for a short to voltage.
6. Both modules disconnected, test for infinite resistance between the high speed GMLAN serial data circuits of the DLC and ground. If less than infinite resistance, repair the serial data circuits for a short to ground.
7. If all circuits test normal, replace the ECM/PCM.

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.

The scan tool communicates with the following modules via the high speed GMLAN

1. Energy Storage Control Module (ESCM)
2. Starter/Generator Control Module (SGCM)
3. Electro-Hydraulic Power Steering (EHPS) Module

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

Scan Tool Does Not Communicate with High Speed GMLAN Device (HP2)

The serial data communication among the control modules is performed through multiple serial data communication links. The class 2 serial data line is always present. The high speed GMLAN or controller area network (CAN) may be present for different vehicle options. The data link connector (DLC) allows a scan tool to communicate with the modules on class 2 or high speed GMLAN serial data lines. In order for the scan tool to communicate with the modules on high speed GMLAN link, a CANdi module is needed. The CANdi module behaves as an interface between the scan tool and the high speed GMLAN data link. The CAN is used for functional communication only, among the modules connected to it.