Data Link Communication System Chevrolet Chevy Express G2500

Data Link Communications Schematic Icons

Data Link Communications 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

Data Link Connector (DLC) Schematics

For data link connector schematics refer to appropriate SYSTEM WIRING DIAGRAMS article.

Scheme 1

Scheme 2

Data Link Communications Connector End Views

Data Link Connector (DLC) Connector End Connector Part Information 12110250 16-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function 1 - - Not Used 2 PU 1132 Class 2 Serial Data 3 - - Not Used 4 BK/WH 351 Ground 5 BK/WH 351 Ground 6-15 - - Not Used 16 RD/WH 640 Battery Positive Voltage

SP200 Connector End Connector Part Information 12176461 12-Way F GT 150 Splice Saver (BK) Pin Wire Color Circuit No. Function A PU 1132 Class 2 Serial Data B D-GN 1049 Class 2 Serial Data C - - Not Used D GY 1036 Class 2 Serial Data E L-BU 1122 Class 2 Serial Data F D-BU 1128 Class 2 Serial Data G OG 1044 Class 2 Serial Data H YE 1127 Class 2 Serial Data (UE1) J PK 1045 Class 2 Serial Data (AU0) K-L - - Not Used M L-GN 1037 Class 2 Serial Data

Diagnostic Starting Point - Data Link Communications

Begin the diagnosis of the data link communications by performing the Diagnostic System Check for the system in which the customer concern is apparent. The Diagnostic System Check will direct you to the correct procedure within the Data Link Communications section when a communication malfunction is present.

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

Each module connected to the class 2 serial data circuit monitors serial data communication during normal vehicle operation. Operating parameters and other information are exchanged among the modules. When a module receives a message that contains a critical operating parameter, the module records the identification number of the module which sent the message. If a module does not associate an identification number with every critical parameter within 5 seconds of beginning serial data communication, DTC U1000 or U1255 will set.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC U1000 Class 2 Data Link
2. DTC U1255 Class 2 Data Link

Conditions for Running the DTC

1. Battery Voltage is 9-16 volts.
2. DTCs U1300, U1301, or U1305 are not current.
3. The vehicle power mode requires serial data communication to occur.

Conditions for Setting the DTC

A message containing a critical operating parameter has not been received within 5 seconds after establishing class 2 serial data communication.

Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

Conditions for Clearing the DTC

1. A current DTC clears when the ignition is cycled, and the malfunction is no longer present.
2. A history DTC clears when the ignition has been cycled 100 times, without a repeat of the malfunction.

Diagnostic Aids

When a malfunction such as an open fuse to a module occurs while modules are communicating, a DTC U1001-1254 Lost Communications with XXX is set current. When the ignition is turned OFF, the current DTC U1001-1254 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 DTC U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only DTC U1000 or U1255 will set.

Test Description

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

1. 1: A DTC U1001 - U1254 Lost Communications with XXX with a history status may indicate the cause of U1000 or U1255.
2. 2: The modules not communicating are the likely cause of DTC U1000 or U1255. The modules that are available on the class 2 serial data circuit are listed in the Circuit Description.
3. 6: The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set DTC U1001 - U1254 Lost Communications with XXX for those modules that it was monitoring.
4. 9: The modules which can communicate indicate the module which cannot communicate. You must clear the serial data communication DTCs from these modules to avoid future misdiagnosis.
5. 12: If all modules are communicating, the module which set DTC U1000 or U1255 may have done so due to some other condition.
6. 14: The module which set U1000 or U1255 is the likely cause of the malfunction.

DTC U1000 & U1255

Each module connected to the class 2 serial data circuit monitors serial data communication 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. Once a module learns another modules identification number, it will monitor the serial data for that modules node alive message. Each module that sends critical operating parameters is required to send a node alive message every two seconds. If no message is detected from a learned module for five seconds, DTC U1001-U1254 will set.

This diagnostic procedure supports the following DTCs

1. DTC U1016 Lost Communications With Powertrain Control Module (PCM)
2. DTC U1041 Lost Communications With Electronic Brake Control Module (EBCM)
3. DTC U1064 Lost Communications With Body Control Module (BCM)
4. DTC U1088 Lost Communications With Sensing and Diagnostic Module (SDM)
5. DTC U1096 Lost Communications With Instrument Panel Cluster (IPC)
6. DTC U1128 Lost Communications With Radio
7. DTC U1151 Lost Communications With Onstar (VCIM)
8. DTC U1176 Lost Communications With Remote Function Actuation (RCDLR)

1. Battery Voltage is 9-16 volts.
2. DTCs U1300, U1301 or U1305 are not current.
3. The vehicle power mode requires serial data communication to occur.

A node alive message has not been received from a 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 ignition is cycled, and the malfunction is no longer present.
2. A history DTC clears when the ignition has been cycled 100 times, 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.

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

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

1. 6: The module which was not communicating on the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.

DTC U1001-U1254

Each control module connected to the class 2 serial data circuit monitors the voltage on the circuit. If a control module detects the class 2 serial data circuit is open or shorted for 3 seconds, all other class 2 serial communication DTCs are inhibited and DTC U1300, U1301, or U1305 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

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 always low or always high.
3. The above conditions are met for 3 seconds.

Action Taken When the DTCs Sets

1. The module inhibits the setting of all other class 2 DTCs.
2. 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, or when the ignition is cycled.
2. A history DTC clears when the ignition has been cycled 100 times, without a repeat of the malfunction.

1. DTCs U1300, U1301, and U1305 cannot be retrieved while the condition is present. Diagnosis of these DTCs 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»(/chevrolet/chevy-express-g2500/1996-2012/remont/communication-devices/#data-link-communication-system) .
2. An intermittent condition is likely to be caused by a short or an open 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»(/chevrolet/chevy-express-g2500/1996-2012/remont/communication-devices/#data-link-communication-system) .

Symptoms - Data Link Communications

1. Perform the Diagnostic System Check for the subsystem exhibiting the symptoms. The subsystem diagnostic system check will identify where to begin diagnosis of the data link communication system.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Data Link Communications Description and Operation»(/chevrolet/chevy-express-g2500/1996-2012/remont/communication-devices/#data-link-communication-system) .

Visual/Physical Inspection

1. Inspect for aftermarket devices that could affect the operation of the serial data communications systems. Refer to «Checking Aftermarket Accessories»(/chevrolet/chevy-express-g2500/1996-2012/remont/body-electrical/#wiring-systems-diagnostic-information-and-procedures__checking-aftermarket-accessories) in Wiring Systems.
2. Inspect the easily accessible systems or visible system components for obvious damage or conditions that 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/chevy-express-g2500/1996-2012/remont/communication-devices/#data-link-communication-system)
2. «Scan Tool Does Not Communicate with Class 2 Device»(/chevrolet/chevy-express-g2500/1996-2012/remont/communication-devices/#data-link-communication-system)

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

Each module connected to the class 2 serial data circuit monitors serial data communication during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules 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.

1. The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must be connected to the DLC for any other module to communicate with the scan tool.
2. When the class 2 serial data circuit: is shorted to ground is shorted to voltage

The following DTCs may set

1. U1300
2. U1301
3. U1305

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

1. 2: A partial 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. 4: The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition. U1300 U1301 U1305
3. 6: A State of Health DTC with a history status may be present along with a U1000 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.
4. 10: Normal class 2 serial data communication cannot take place until the Body Control Module (BCM) sends the appropriate power mode message. If the BCM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate. Early 2004 model vehicles have a redundant class 2 serial data circuit between the BCM and PCM. Late 2004 model vehicles do not have this circuit and it is not necessary to disconnect the PCM to perform this step.
5. 12: Normal class 2 serial data communication cannot take place until the Body Control Module (BCM) sends the appropriate power mode message. If the BCM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
6. 17: If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
7. 18: The communication concern may have prevented diagnosis of the customer complaint.

Scan Tool Does Not Communicate With Class 2 Device

The Data Link Connector (DLC) allows a scan tool to communicate with the class 2 serial data line. The serial data line is the means by which the microprocessor-controlled modules in the vehicle communicate with each other. Once the scan tool is connected to the class 2 serial data line through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for Diagnostic Trouble Codes (DTCs). Class 2 serial data is transmitted on a single wire at an average of 10.4 kbps. This value is an average; class 2 uses a variable pulse width modulation to carry data and depending on the message it may operate faster or slower. The bus will float at a nominal 7 volts during normal operation. Each module can pull this lower during the transmission.

The bus is not at battery positive voltage or ground potential during normal operation. When the ignition switch is in RUN, each module communicating on the class 2 serial data line sends a State Of Health (SOH) message every 2 seconds to ensure that the module is operating properly. When a module stops communicating on the class 2 serial data line, for example, if the module loses power or ground, the SOH message it normally sends on the data line every 2 seconds disappears. Other modules on the class 2 serial data line, which expect to receive that SOH message, detect its absence; those modules in turn set an internal DTC associated with the loss of SOH of the non-communicating module. The DTC is unique to the module which is not communicating; for example, when the inflatable restraint Sensing and Diagnostic Module (SDM) SOH message disappears, several modules set DTC U1088. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.

On some vehicles, if the Powertrain Control Module (PCM) is unable to communicate with the Vehicle Theft Deterrent (VTD) system after the vehicle has started, the PCM will consider the VTD system to be malfunctioning. The PCM will enter a fail enable state and will command the security indicator to illuminate. When the PCM is in a fail enable state, the vehicle will NOT stall or stop running. If the PCM is in a fail enable state when the ignition is switched OFF, the PCM will remain fail enable until communications with the VTD system has been restored. When the PCM is in a fail enable state, the VTD system is NOT active and the vehicle will start. This feature is NOT available on all GM vehicle lines.

Class 2 Serial Data Link

The class 2 serial data link allows the following modules to communicate with each other

1. The Body Control Module (BCM)
2. The Electronic Brake Control Module (EBCM)
3. The inflatable restraint Sensing and Diagnostic Module (SDM)
4. The Instrument Panel Cluster (IPC)
5. The Powertrain Control Module (PCM)
6. The radio
7. The Remote Control Door Lock Receiver (RCDLR)
8. The Vehicle Communication Interface Module (VCIM)

The class 2 serial data link also allows a scan tool to communicate with the above modules for diagnostic and testing purposes.

The class 2 serial data link on early 2004 vehicles is a ring/star configuration. The class 2 serial data link on late 2004 vehicles is a star configuration. The class 2 serial data circuits are bussed together via the DLC connector and SP200. Refer to Data Link Communications Component Views for the location of the DLC and SP200.

Data Link Connector (DLC)

The Data Link Connector (DLC) allows a scan tool to communicate with the class 2 modules. The DLC is a standardized 16 cavity connector located below the instrument panel and close to the steering column. Connector design and location is dictated by an industry wide standard, and it 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. Class 2 serial data signal at terminal 2.
4. Common signal ground at terminal 5.

Refer to Data Link Communications Connector End Views .

Diagnostic Trouble Codes (DTCs)

Each control module connected to the class 2 serial data circuit monitors serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. In addition, node alive messages are transmitted by each module on the class 2 serial data circuit about once every 2 seconds. If a module does not receive a node alive message when expected, a DTC will set. If a module detects that the class 2 serial data circuit is shorted, the setting of all other class 2 serial communication DTCs is inhibited, and DTC U1300, U1301, or U1305 will set.

See also:
• Master Electrical Component List
• Inline Harness Connector End Views
• Control Module References
• Circuit Testing
• Wiring Repairs
• Testing for Intermittent Conditions and Poor Connections
• Connector Repairs
• Checking Aftermarket Accessories
• DTC U1000 and U1255
• Data Link Connector (DLC) Schematics
• Data Link Communications Connector End Views