Data Link Communication System: Diagnosis Chevrolet Silverado 2500

Diagnostic Starting Point - Data Link

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.

Scheme 8

Circuit Description

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 or U1255 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 body control module (BCM)
2. The driver information center (DIC)
3. The electronic brake control module (EBCM)
4. The HVAC control module
5. The inflatable restraint sensing and diagnostic module (SDM)
6. The instrument panel cluster (IPC)
7. The memory seat module (MSM) w/A45
8. The powertrain control module (PCM)
9. The rear wheel steering control module w/NYS
10. The transfer case shift control module w/4WD
11. The transmission control module (TCM) w/Allison Transmission
12. The vehicle interface unit (VIU) w/UX2

Conditions for Running the DTC

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

Conditions for Setting the DTC

At least one critical operating parameter has not been associated with an identification number within about 5 seconds after beginning class 2 serial data communication.

Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

Conditions for Cleaning 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

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 with not be learned by the other modules so U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 or U1255 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 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. Once an identification number is learned by a module, it will monitor for that modules Node Alive message. Each module ON the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a Node Alive message every 2 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx is set.

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 identification number for 5 seconds, a DTC U1xxx is set.

Scheme 9

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.

At least one critical operating parameter has not been associated with an identification number within about 5 seconds after beginning class 2 serial data communication.

The modules uses a default value for the missing parameter.

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.

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 message 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 all other class 2 serial communication DTCs is inhibited and a DTC will set.

Scheme 10

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.

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 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»(ref-175673-S35558179732005042600000) .
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-175673-S35558179732005042600000) .

Symptoms - Data Link Communications

Important: The following steps must be completed before using the symptom tables.

1. Perform the applicable diagnostic system check before using the Symptom Tables in order to verify that there are no DTCs set.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Data Link Communications Description & Operation»(ref-175673-S27880492582005042600000) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the vehicle systems. Refer to «CHECKING AFTERMARKET ACCESSORIES»(ref-175672-S27030348872005042500000) .
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. See «Scan Tool Does Not Power Up»(ref-175673-S17178733452005042600000) .
2. See «Scan Tool Does Not Communicate With Class 2 Device»(ref-175673-S35558179732005042600000) .

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 DLC allows communication with the modules for diagnostic purposes. DTCs may be set due to this symptom and during this 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 connect to the DLC for may 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 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 7.0 volts during normal operation. Each module can pull this lower during the transmission. The bus is not a 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 the health (SOH) message every 2 seconds to ensure that the module is operation 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.