Data Link Communication System: Diagnosis Chevrolet SSR I

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 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 Loss of XXX Communications is set current. When the modules stop communicating the current DTC U1001-1254 Loss of XXX Communications 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 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.

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 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. When no message is detected from a learned module for 5 seconds, DTC U1001-U1254 will set.

This diagnostic procedure supports the following DTCs

1. DTC C0292 Lost Communications With Engine Control System (PCM)
2. DTC U1016 Lost Communications With Powertrain Control Module (PCM)
3. DTC U1041 Lost Communications With Electronic Brake Control Module (EBCM)
4. DTC U1064 Lost Communications With Body Control Module (BCM)
5. DTC U1088 Lost Communications With Sensing and Diagnostic Module (SDM)
6. DTC U1096 Lost Communications With Instrument Panel Cluster (IPC)
7. DTC U1128 Lost Communications With Radio
8. DTC U1176 Lost Communications With Remote Function Actuation (RCDLR)
9. DTC U1177 Lost Communications With Folding Top Controller (RDM)

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 with a learned identification number 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 ignition has been cycled 100 times, without a repeat of the malfunction.

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

Any of the following conditions may cause DTC U1001-U1254 to set

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

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.

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»(ref-187791-S27922850272005090100000) .
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»(ref-187791-S27922850272005090100000) .

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»(ref-187791-S12935131892005090100000) .

Visual/Physical Inspection

1. Inspect for aftermarket devices that could affect the operation of the serial data communications systems. Refer to «Checking Aftermarket Accessories»(ref-187796-S08905438042005090100000) in Wiring Systems.
2. Inspect the easily accessible systems or visible system components for obvious damage or conditions that 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-187791-S27446017452005090100000)
2. «Scan Tool Does Not Communicate with Class 2 Device»(ref-187791-S27922850272005090100000)

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.

Each 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. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes.

1. 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.
2. The body control module (BCM) must be connected to the class 2 serial data circuit for any other module to communicate with the scan tool. The BCM detects that the ignition is ON and sends the appropriate power mode message to wake up the other modules.
3. When the class 2 serial data circuit is shorted to ground or voltage, the following DTCs may set: U1300 U1301 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 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.

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.