Data Link Communication System Chevrolet Impala VIII

SPECIFICATIONS

Fastener Tightening Specifications

SCHEMATIC & ROUTING DIAGRAMS

Note. For wiring schematics, refer to SYSTEM WIRING DIAGRAMS (IMPALA) or SYSTEM WIRING DIAGRAMS (MONTE CARLO) .

Scheme 46

Scheme 47

Scheme 48

Scheme 49

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.

Scheme 50

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 1 critical parameter within about 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.

Conditions for Running the DTC

1. Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
2. Diagnostic trouble codes U1300, U1301 and U1305 do not have a current status.
3. The vehicle power mode (ignition switch position) 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 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 module ignition cycle counter reaches the reset threshold, 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 Lost Communication DTC is set as a current DTC. When the modules stop communicating (ignition is turned OFF) 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 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 is set.

Test Description

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

1. 1) - A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
2. 2) - The module which is not communicating is the likely cause of U1000 or U1255 being set. The following modules communicate on the class 2 serial data circuit: Auxiliary Power Drop Connector BCM DIG EBCM IPC PCM Radio SDM OnStar, if equipped with UE1
3. 5) - The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
4. 6) - The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
5. 7) - The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
6. 11) - The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
7. 13) - If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
8. 14) - The module which set U1000 or U1255 is the likely cause of the malfunction.

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 (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 identification number is learned by a module, it will monitor for that module's "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, where xxx is equal to the 3 digit identification number, 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. The modules that can communicate will set a DTC indicating the module that cannot communicate. When no message is detected from a learned identification number for five seconds, a DTC U1xxx, where xxx is equal to the 3 digit identification number, is set.

Scheme 51

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 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 to 16 volts.
2. Diagnostic trouble codes U1300, U1301 and U1305 do not have a current status.
3. The vehicle power mode, ignition switch position, requires serial data communication to occur.

A message from a learned identification number has not been detected for the past 5 seconds.

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. 1) - A module which loses power during an ignition cycle will cause other modules to set Lost Communication DTCs.
2. 2) - A module which loses ground during an ignition cycle will cause other modules to set Lost Communication DTCs.
3. 3) - The malfunction is due to an open in the class 2 serial data circuit or an open in the module.
4. 7) - The module which was not communicating may have set Lost Communication DTCs for those modules that it was monitoring.
5. 9) - The modules which can communicate indicate the module which cannot communicate. You must clear the DTCs from these modules to avoid future misdiagnosis.

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.

Scheme 52

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 under one of the following conditions: Always high Always low
3. The above conditions are met for approximately 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.
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»(/chevrolet/impala/viii-1999-2006/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/impala/viii-1999-2006/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.

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. Diagnostic trouble codes (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. The BCM must be connected to the class 2 serial data circuit for many other modules to communicate with the scan tool.
2. If the class 2 serial data circuit was shorted to ground, U1300 or U1305 will be set as history DTCs. Refer to «DTC U1300, U1301 Or U1305 (Generic Short DTC)»(/chevrolet/impala/viii-1999-2006/remont/communication-devices/#data-link-communication-system) .
3. If the class 2 serial data circuit was shorted to B+ U1301 or U1305 will be set as history DTCs. Refer to «DTC U1300, U1301 Or U1305 (Generic Short DTC)»(/chevrolet/impala/viii-1999-2006/remont/communication-devices/#data-link-communication-system) .

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

1. 2) - A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The following modules communicate on the class 2 serial data circuit: Auxiliary Power Drop Connector BCM DIC EBCM IPC PCM Radio OnStar, if equipped with UE1 SDM Vehicle Interface Unit (VIU), if equipped
2. 3) - The following DTCs may be retrieved with a history status, but 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 having a current status. This indicates that the malfunction occurred when the ignition was ON.
4. 7) - Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
5. 9) - A poor connection at the DLC terminal of the star connector would cause this condition but will not set a DTC.
6. 10) - An open in the class 2 serial data circuit between the DLC and star connector will prevent the scan tool from communicating with the modules. This condition will not set a DTC.
7. 12) - If communication cannot be established the class 2 serial data circuit may be shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in the BCM. When testing wires for a short, make sure there are no modules connected to the wires being tested.
8. 13) - The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must remain connected to the DLC for the other modules to communicate with the scan tool. This test isolates the PCM class 2 serial data circuit.
9. 31) - If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
10. 32) - The communication malfunction may have prevented diagnosis of the customer complaint.

Scheme 53

1. Remove the screws from the data link connector.
2. Reposition the data link connector from the instrument panel.

Installation Procedure

1. Position the data link connector to the instrument panel.
2. Install the screws to the data link connector. Tighten the data link connector screws to 2 N.m (18 in lbs).

Data Link Connector (DLC)

The DLC is a standardized 16 way connector located below the instrument panel and close to the steering column. Both the connector design and location are dictated by industry wide agreement to follow SAE J 1962 standards.

All DLCs are required to provide a power supply, hot at all times, to Pin 16. This circuit is used to power the scan tool. All DLCs provide a power ground at Pin 4 and a clean signal ground at Pin 5.

The class 2 serial data communications circuit is provided at Pin 2 of the DLC.

Class 2 Serial Data Link

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

1. Auxiliary Power Drop Connector
2. Body Control Module (BCM)
3. Driver Information Center (DIC)
4. Electronic Brake Control Module (EBCM)
5. Instrument Panel Cluster (IPC)
6. Powertrain Control Module (PCM)
7. Radio
8. Remote Playback Device - CD Player (if equipped with UQ3)
9. Inflatable Restraint Sensing and Diagnostic Module (SDM)
10. Vehicle Interface Unit (VIU) (if equipped)

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

See also:
• Scan Tool Does Not Communicate With Class 2 Device