Data Link Communications System: Diagnosis Pontiac Sunfire I

Diagnostic Starting Point - Data Link Communications

Begin the diagnosis of the data link communications system 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 17

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 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. When a module does not associate an ID number with at least one critical parameter within about 5.5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. When more than one critical parameter does not have an ID number associated with it, the DTC will only be reported once.

The table below list the modules on the Class 2 Serial Data Circuit that will set a U1000 or U1255 and should be actively communicating the previously described messages on the Class 2 Serial Data Circuit.

Scheme 18

Conditions for Running the DTC

The ignition switch run power mode is selected.

The modules voltage supply is within normal operating value, approximately 9-16 volts.

Conditions for Setting the DTC

At least one critical operating parameter has not been associated with a modules assigned ID number within about 5.5 seconds after beginning serial data communication.

Action Taken When the DTC Sets

The SERVICE VEHICLE SOON indicator illuminates.

The module will use default values for the missing parameters.

Conditions for Clearing the DTC

1. A current DTC will clear when all critical operating parameters for the module have been associated with an ID number, or at the end of the current ignition cycle.
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 a open fuse to a module occurs while modules are communicating, a Loss of XXX Communication DTC is set as current. When the modules stop communicating, ignition is turned off, the current Loss of XXX Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the ignition is turned on, 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.

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 three digit identification number, is set.

The control module ID number list below provides a method for determining which module is not communicating. A module with a class 2 serial data circuit 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. The modules that can communicate will set a DTC indicating the module that can not communicate.

Scheme 19

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 table.
2. The DTC which is reported the most times.
3. From the lowest number DTC to the highest number DTC.

The ignition switch run power mode is selected.

The modules voltage supply is within normal operating value, approximately 9-16 volts.

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

1. A current DTC will clear when a Node Alive message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

When multiple Loss of Communication DTCs are set concurrently, the cause is likely to be two opens in the class 2 serial data circuit. Use the Control Module ID Number list in order to determine which modules are not communicating. Use the class 2 serial data circuit schematic in order to determine the location of the opens. Refer to DATA LINK CONNECTOR (DLC) SCHEMATICS .

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 20

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. 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-189104-S04388552292005090700000) .
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-189104-S04388552292005090700000) .

The data link connector (DLC) provides operating power for the scan tool at terminal 16 (battery positive voltage) and at terminal 4 (ground). The DLC provides the class 2 serial data signal at terminal 2 and signal ground at terminal 5. The scan tool will power up with the ignition off. Many modules, however, will not communicate unless the ignition is on.

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.

1. The engine will not start when there is a total malfunction of the Class 2 serial data circuit while the engine is not running.
2. The power mode master must be able to communicate over the Class 2 serial data bus in order for the Tech 2 to communicate with the other modules.
3. The PCM on this vehicle has 3 junctions to the Class 2 serial data bus.