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Data Link Communications System: Diagnosis Pontiac Aztek I

Communication Devices 2 illustrations ~1188 words

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 18

Scheme 18: Diagnostic Starting Point - Data Link Communications
Scheme 18: Diagnostic Starting Point - Data Link Communications

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 about five 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 to 16 volts.
  2. Diagnostic trouble codes U1300 and U1301 and 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 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 U1000 or U1255 will clear when all critical operating parameters for the module have been associated with an identification number or at the end of the current ignition cycle.
  2. A history DTC U1000 or U1255 will clear upon completion of 100 ignition cycles without a repeated failure.

Diagnostic Aids

When a malfunction occurs while modules are communicating, a Lost Communication DTC is set as a current DTC. When the 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.

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 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 is set. The XXX is equal to the 3 digit identification number of the module.

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.

  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 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.

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 19

Scheme 19: Circuit Description
Scheme 19: Circuit Description

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-180862-S22306487462005073000000) .
  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-180862-S22306487462005073000000) .

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. 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
  3. U1300
  4. U1301
  5. U1305

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