Data Link Communications System: Overview Pontiac Aztek I

Test Description

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

Scheme 6

Scheme 7

1. A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
2. The modules which are not communicating are the likely cause of U1000 or U1255 being set. The following modules communicate on the class 2 serial data circuit: BCM EBCM HUD HVAC Control Module (CJ2) IPC MSM (A43) PCM Radio SDM Theft Deterrent Control Module VIU (UG1) Devices on the Auxiliary Power Drop Connector
3. The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
4. The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
5. The modules which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
6. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
7. If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
8. The module which set U1000 or U1255 is the likely cause of the malfunction.

Scheme 8

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.

The number below refers to the step number on the diagnostic table.

Scheme 9

Scheme 10

1. 6. The module which was not communicating on the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.

The number below refers to the step number on the diagnostic table.

1. If the battery positive voltage and ground circuits of the DLC are functioning properly. The malfunction must be due to the scan tool.

Scheme 11

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

Scheme 12

Scheme 13

Scheme 14

Scheme 15

1. 2. A partial loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.
2. The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition. U1300 U1301 U1305
3. A State of Health DTC with a history status may be present along with a U1000 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.
4. Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
5. Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
6. Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
7. If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
8. The communication concern may have prevented diagnosis of the customer complaint.

Scheme 16

1. Remove the bolts/screws from the data link connector.
2. Remove the lower data link connector.

Scheme 17

1. Place the data link connector into position.
2. Install the bolts/screws to the data link connector. Tighten Tighten the bolts/screws to 2 N.m (18 lb in).

Data Link Communications Description and Operation

The serial data line is the means by which the microprocessor-controlled modules in the vehicle communicate with each other. Each module is assigned a specific recognition code known as source ID. This code is used to identify which module is communicating on the serial data circuit. When a message is sent out on the serial data circuit, the recognition code will identify which particular module sent the message. These messages contain specific information, or commands, modules require to function properly. When a module receives a message it also "learns" the source ID of the module that sent it. This source ID is used to determine which module actually sent the message and for state of health (SOH) monitoring. When the ignition switch is in RUN, each module communicating on the class 2 serial data line sends a 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 expecting the source ID then 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 body control module (BCM) SOH message disappears, several modules set DTC U1064. Note that a loss of serial data DTC does not normally represent a failure of the module that set it. Description and diagnosis of each module controlled system will be covered in the respective service manual section.