Test Description

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

1. 3:  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 engine control module (ECM) and the transmission control module (TCM) communicate functionally on both high speed GMLAN and class 2 serial data circuits. The ECM and TCM communicate with the scan tool on high speed GMLAN only. The auxiliary gage center, w/ERG or ERH, is on class 2 serial data bus but doesn't have diagnostic capability. The following modules communicate with the scan tool on the class 2 serial data circuit:
   • The audio amplifier (AMP), w/Bose
   • The body control module (BCM)
   • The electronic brake control module (EBCM)
   • The inflatable restraint sensing and diagnostic module (SDM)
   • The instrument panel cluster (IPC)
   • The memory seat module (MSM) - driver, w/AAB
   • The radio
   • The remote control door lock receiver (RCDLR)
   • The roof/door module (RDM)
2. 4:  The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
   • U1300
   • U1301
   • U1305
3. 7:  A state of health DTC with a history status may be present along with a U1000 or U1255 code having a current status. This indicates that the malfunction occurred when the ignition was ON.
4. 8:  Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
5. 11:  A poor connection at the DLC terminal of the splice pack SP201 would cause this condition but will not set a DTC.
6. 12:  An open or a short in the class 2 serial data circuit between the DLC and splice pack SP201 will prevent the scan tool from communicating with any module. This condition will not set a DTC.