Test Description

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.
Fig 1: Scan Tool Does Not Communicate With Class 2 Device (1 Of 5)
Courtesy of GENERAL MOTORS CORP.
Fig 2: Scan Tool Does Not Communicate With Class 2 Device (2 Of 5)
Courtesy of GENERAL MOTORS CORP.
Fig 3: Scan Tool Does Not Communicate With Class 2 Device (3 Of 5)
Courtesy of GENERAL MOTORS CORP.
Fig 4: Scan Tool Does Not Communicate With Class 2 Device (4 Of 5)
Courtesy of GENERAL MOTORS CORP.
Fig 5: Scan Tool Does Not Communicate With Class 2 Device (5 Of 5)
Courtesy of GENERAL MOTORS CORP.