Test Description

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

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.
The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
- U1300
- U1301
- U1305
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.
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.
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.
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.
If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
The communication concern may have prevented diagnosis of the customer complaint.

Fig 1: Scan Tool Does Not Communicate With Class 2 Device Diagnostic Procedure (Steps 1-4)
Courtesy of GENERAL MOTORS CORP.

Fig 2: Scan Tool Does Not Communicate With Class 2 Device Diagnostic Procedure (Steps 5-10)
Courtesy of GENERAL MOTORS CORP.

Fig 3: Scan Tool Does Not Communicate With Class 2 Device Diagnostic Procedure (Steps 11-15)
Courtesy of GENERAL MOTORS CORP.

Fig 4: Scan Tool Does Not Communicate With Class 2 Device Diagnostic Procedure (Steps 16-22)
Courtesy of GENERAL MOTORS CORP.