Scan Tool Does Not Communicate With Class 2 Device

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. 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.

DIAGNOSTIC AIDS
^ 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.
^ When the class 2 serial data circuit:
^ is shorted to ground
^ is shorted to voltage

The following DTCs may set:
^ U1300
^ U1301
^ U1305

TEST DESCRIPTION

Steps 1-9:

Steps 10-13:

Steps 14-18:

Steps 19-25:

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.
4. The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
^ U1300
^ U1301
^ U1305
6. 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.
10. 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.
12. Disconnecting the splice pack(s) and/or class 2 circuits one at a time and attempting to communicate with any module still connected to the class 2 serial data circuit, will determine whether or not the concern is in the splice pack portion of the class 2 serial data circuit.
13. Connecting the class 2 serial data circuits to the suspect splice pack one at a time while attempting to communicate with any module still connected to the class 2 serial data circuit, will determine which circuit or module on the splice pack is causing the concern.
14. Splitting the class 2 serial data circuit will help isolate the location of the malfunction. If communication can be established, the concern is located in the wiring or one of the modules that is no longer connected to the DLC. If communication cannot be established, the concern is located in the wiring or one of the modules that is still connected to the DLC.
22. If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
23. The communication concern may have prevented diagnosis of the customer complaint.