Scan Tool Does Not Communicate With Class 2 Device

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.

DIAGNOSTIC AIDS
The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication:
- A class 2 serial data circuit shorted to ground.
- A class 2 serial data circuit shorted to voltage.
- An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit.

TEST DESCRIPTION

Steps 1-5:

Steps 6-9:

Steps 10-11:

Steps 12-13:

Steps 14-15:

Steps 16-18:

Steps 19-21:

Steps 22-25:

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 packs 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 star 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 star 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.