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 battery negative voltage, U1300 will be set. Refer to DTC U1300. U1300
^ When the class 2 serial data circuit is shorted to battery positive voltage, U1301 will be set. Refer to DTC U1301. U1301

TEST DESCRIPTION

Steps 1-2:

Steps 3-11:

Steps 12-18:

Steps 19-26:

Steps 27-31:

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:
^ Transfer case shift control module (TCSCM)
^ Electronic brake control module (EBCM)
^ Powertrain control module (PCM)
^ Body control module (BCM)
^ Instrument panel cluster (IPC)
^ Driver information center (DIC)
^ Inflatable restraint sensing and diagnostic module (SDM)
3. The following DTCs may be retrieved with a history status:
^ U1300
^ U1301

These DTCs are not the cause of the present condition.
4. 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.
5. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
7. A poor connection at terminal A would cause this condition but will not set a DTC.
8. An open in the class 2 serial data circuit between the DLC and SP261 will prevent the scan tool from communicating with any module. This condition will not set a DTC.
9. The class 2 serial data circuit is shorted to battery positive voltage or battery negative voltage. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wiring for a short circuit, make sure there is not a module connected to the wire being tested. This test isolates the BCM class 2 serial data circuit.
11. This test isolates the PCM class 2 serial data circuit.
13. This test isolates the TCSCM class 2 serial data circuit.
15. This test isolates the EBCM class 2 serial data circuit.
17. This test isolates the SDM class 2 serial data circuit.
19. This test isolates the IPC class 2 serial data circuit.
21. This test isolates the DIC class 2 serial data link circuit.
23. This test isolates the redundant serial data circuit between the BCM and the PCM.
31. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.