Scan Tool Does Not Communicate With Class 2 Device

CIRCUIT DESCRIPTION
Modules connected to the class 2 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 circuit is shorted to battery negative voltage, U1300 will be set. Refer to DTC U1300. U1300
^ When the class 2 circuit is shorted to battery positive voltage U1301 will be set. Refer to DTC U1301. U1301

TEST DESCRIPTION

Steps 1-10:

Steps 11-17:

Steps 18-25:

Steps 26-35:

The numbers below refer to the step numbers on the diagnostic table.
2. A partial malfunction in the class 2 circuit uses a different procedure from a total malfunction of the class 2 circuit. The following modules communicate on the class 2 circuit:
^ Electronic climate control module (ECCM)
^ Transfer case shift control module (TCSCM)
^ Electronic brake control module (EBCM)
^ Powertrain control module (PCM)
^ Vehicle interface unit (VIU)
^ Body control module (BCM)
^ Instrument panel cluster (IPC)
^ Driver information center (DIC)
^ Memory seat module (MSM)
^ Inflatable restraint sensing and diagnostic module (SDM)
3. The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
^ U1300
^ U1301
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. DLC 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 circuit between the DLC and SP201 will prevent the scan tool from communicating with a module. This condition will not set a DTC.
9. The class 2 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 wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the BCM class 2 circuit.
11. 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 any other module to communicate with the scan tool. This test isolates the PCM class 2 circuit.
13. This test isolates the TCSCM class 2 circuit.
15. This test isolates the VIU class 2 circuit.
17. This test isolates the EBCM class 2 circuit.
19. This test isolates the SDM class 2 circuit.
21. This test isolates the IPC class 2 circuit.
23. This test isolates the MSM class 2 circuit.
25. This test isolates the DIC class 2 circuit.
27. This test isolates the ECCM class 2 circuit.
31. If there are no current DTCs that begin with a "U," the communication malfunction has been repaired.
32. The communication malfunction may have prevented diagnosis of the customer complaint.