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 trouble codes (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, DTC U1300 will be set. Refer to DTC U1300 Class 2 Data Link Low.
- When the class 2 serial data circuit is shorted to B+, DTC U1301 will be set. Refer to DTC U1301 Class 2 Data Link High.

Step 1:

Steps 2 - 5:

Steps 6 - 9:

Steps 10 - 11:

Steps 12 - 14:

Steps 15 - 17:

Steps 18 - 20:

Steps 21 - 24:

Step 25:

Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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:
- The body control module (BCM)
- The electronic brake control module (EBCM)
- The instrument cluster
- The powertrain control module (PCM)/vehicle control module (VCM)
- The supplemental restraint sensing and diagnostic module (SDM)
- The transfer case shift control module (TCSCM)

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. Data link connector terminal 2 and terminal 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 splice pack SP2O1 will prevent the scan tool from communicating with the module. This condition will not set a DTC.
9. The class 2 serial data circuit is shorted to voltage or ground. 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, ensure that there is not a module connected to the wire being tested. This test isolates the BCM class 2 serial data 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/VCM class 2 serial data circuit.
13. This test isolates the EBCM class 2 serial data circuit.
15. This test isolates the SDM class 2 serial data circuit.
17. This test isolates the instrument cluster class 2 serial data circuit.
21. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.
22. The communication malfunction may have prevented diagnosis of the customer complaint.