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
When the class 2 serial data circuit:
^ Is shorted to ground
^ Is shorted to voltage
^ Opens

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

Refer to DTC U1300, U1301, or U1305. U1300

TEST DESCRIPTION

Steps 1-4:

Steps 5-14:

Steps 15-20:

The numbers below refer to the step numbers 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 circuit. The following modules communicate on the class 2 serial data circuit:
^ The electronic brake control module (EBCM)
^ The powertrain control module (PCM)
^ Vehicle theft deterrent (VTD)
3. The following DTCs may be retrieved with a history status, but 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 having a current status. This indicates that the malfunction occurred when the ignition was ON.
7. DLC terminal 2 and terminal 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
9. A poor connection at terminal A would cause this condition but will not set a DTC.
10. An open in the class 2 serial data circuit will prevent the scan tool from communicating with the module. This condition will not set a DTC.
11. This test isolates the PCM class 2 serial data circuit.
12. This test isolates the EBCM class 2 serial data circuit.
13. This test isolates the VTD class 2 serial data circuit.
16. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.
17. The communication malfunction may have prevented diagnosis of the customer complaint.