Scan Tool Does Not Communicate With Class 2 Device

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

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
^ When the class 2 serial data circuit is shorted to ground, U1300 will be set. Refer to DTC U1300 Class 2 Data Link Low.
^ When the class 2 serial data circuit is shorted to B+ U1301 will beset. Refer to DTCU13O1 Class2 Data Link High.

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:
^ EBCM
^ Passlock(TM) Module (Domestic)
^ PCM (Diesel)
^ VCM (Gas)
^ VIM (Export)
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 U1OOO 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. This tests for a poor ground circuit or connection.
8. An open in the class 2 serial data circuit between the DLC and splice 5207 will prevent the scan tool from communicating with any module. This condition will not set a DTC.
9. This test isolates the class 2 serial data circuit. When attempting to isolate a particular module, it is necessary to disconnect the other module due to the redundant connection between the two.
17. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.
18. The communication malfunction may have prevented diagnosis of the customer complaint.