Scan Tool Does Not Communicate With Class 2 Device

Diagnostic Chart (Part 1 Of 4):

Diagnostic Chart (Part 2 Of 4):

Diagnostic Chart (Part 3 Of 4):

Diagnostic Chart (Part 4 Of 4):

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 AIDS
The engine will not start when there is a total malfunction of the class 2 serial data circuit while the engine is not running.

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.
3. The DTC U1300, U1301, and U1305 may be retrieved with a history status. 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 a U1255 with a current status. This indicates that the malfunction occurred when the ignition was on. Any additional DTCs beginning with "U" indicate a specific module is not communicating. The U1XXX test is used to diagnose this concern.
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. An open in the class 2 serial data circuit between the DLC and connector C200 will prevent the scan tool from communicating with any module. This condition will not set a DTC.
8. The class 2 serial data circuit is shorted to voltage or to ground. This step isolates the concern to the five modules not linked through a fuse panel.
9. This step adds the rear fuse panel
11. This step adds the three modules linked through the rear fuse panel.
13. This step adds the modules linked in the engine compartment.
19. The modules in the three loops (base, interior and engine compartment) must be diagnosed in the following order:

Base - body control module (SBM), heater and A/C programmer (HCM), instrument cluster (ICP) and vehicle theft module (VTD) last.

Interior memory seat module (MSM), inflatable restraint sensing and diagnostic (SDM) module and remote function actuator (RFA) last

Engine Compartment - powertrain control module (PCM) first and electronic brake control module (EBCM) second. The connector C101 is diagnosed last.

26. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.
27. The communication malfunction may have prevented diagnosis of the customer complaint.