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 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

Steps 1-5:

Steps 6-13:

Steps 14-22:

Steps 23-30:

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 3 modules linked through the rear fuse panel.
13. This step adds the modules linked in the engine compartment.
19. The modules in the 3 loops (base, interior and engine compartment) must be diagnosed in the following order:

Base - Body Control Module (BCM), Instrument Panel Integration Module (IPM), Instrument Panel Cluster (IPC) and theft deterrent control module last.

Interior - Memory Seat Module (MSM), Inflatable Restraint Sensing And Diagnostic (SDM) module and Remote Control Door Lock Receiver (RCDLR) 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.