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 when operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Multiple diagnostic trouble codes (DTCs) may be set due to this malfunction and during this diagnostic procedure. Complete the diagnostic procedure in order to be sure 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, U1301, or U1305 (Generic Short DTC). U1300
^ When the class 2 serial data circuit is shorted to B+, U1301 will be set. Refer to DTC U1300, U1301, or U1305 (Generic Short DTC). U1300
^ Disconnecting modules and turning the ignition switch to RUN may cause DTCs in the vehicle modules. Check for DTCs in each module upon completion of the required repair.

TEST DESCRIPTION

Steps 1-9:

Steps 10-13:

Steps 14-21:

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 serial data circuit. The following modules communicate on the class 2 serial data circuit:
^ Body Control Module (BCM)
^ Electronic Brake Control Module (EBCM)
^ Electronic Suspension Control (ESC)
^ HVAC with CJ2
^ Sensing and Diagnostic Module (SDM)
^ Instrument Panel Cluster (IPC)
^ Driver Door Module (DDM)
^ Passenger Door Module (PDM)
^ Seat Control Module (SCM) with AAB
^ Powertrain Control Module (PCM)
^ Radio
^ Remote Control Door Lock Receiver (RCDLR)
6. A DTC indicating loss of communications with a particular module 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. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
9. A poor connection at the star connectors will cause multiple communication DTCs to set.
10. An open in the class 2 serial data circuit between the DLC and one of the star connectors will prevent the scan tool from communicating with some modules. This condition will cause multiple communication DTCs to set.
11. This test isolates the BCM by using the J 42236 Serial Data Link Tester and a scan tool. The BCM monitors the ignition switch position and sends the appropriate power mode message to other modules. The BCM must be communicating before attempting to diagnose communication DTCs.
12. This test isolates each module on star connector #1 by communicating with each module separately using the J 42236 Serial Data Link Tester and a scan tool.
13. This test isolates each module on star connector #2 by communicating with each module separately using the J 42236 Serial Data Link Tester and a scan tool.
17. If there are no current DTC's that begin with a "U" the communication malfunction has been repaired.
18. The communication malfunction may have prevented diagnosis of the customer complaint.

"For a description of the RPO Code(s) shown in this article or any of the images therein, refer to the RPO Code List found at Vehicle/Application ID". RPO Codes