Scan Tool Does Not Communicate With Class 2 Device

CIRCUIT OPERATION
Modules connected to the Class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating 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
^ The BCM detects that the ignition switch is ON and sends the appropriate power mode message to the other modules connected to the class 2 serial data circuit. The BCM must be connected to the class 2 serial data circuit for many other modules to communicate with the scan tool.
^ If the class 2 serial data circuit was shorted to B+ a history U1301 will set in the modules. Refer to DTC U1301 U1301
^ If the class 2 serial data circuit was shorted to ground is present a history U1300 will set in the modules. Refer to DTC U1300 U1300
^ If the malfunction is intermittent refer to Testing for Intermittent and Poor Connections and Connector Repairs in Diagrams.

TEST DESCRIPTION

Steps 1-5:

Steps 6-18:

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:
^ PCM
^ RIM (W/W8Y)
^ Radio (WO/W8Y)
^ Cellular Telephone (WO/W8Y)
^ OnStar(R) VIU (W/W8Y).
3. DTCs U1300 and/or U1301 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 indicates 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. The Class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wiring for a short, make sure there is not a module connected to the wire being tested.
8. Since the short is not in the wiring harness the malfunction is due to one of the modules.
14. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.
15. The communication malfunction may have prevented diagnosis of the customer complaint.

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