Scan Tool Does Not Communicate With Class 2 Device
CIRCUIT DESCRIPTIONModules connected to the class 2 serial data circuit (some are optional) 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
^ The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must be connected to the DLC for any other module to communicate with the scan tool.
^ When the class 2 serial data circuit is shorted to ground, U1300 will be set. Refer to DTC U1300. U1300
^ When the class 2 serial data circuit is shorted to B+, U1301 will be set. Refer to DTC U1301. U1301
TEST DESCRIPTION
Steps 1-10:
Steps 11-17:
Steps 18-24:
Steps 25-32:
Steps 33-40:
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)
^ Powertrain Control Module (PCM)
^ Automatic Transfer Case (ATC)
^ Electronic Brake Control Module (EBCM)
^ Inflatable Restraint Sensing and Diagnostic Module (SDM)
^ Instrument Panel Cluster (IPC)
^ Suspension Control Module (SCM)
^ HVAC Control Module
^ Automatic Transmission
^ Driver Information Center (DIC)
^ Memory Mirror Control Module
^ Memory Seat Control Module
^ OnStar(R)/Cellular Phone line
3. The following DTCs may be retrieved with a history status:
^ U1300
^ U1301
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 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. A poor connection at terminal A would cause this condition but will not set a DTC.
8. An open in the class 2 serial data circuit between the DLC and the star connector will prevent the scan tool from communicating with any module. This condition will not set a DTC.
9. 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. This test isolates the BCM class 2 serial data circuit.
11. This test isolates the PCM class 2 serial data circuit.
13. This test isolates the ATC class 2 serial data circuit.
15. This test isolates the EBCM class 2 serial data circuit.
17. This test isolates the SDM class 2 serial data circuit.
19. This test isolates the IPC class 2 serial data circuit.
21. This test isolates the SCM class 2 serial data circuit.
23. This test isolates the Automatic HVAC class 2 serial data circuit.
25. This test isolates the Automatic Transmission class 2 serial data circuit.
27. This test isolates the Driver Information Center (DIC) class 2 serial data circuit.
29. This test isolates the Mirror Memory Module class 2 serial data circuit.
31. This test isolates the Seat Memory Module class 2 serial data circuit.
33. This test isolates the OnStar(R)/Cellular Phone class 2 serial data circuit.
40. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.