Scan Tool Does Not Communicate with Class 2 Device

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 data link connector (DLC) allows communication with the modules for diagnostic purposes.

DIAGNOSTIC AIDS
The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication:
- A class 2 serial data circuit shorted to ground
- A class 2 serial data circuit shorted to voltage
- An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit

TEST DESCRIPTION

Steps 1 - 12:

The numbers below refer to the step numbers on the diagnostic table.
3. 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 engine control module (ECM) and the transmission control module (TCM) communicate functionally on both high speed GMLAN and class 2 serial data circuits. The ECM and TCM communicate with the scan tool on high speed GMLAN only. The auxiliary gage center, w/ERG or ERH, is on class 2 serial data bus but doesn't have diagnostic capability. The following modules communicate with the scan tool on the class 2 serial data circuit:
- The audio amplifier (AMP), w/Bose
- The body control module (BCM)
- The electronic brake control module (EBCM)
- The inflatable restraint sensing and diagnostic module (SDM)
- The instrument panel cluster (IPC)
- The memory seat module (MSM) - driver, w/AAB
- The radio
- The remote control door lock receiver (RCDLR)
- The roof/door module (RDM)
4. The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
- U1300
- U1301
- U1305
7. A state of health DTC with a history status may be present along with a U1000 or U1255 code having a current status. This indicates that the malfunction occurred when the ignition was ON.
8. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
11. A poor connection at the DLC terminal of the splice pack SP201 would cause this condition but will not set a DTC.
12. An open or a short in the class 2 serial data circuit between the DLC and splice pack SP201 will prevent the scan tool from communicating with any module. This condition will not set a DTC.