Scan Tool Does Not Communicate with Class 2 Device (LHD)

SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE (LHD)















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
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 class 2 serial data bus:
-> The audio amplifier (AMP)
-> The dash integration module (DIM)
-> The digital radio receiver (DRR)
-> The driver door module (DDM)
-> The driver door switch assembly (DDSA)
-> The electronic brake control module (EBCM)
-> The engine control module (ECM) for LY7/LP1 models communicates on both class 2 and high speed GMLAN links and communicate with the scan tool on high speed GMLAN
-> The front passenger door module (FPDM)
-> The HVAC control module
-> The inflatable restraint sensing and diagnostic module (SDM)
-> The instrument panel cluster (IPC)
-> The left rear door module (LRDM)
-> The memory seat module (MSM) w/A45
-> The radio
-> The radio antenna module
-> The rear integration module (RIM)
-> The right rear door module (RRDM)
-> The theft deterrent control module (VTD)
-> The TV antenna module
-> The vehicle communication interface module (VCIM)

3. The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
-> U1300
-> U1301
-> U1305

6. A state of health DTC with a history status may be present along with a U1000 code 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.

10. This step takes out from the class 2 bus the modules connected to splice pack SP303, excepting SDM and RIM.

11. This step takes out from the class 2 bus the modules connected to splice pack SP300, excepting IPC.

13. This test isolates the class 2 serial data circuit between DLC and DIM.

18. This test localizes the class 2 serial data circuit of the suspected bus, that is shorted.

22. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.

23. The communication malfunction may have prevented diagnosis of the customer complaint.