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

Step 1 - Step 11:

Step 12 - Step 21:

Step 22 - Step 24:

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.