Diagnostic Instructions
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
Class 2 Serial Data
| 1
| 2¹
| 1
| --
|
Ground (DLC, terminal 5)
| --
| 1
| --
| --
|
¹ An open between the data link connector (DLC) and JX 205, or DLC pin 5 ground will only effect the communication with the scan tool. The vehicle modules will still communicate.
- No communication on any class 2 serial data module
- No communication on a specific class 2 serial data module
|
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. The class 2 serial data circuit uses JX 205 (splice pack comb) as a common connection between some modules and the DLC. DTCs may be set due to this symptom and during this diagnostic
procedure.
Diagnostic Aids
• | This test is used for a total class 2 communication failure. If only 1 module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use
DTC U1001-U1254
for
diagnostics. |
• | The body control module (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. |
• | An open in the class 2 serial data circuit between JX 205 and a module(s) will only effect the specific module(s). This type of failure will set a loss of communication DTC for each module effected, and the other modules will still
communicate. |
• | An open between the data link connector (DLC) and JX 205 will only effect the communication with the scan tool. The vehicle modules will still communicate, and the vehicle will start. |
• | The engine may not start when there is a total malfunction of the class 2 serial data circuit. |
| The following conditions may cause a total loss of low speed GMLAN data communication: |
- | The low speed GMLAN serial data circuit shorted to ground or voltage. |
- | A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuit. |
- | An open in the DLC ground circuit may cause a scan tool loss of communication, while the modules still communicate. |
• | Use the DMM MIN/MAX function to capture/locate intermittent conditions. |
• | When the class 2 serial data circuit is shorted to ground or to voltage, the following DTCs may set: |
Reference Information
Schematic Reference
Data Communication Schematics
Connector End View Reference
Description and Operation
Body Control System Description and Operation
Electrical Information Reference
Scan Tool Reference
Refer to
Control Module References
for scan tool information.
Circuit/System Testing
- Test for less than 1.0 ohm of resistance between the DLC ground circuit terminal 5 and ground.
⇒ | If greater than the specified range, test the ground circuit for open/high resistance. |
- Ignition OFF, disconnect the harness connector (splice pack comb) at JX 205 and JX208. Install a 3-amp fused jumper wire between JX 205 terminal A and terminal B harness side.
- Ignition ON, with a scan tool, attempt to communicate with the heads up display module (HUD). Communication should be available.
⇒ | If no communication, test the serial data circuit for a short to ground, a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
- Install another 3-amp fused jumper wire to JX 205 terminal A, harness side.
- With HUD communications established, use the other end of the jumper wire to connect all other pins, harness side, one at a time and verify that communication remains available to the BCM.
Important: Allow communications for 5 seconds after connecting a module with the jumper to determine if communication is interrupted or not.
⇒ | If communication is interrupted after connecting an individual module at JX 205, test the serial data circuit between JX 205 and the last module connected for a short to ground and short to voltage. If the circuit tests normal, replace
the module that caused no communication. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the repair.