• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Class 2 Serial Data | 1 | 2 | 1 | -- |
Ground (DLC) | -- | 1 | -- | -- |
|
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.
• | 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. |
• | An open in the class 2 serial data circuit between JX 203 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. |
• | 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. |
• | When the class 2 serial data circuit is shorted to ground or to voltage, the following DTCs may set: |
- | U1300 |
- | U1301 |
- | U1305 |
Data Link Communications Description and Operation
Control Module References for Scan Tool Information
⇒ | If greater than the specified range, test the ground circuit for open/high resistance. |
⇒ | If no communication, test the serial data circuit for a short to ground, a short to voltage or an open/high resistance between the SDGM and the DLC. If the circuit tests normal, replace the SDGM. |
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 203, test the serial data circuit between JX 203 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. |
Perform the Diagnostic Repair Verification after completing the repair.
• | Control Module References for module replacement, setup, and programming |