For 1990-2009 cars only
Diagnostic Instructions
| • | 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. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Class 2 Serial Data | 1 | 2 | 1 | -- |
Ground (DLC) | -- | 1 | -- | -- |
| ||||
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
| • | 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 |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for Scan Tool Information
Circuit/System Testing
- Test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
- Ignition OFF, disconnect the harness connector (splice pack comb) at JX 203. Install a 3-amp fused jumper wire between JX 203 terminal A and terminal C, harness side.
- Ignition ON, with a scan tool, attempt to communicate with the serial data gateway module (SDGM). Communication should be available.
- Install another 3-amp fused jumper wire to JX 203 terminal A, harness side.
- With SDGM communications established, use the other end of the jumper wire to connect all other terminals, harness side, one at a time and verify that communication remains available to the BCM.
| ⇒ | 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. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
| • | Control Module References for module replacement, setup, and programming |
