Diagnostic Instructions
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
Low speed GMLAN serial data
| 1
| 2
| 1
| --
|
1. No communication on any low speed GMLAN module
2. No communication on one or a specific group of low speed GMLAN modules
|
Circuit/System Description
Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than
OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate.
Diagnostic Aids
| • | This test is used for a total low speed GMLAN 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 U0100-U0299 for
diagnostics. |
| • | An open in the low speed GMLAN serial data circuit between modules will only effect the specific modules. This type of failure will set a loss of communication DTC for each module effected, and the other modules will still communicate. Depending
on which module is effected, the vehicle may not start. |
| • | An open between the data link connector (DLC) and the BCM will only effect the communication with the scan tool. The vehicle modules will still communicate, and the vehicle will start. |
| • | Use the DMM MIN/MAX function to capture/locate intermittent conditions. |
| • | The engine will not start when there is a total malfunction of the low speed GMLAN 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. |
Reference Information
Schematic Reference
Data Communication Schematics
Connector End View Reference
Component Connector End Views
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
- Ignition ON, test for less than 3.0 volts between the low speed GMLAN serial data circuit of the DLC and ground.
| ⇒ | If greater than the specified value, test the serial data circuit for a short to voltage. |
- Test for infinite resistance between the serial data circuit of the DLC and ground.
| ⇒ | If less than the specified value, test the serial data circuit for a short to ground. |
- Test for less than 1.0 ohm in the serial data circuit between the BCM and each module.
| ⇒ | If greater than the specified value, test the serial data circuit for an open/high resistance. If the circuit tests normal, replace the affected module. |
- If all circuits test normal and communications can't be established with any module, test the serial data circuit between the BCM and the DLC for an open/high resistance. If the circuit tests normal, replace the BCM.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the repair.
