Diagnostic Aids
- Use the Data Link References to identify the low speed GMLAN serial data modules.
- 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 U2105-U2199 for diagnostics.
- An open in the low speed GMLAN serial data circuit between the splice pack 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. Depending on which module is effected, the vehicle may not start.
- An open between the data link connector (DLC) and the splice pack 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.