Scan Tool Does Not Communicate with Low Speed GMLAN Device

SCAN TOOL DOES NOT COMMUNICATE WITH LOW SPEED GMLAN DEVICE

Modules connected to the low speed GMLAN serial data circuits monitor for serial data communications on the low speed GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition, DTC U2100 will be set. These DTCs can be retrieved as history only.

DIAGNOSTIC AIDS
The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuits while the engine is not running. The following conditions may cause a total loss of low speed GMLAN data communication:
- Any of the low speed GMLAN serial data circuits shorted to ground or voltage
- A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuits

TEST DESCRIPTION

Step 1 - Step 8:

Step 9 - Step 18:

The numbers below refer to the step numbers on the diagnostic table.
2. A partial malfunction in the low speed GMLAN serial data circuits uses a different procedure from a total malfunction of the low speed GMLAN data circuits.
3. The DTC U2100 may be retrieved with a history status, but is not the cause of the present condition.
7. Data link connector terminal 1 provides the connection to the GMLAN serial data low circuit and the GMLAN serial data low circuit respectively.
16. The communication malfunction may have prevented diagnosis of the customer complaint.