Scan Tool Does Not Communicate with CAN Device

SCAN TOOL DOES NOT COMMUNICATE WITH CAN DEVICE
Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition a DTC U2100 will be set. This DTC can be retrieved as history only.

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

TEST DESCRIPTION

Steps 1 - 9:

Steps 10 - 19:

The numbers below refer to the step numbers on the diagnostic table:
2. A partial malfunction in the GMLAN serial data circuits uses a different procedure from a total malfunction of the GMLAN data circuits. The following modules communicate on the GMLAN serial data circuits:
- Engine control module (ECM)
- Transmission control module (TCM)
3. The DTC U2100 may be retrieved with a history status, but is not the cause of the present condition.
6. Data link connector terminals 6 and 14 provide the connection to the GMLAN serial data (+) circuit and the GMLAN serial data (-) circuit respectively.
16. The communication malfunction may have prevented diagnosis of the customer complaint.