Modules connected to the high and low speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.

The enable signal circuit is energized by the body control module (BCM) to activate multiple modules when the BCM determines that communication is required. Some modules may still become active due to their own ignition voltage source if the enable circuit is not functional. The serial data gateway module (SDGM) translates serial data messages between the high speed GMLAN serial data bus, the low speed GMLAN serial data bus, and the high speed hybrid GMLAN serial data bus. Messages between the battery energy control module (BECM) and the other hybrid system control modules must pass thru the SDGM. DTC U1862 is set by the battery energy control module (BECM), but is stored in and reported by the hybrid powertrain control module (HPCM).

A supervised periodic message that includes the SDGM availability has not been received by the BECM.

The charging system will not operate properly and the vehicle battery will discharge as the vehicle is driven. Multiple DTCs may set depending on the fault location and when the fault occurred.

Schematic Reference

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

1. Ignition OFF, disconnect the harness connector X2 at the SDGM.
2. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 1 minute.

Important: The scan tool must be disconnected and the ignition switch OFF for 30 seconds for proper test results.

3. Test for less than 10 ohms between the ground circuit terminal 18 X2 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

4. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 8 X2 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

5. Test for 10.5-12.5 volts between the serial data communication enable circuit and ground.

⇒	If less than the specified range, test the serial data enable circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the applicable communication/control module.

6. Ignition OFF, connect the harness connector X2 to the SDGM.
7. Ignition OFF, disconnect the harness connector X1 at the SDGM.
8. Ignition ON, test for 2.3-2.5 volts between the high speed GMLAN serial data bus low circuit terminal listed below and ground:

•	SDGM terminal 15 X1

•	SDGM terminal 16 X1

⇒	If greater than the specified range, test the serial data bus low circuit for a short to voltage. If the circuit tests normal, replace the applicable communication/control module.

⇒	If less than the specified range, test the serial data bus low circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the applicable communication/control module.

9. If all circuits test normal, replace the SDGM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.