Modules connected to the high speed hybrid 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 also, 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 communication enable and the wakeup circuits are energized by a specific module to activate another specific module when the ignition key is in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wakeup circuits. Refer to the schematics to determine which modules activate and are activated using the enable or wakeup circuits.

The motor control module (MCM) 1, 2, and the hybrid powertrain control module (HPCM) are all internal to the drive motor power inverter module (PIM). The MCMs communicate only with the HPCM with the HPCM sending out DTC information to other modules regarding the MCMs. All circuits to the MCM are also internal to the PIM and is replaced as a single component.

Communication diagnostics for the serial data, including module power and ground as well as the wakeup circuits for both MCMs, and the HPCM are all diagnosed from external sources only to the PIM connector because any circuit fault condition within the PIM will cause a complete replacement.

A supervised periodic message that includes the transmitter module availability has not been received.

The modules is never signaled, therefore the specific subsystems will not function.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

1. Verify that DTC B137A is not current in the serial data gateway module (SDGM).

⇒	If the DTC is current in the SDGM, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. Verify that DTC U1815 is not set current only in the HPCM.

⇒	If the DTC is current in the HPCM only, replace the drive motor power inverter module (PIM).

1. Ignition OFF, disconnect the harness connector X1 at the PIM.
2. Test for less than 5 ohms between the PIM case and ground.

⇒	If greater than the specified range, test the ground strap for an open/high resistance. If the circuit tests normal, replace the PIM.

3. Ignition ON, verify that a test lamp illuminates between the following voltage circuit terminals of the PIM and ground.

•	Terminal 6

•	Terminal 7

•	Terminal 20

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

4. Ignition ON, verify that a test lamp illuminates between the signal circuit terminal 19 and ground.

⇒	If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the SDGM.

5. Ignition OFF, disconnect the harness connector X3 at the engine control module.
6. Test for less than 1.0 ohm on the high speed hybrid GMLAN serial data circuits between the following ECM and PIM circuit terminals.

•	ECM X 3 terminal 53 and PIM X 1 terminal 11

•	ECM X 3 terminal 33 and PIM X 1 terminal 10

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

7. If all circuits test normal, replace the PIM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.