Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

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 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 seat interface module (SIM) acts as a gateway module between the GMLAN and UART data communication systems. The SIM receives information such as the driver ID from the BCM via the GMLAN, the SIM then processes the data and transmits to the memory seat module (MSM) via a UART data connection.

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

Schematic Reference

Data Communication Schematics

Connector End View Reference

Master Electrical Component List.

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the SIM harness connector.
2. Test for less than 1 ohm between the module ground circuits and ground.

⇒	If greater than 1 ohm, repair the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.

⇒	If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the SIM.

4. Verify that a test lamp illuminates between all ignition voltage circuits and ground.

⇒	If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the SIM for a short to ground. If the circuits test normal, replace the SIM.

5. Ignition ON, verify that a test lamp illuminates between the serial data communication enable circuit OR the accessory wakeup serial data circuit and ground.

⇒	If the test lamp does not illuminate, repair the circuit for an open/high resistance. If the circuits test normal, replace the BCM.

6. Test for less than 1 ohm in the low speed GMLAN serial data circuit between the SIM and the module that displays the DTC.

⇒	If greater than 1 ohm, test the low speed GMLAN serial data circuit for open/high resistance.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.