The engine control module (ECM) performs a rationality check for the voltage sensor located internal to the battery energy control module (BECM) by comparing the pack power electronics bus, and module voltages. If the SGCM diagnostic causes the contactor open, this DTC could set falsely.

The engine is running.

Hybrid system is inactive.

Voltage difference between the battery pack and the average of the battery pack and the power electronics bus returns below the calibrated threshold.

If the SGCM diagnostic causes the contactor open, this DTC could set falsely.

Possible 36 volt cable open circuit between starter/generator control module (SGCM) and BECM.

Schematic Reference

Hybrid Energy Storage Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Generator Battery Carrier Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 35616 GM Approved Terminal Test Kit

Warning: To help avoid personal injury, additional precautions must be taken prior to working on the generator control module or the generator starter. After removing the 36V battery cables from the generator battery, remove both engine wiring harness connectors from the generator control module. Wait at least 5 minutes and then remove the generator control module cover. Verify voltage levels at all 36V, 12V, and 3-phase connections, are less than 3 volts using a DMM before proceeding.

Warning: To help avoid personal injury, be careful when working in the vicinity of the generator battery disconnect control module. Internal components will still be live, 36V potential, even when the cover has been opened or removed.

Note: In order to avoid damaging BECM X1 and X2 connector terminals, the proper test probes should be used. The proper test probes are as follows:

1. If other DTCs are set diagnose those first.
2. If the DTC is still set as current and the contactor status is closed.
3. Scan and record the total pack and module voltages.
4. Remove the generator battery disconnect control module cover. Refer to Hybrid Battery Service Disconnect/Connect
5. Measure the 1, 2, 3 module voltages and then the total pack voltage.

⇒	If any measured voltages differ than 0.5 volt than the scanned voltage, test the voltage sensing harness for a short to ground or an open/high resistance.

6. Disconnect BECM connector X1.
7. Test for 1400-1800 ohms between the following circuits.

•	X1 terminal 12 and Generator Battery 3-X2

•	X1 terminal 2 and Generator Battery 2-X2

•	X1 terminal 11 and Generator Battery 1-X2

•	X1 terminal 1 and Generator Battery 1-X1

⇒	If not within specified range, replace the voltage sensing harness assembly.

8. If all circuits tests normal, replace BECM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.