The engine control module (ECM) monitors the hybrid battery pack voltage to detect if the voltage is lower than will allowed to close the contactor.

The engine is running or the ignition is ON, and the battery current is less than 5A.

Minimum pack voltage is less than 22 volts under a no load condition for 3 seconds.

The hybrid system is disabled.

Hybrid battery pack voltage is greater than 22 volts. The hybrid system will still be disabled until the vehicle is restarted.

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

1. Using the scan tool, clear the DTC.
2. Ignition ON, observe and record the scan tool Hybrid Battery 1, Hybrid Battery 2, and Hybrid Battery 3 voltage parameters in the battery energy control module (BECM) data list.
3. Engine ON, road test vehicle while observing the voltage parameters. The voltage should be greater than 22 volts and increase as the vehicle is driven.

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.

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.

Important:  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. Gain access to the battery pack. Refer to Hybrid Battery Service Disconnect/Connect.
2. Measure voltage across the battery pack modules. The voltage should be greater than 22 volts.

⇒	If less than specified value, replace the battery pack.

3. Disconnect BECM connector X1.
4. Test for 1.3-1.7k 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 sensor harness assembly.

5. If all circuits test normal, replace the BECM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.