The drive motor generator battery control module is also referred to as the battery energy control module (BECM). The BECM will diagnose its own systems and determine when a fault condition is present. Diagnostics and system status is communicated from the BECM to the hybrid powertrain control module (HPCM) through serial data. The HPCM is the host controller for diagnostic trouble code (DTC) information.

The drive motor generator battery contains 3 high voltage (HV) contactor relays that allow the HV direct current (DC) batteries to be connected to the vehicle or safely contain the DC high voltage within the drive motor generator battery assembly. The three relays are a positive HV contactor relay, negative HV contactor relay, and the current limit relay. These relays close and open in a specific sequence controlled by the BECM. Both the BECM and the HPCM monitor for proper system operation.

The power-up sequence for the HV DC system occurs in the following order:

1. The BECM performs a precharge test, by closing both the negative and current limit relays. Because the current limit relay routes the HV current through a current limit resistor, the hybrid battery terminal voltage should increase at a steady, predictable rate.
2. When the BECM observes that hybrid battery terminal voltage and hybrid battery calculated voltage are at about the same voltage, the BECM closes the positive contactor relay.
3. With both the negative and positive contactor relays closed, the BECM opens the current limit relay.

The BECM calculates a total hybrid battery voltage based upon internal hybrid battery voltage sense leads. The BECM measures the actual voltage at the hybrid battery terminals and compares this value to the calculated voltage.

The HPCM measures the actual voltage within the drive motor generator power inverter module (PIM) and compares this value to the calculated voltage. The time it takes for terminal voltage to equal hybrid battery calculated voltage is measured and recorded. If the precharge event does not occur as expected, a DTC will set.

If the BECM detects 2 consecutive failed high voltage precharge events, a precharge wait time is activated by the BECM. This precharge wait time limit is to allow the precharge circuit internal to the drive motor generator battery assembly to cool down. The precharge wait time counts down in seconds and is displayed on the scan tool. The contactor relays will not close until the precharge wait time has timed out.

P0C77

P1A20

P0C77

One of the following conditions exist:

P1A20

After waiting 140 milliseconds after the start of precharge, hybrid battery calculated voltage and hybrid battery terminal voltage are still 23 V apart.

The HPCM will not command the HV contactor relays closed.

DTCs P0C77 and P1A20 are type C DTCs.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Drive Motor Battery System Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

1. Verify that DTCs P0A95, P0AC1, P0C76, or P1A07 are not set, and that no HPCM DTCs are set.

⇒	If the specified DTCs are set, diagnose those DTCs first.

2. Verify the 125 A HV fuse in the manual disconnect lever is not open.

⇒	If the fuse is open, refer to DTC P0A95.

Danger: Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

•	Safety glasses with appropriate side shields when within 50 feet of the vehicle, either indoors or outdoors

•	Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors

-	Visually and functionally inspect the gloves before use.

-	Wear the Insulation gloves at all times when working with the high voltage battery assembly, whether the system is energized or not.

Failure to follow the procedure exactly as written may result in serious injury or death.

Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

The High Voltage Disabling procedure will perform the following tasks:

•	Identify how to disable high voltage.

•	Identify how to test for the presence of high voltage.

•	Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.

Failure to follow the procedures exactly as written may result in serious injury or death.
3. Connect the EL-48458 at the drive motor generator power inverter module (PIM). Refer to the EL-48458 installation procedure located in High Voltage System Diagnosis.
4. Ignition ON, attempt to precharge the HV system by moving the HV contactor relay switch on the tester to the closed position. Verify that the hi-voltage circuit LED for hi-voltage greater than 60 V does not illuminate.

⇒	If the LED illuminates, replace the drive motor generator power inverter module.

5. Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling.
6. Remove the EL-48458 . Refer to the removal procedure located in High Voltage System Diagnosis.
7. Inspect and test the HV 300 V positive and negative DC cables and connection points between the drive motor generator battery X1 and X2 connectors and the drive motor generator power inverter module (PIM) assembly X2 and X3 connectors for an open/high resistance condition.

⇒	If an open/high resistance condition is found on the HV cables or connection points, replace the drive motor battery 300 V positive and negative cable.

8. Remove the drive motor generator battery upper cover. Refer to Drive Motor Battery Case Upper Cover, Front Cover, and Right Side Cover Replacement.
9. Inspect and test the HV DC cables and connection points between the terminals listed below for an open/high resistance condition.

•	Negative output terminal X2 and the negative contactor relay terminal X3

•	Positive output terminal X1 and the positive contactor relay terminal X3

•	Negative contactor relay terminal X2 and battery module 1

•	Positive contactor relay terminal X2 and battery module 40

•	Positive contactor relay terminal X3 and the current limit relay terminal 2 X4

⇒	If an open/high resistance condition is found on the HV cables or connection points, replace the appropriate component.

10. Test for 11-13 Ω between terminal 1 X3 at the current limit relay and terminal X2 at the positive contactor relay.

⇒	If not within the specified range, test or replace the current limit resistor.

11. Connect the 12 V battery.
12. Install the HV manual disconnect lever.
13. Command the negative contactor relay closed with a scan tool. Test for less than 0.5 Ω between terminals X2 and X3 of the negative contactor relay.

⇒	If greater than the specified value, test or replace the negative contactor relay.

14. Command the positive contactor relay closed with a scan tool. Test for less than 0.5 Ω between terminals X2 and X3 of the positive contactor relay.

⇒	If greater than the specified value, test or replace the positive contactor relay.

15. Disconnect the X1 harness connector at the negative contactor relay.
16. Test for infinite resistance between the negative contactor relay terminal X2 and terminal X3.

⇒	If less than the specified value, test or replace the negative contactor relay.

17. Ignition OFF, test for less than 5 Ω between the negative contactor relay ground circuit terminal 2 and ground.

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

18. Connect a test lamp between the negative contactor relay control circuit terminal 1 X1 and the ground circuit terminal 2 X1.
19. Command the negative contactor relay open and closed with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the drive motor generator battery control module.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the drive motor generator battery control module.

20. Disconnect the X1 harness connector at the positive contactor relay.
21. Test for infinite resistance between the positive contactor relay terminal X2 and terminal X3.

⇒	If less than the specified value, test or replace the positive contactor relay.

22. Ignition OFF, test for less than 5 Ω between the positive contactor relay ground circuit terminal 2 X1 and ground.

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

23. Connect a test lamp between the positive contactor relay control circuit terminal 1 X1 and the ground circuit terminal 2 X1.
24. Command the positive contactor relay open and closed with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the drive motor generator battery control module.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the drive motor generator battery control module.

25. Disconnect the X1 and X2 harness connectors at the current limit relay.
26. Test for infinite resistance between the current limit relay terminal 1 X3 and terminal 2 X4.

⇒	If less than the specified value, test or replace the current limit relay.

27. Ignition OFF, test for less than 5 Ω between the current limit relay ground circuit terminal 6 X2 and ground.

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

28. Connect a test lamp between the current limit relay control circuit terminal 5 X1 and the ground circuit terminal 6 X2.
29. Command the current limit relay open and closed with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the drive motor generator battery control module.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the drive motor generator battery control module.

30. If all circuits test normal, test or replace the current limit relay and the positive and negative contactor relays.

Positive and Negative HV Contactor Relay Test

Danger: Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

•	Safety glasses with appropriate side shields when within 50 feet of the vehicle, either indoors or outdoors

•	Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors

-	Visually and functionally inspect the gloves before use.

-	Wear the Insulation gloves at all times when working with the high voltage battery assembly, whether the system is energized or not.

Failure to follow the procedure exactly as written may result in serious injury or death.
1. Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling.
2. Remove the drive motor generator battery upper cover. Refer to Drive Motor Battery Case Upper Cover, Front Cover, and Right Side Cover Replacement.
3. Remove the appropriate contactor relay.
4. Test for 20-30 Ω between terminals 1 X1 and 2 X1.

⇒	If not within the specified range, replace the relay.

5. Test for infinite resistance between the following terminals:

•	X2 and 1 X1

•

X2 and X3

•	X2 and 2 X1

•	2 X1 and X3

⇒	If not the specified value, replace the relay.

6. Install a 20 A fused jumper wire between relay terminal 2 X1 and 12 V. Install a jumper wire between relay terminal 1 X1 and ground. Test for less than 2 Ω between terminals X2 and X3.

⇒	If greater than specified range, replace the relay.

Current Limit Relay Test

Danger: Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

•	Safety glasses with appropriate side shields when within 50 feet of the vehicle, either indoors or outdoors

•	Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors

-	Visually and functionally inspect the gloves before use.

-	Wear the Insulation gloves at all times when working with the high voltage battery assembly, whether the system is energized or not.

Failure to follow the procedure exactly as written may result in serious injury or death.
1. Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling.
2. Remove the drive motor generator battery upper cover. Refer to Drive Motor Battery Case Upper Cover, Front Cover, and Right Side Cover Replacement.
3. Remove the current limit relay.
4. Test for 55-75 Ω between terminals 5 X1 and 6 X2.

⇒	If not within the specified range, replace the relay.

5. Test for infinite resistance between the following terminals:

•	1 X3 and 5 X1

•	1 X3 and 2 X4

•	1 X3 and 6 X2

•	6 X2 and 2 X4

⇒	If not the specified value, replace the relay.

6. Install a 20 A fused jumper wire between relay terminal 6 X2 and 12 V. Install a jumper wire between relay terminal 5 X1 and ground. Test for less than 2 Ω between terminals 1 X3 and 2 X4.

⇒	If greater than specified range, replace the relay.

Current Limit Resistor Test

Danger: Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:

•	Safety glasses with appropriate side shields when within 50 feet of the vehicle, either indoors or outdoors

•	Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors

-	Visually and functionally inspect the gloves before use.

-	Wear the Insulation gloves at all times when working with the high voltage battery assembly, whether the system is energized or not.

Failure to follow the procedure exactly as written may result in serious injury or death.
1. Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling.
2. Remove the drive motor generator battery upper cover. Refer to Drive Motor Battery Case Upper Cover, Front Cover, and Right Side Cover Replacement.
3. Remove the current limit resistor.
4. Test for 11-13 Ω across the resistor.

⇒	If not within the specified range, replace the current limit resistor.

Perform the Diagnostic Repair Verification after completing the repair.