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P0C78




DTC P0C77 or P0C78

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors
DTC P0C77
- Hybrid/EV Battery System Precharge Time Too Short

DTC P0C78
- Hybrid/EV Battery System Precharge Time Too Long

Circuit/System Description

The battery energy control module will diagnose its own systems and determine when a fault condition is present. Diagnostics and system status is communicated from the battery energy control module to the hybrid/EV powertrain control module 2 through serial data. The hybrid/EV powertrain control module 2 is the host controller for diagnostic trouble code (DTC) information.

The hybrid/EV battery contains 5 high voltage contactors and 2 transistors. The high voltage contactors allow the high voltage DC batteries to be connected to the vehicle or safely contain the high voltage DC within the hybrid/EV battery pack assembly. The 5 high voltage contactors are a main positive high voltage contactor, main negative high voltage contactor, charge positive high voltage contactor, charge negative high voltage contactor, and multi-function high voltage contactor. The 2 transistors are the precharge transistor and heater transistor. These contactors/transistors close and open in sequence and are controlled by the hybrid/EV powertrain control module 2. The hybrid/EV powertrain control module 2 supplies voltage to the control circuit for the high voltage contactors and precharge transistors. Ground is provided through the case ground. The hybrid/EV powertrain control module 2 supplies ground for the heater transistor through the hybrid/EV powertrain control module 2 case ground.

Conditions for Running the DTC

P0C77
* The main contactors are in precharge mode.
* Battery current sensor has not failed.
* High Voltage bus voltage less than 40 V before the start of precharge.
* Bus voltage sensor has not failed.

P0C78
* Battery voltage sensor has not failed.
* Bus voltage sensor has not failed.

Conditions for Setting the DTC

P0C77

The bus voltage is above 80% of battery voltage in less than 50ms.

P0C78

The bus voltage has not reached 95% of battery voltage in 700ms.

Action Taken When the DTC Sets

* DTC P0C77 and P0C78 are type A DTCs.
* The contactors will be opened.

Conditions for Clearing the DTC

DTC P0C77 and P0C78 are type A DTCs.

Diagnostic Aids

Note: If the high voltage contactors opened while under high current load, replace the drive motor battery wire junction block relay. The following conditions could cause the high voltage contactors to open while under high current load:

* A collision resulting in supplemental inflatable restraint (SIR) deployment.
* A loss of power or ground to the hybrid/EV powertrain control module 2 while the vehicle is moving.

The precharge time can be affected by the following:

* A long precharge time may be caused by a stuck open hybrid/EV battery negative or hybrid/EV battery multifunction contactor.
* A long precharge time may be caused by a stuck ON hybrid/EV battery precharge transistor.
* A long precharge time may be caused by a short on the propulsion bus preventing the main bus from reaching its target voltage.
* A short precharge time may be caused by a hybrid/EV battery positive high voltage contactor stuck.
* A short precharge time may be caused by a positive high voltage contactor stuck.

Reference Information
Schematic Reference

Hybrid Energy Storage Schematics Hybrid Energy Storage Schematics
Connector End View Reference

Component Connector End Views Hybrid/EV Battery Pack X1
Description and Operation

Drive Motor Battery System Description Drive Motor Battery System Description
Electrical Information Reference

* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference

Control Module References Programming and Relearning for scan tool information
Special Tools

EL-48900 - HEV Safety Kit

For equivalent regional tools, refer to Special Tools Tools and Equipment.

Circuit/System Testing

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.


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


* Safety glasses with appropriate side shields when within 15 meters (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 with leather protectors at all times when working with the high voltage battery assembly, whether the system is energized or not.


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


Danger: The Volt Battery Pack will utilize an exchange program. Please consult the most recent revision of bulletin/PI #PIP4841, available in Service Information (SI), for a list of approved Volt Battery Pack service procedures. Components that may be removed and serviced without exchanging the complete battery pack are identified in the bulletin/PI. Please contact the GM Technical Assistance Center (1-877-446-8227) if you have any questions.


1. Vehicle OFF, disable the high voltage at the T6 power inverter module. Refer to High Voltage Disabling High Voltage Disabling.
2. Test for less than 5 ohm between terminal 5 and terminal 6 of the S15 hybrid/EV battery pack high voltage manual disconnect lever.

• If greater the specified range, replace the S15 hybrid/EV battery pack high voltage manual disconnect lever.

3. Reconnect the S15 hybrid/EV battery pack high voltage manual disconnect lever.
4. Connect the 12 V battery.
5. Vehicle in Service Mode, verify that DTC P0AA1, P0AD9, P0ADD, P0AE2, P0AE4, P0AFA, P0D0A, P0D11, P1EBC-P1EBF, P1EC0, or P1EC3-P1EC5 is not set.

• If any DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

6. With a scan tool, verify the Hybrid Battery Pack Voltage parameter is greater than 205 V at 21°C (69.8° F).

• If the test result is less than the specified range, replace the A4 hybrid/EV battery pack.

7. Disconnect the X2 harness connector at the A28 hybrid/EV battery contactor assembly.
8. Vehicle OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10 ohm between the ground circuit terminal 5 and ground.

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

9. Vehicle in Service Mode, verify that a test lamp illuminates between the B+ circuit terminal 9 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, replace the A4 hybrid/EV battery pack.

10. Vehicle OFF, disconnect the X1 harness connector at the A28 hybrid/EV battery contactor assembly and the X1 harness connector at the K114B hybrid/EV powertrain control module 2.
11. Vehicle in Service Mode, test for less than 1 V between the control circuit terminal 11 and ground.

• If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the K114B hybrid/EV powertrain control module 2.

12. Vehicle OFF, test for infinite resistance between control circuit terminal 11 and ground.

• If less than the specified value, test the control circuit for a short to ground. If the circuit tests normal, replace the K114B hybrid/EV powertrain control module 2.

13. Disconnect the X1 harness connector at the K114B hybrid/EV powertrain control module 2.
14. Test for less than 2 ohm in the control circuit end to end between terminal 11 X1 harness connector at the A28 hybrid/EV battery contactor assembly and terminal 8 X1 harness connector at the K114B hybrid/EV powertrain control module 2.

• If greater than the specified range, test the control circuit for or open/high resistance.

15. If all circuits test normal, replace the K114B hybrid/EV powertrain control module 2. If the DTC resets, replace the A4 hybrid/EV battery pack.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Drive Motor Battery Replacement and Shipping Preparation Procedures
* Battery Cable Replacement (Terminal to Battery 1) Battery Cable Replacement (Terminal to Battery 1)Battery Cable Replacement (Battery 2 to Battery 3) Battery Cable Replacement (Battery 2 to Battery 3)Battery Cable Replacement (Battery 3 to Battery 4) Battery Cable Replacement (Battery 3 to Battery 4)Battery Cable Replacement (Terminal to Battery 4) Battery Cable Replacement (Terminal to Battery 4)
* 300-Volt Battery Positive and Negative Cable Replacement (Drive Motor Battery-to-Inverter ) 300-Volt Battery Positive and Negative Cable Replacement (Drive Motor Battery-to-Inverter )300-Volt Battery Positive and Negative Cable Replacement (Inverter-to-Compressor/Heater Module) 300-Volt Battery Positive and Negative Cable Replacement (Inverter-to-Compressor/Heater Module)300-Volt Battery Positive and Negative Cable Replacement (Drive Motor Battery-to-Charger) 300-Volt Battery Positive and Negative Cable Replacement (Drive Motor Battery-to-Charger)300-Volt Battery Positive and Negative Cable Replacement (Drive Motor Battery-to-APM Module) 300-Volt Battery Positive and Negative Cable Replacement (Drive Motor Battery-to-APM Module)
* Control Module References Programming and Relearning for hybrid/EV powertrain control module 2 replacement, programming and setup

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