P0C77
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 Descriptor
DTC P0C77
-
Hybrid Battery System Precharge Time Too Short
DTC P0C78
-
Hybrid Battery System Precharge Time Too Long
Circuit/System Description
The hybrid battery system voltage is controlled by two high voltage contactors. 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 battery pack assembly. Of the two contactors, one is a pre-charge contactor and the other is the primary contactor. The two contactors are closed in a specific sequence by the starter/generator control module. The pre-charge contactor is closed first. This causes high voltage to flow through the pre-charge resistor, allowing system voltage to build slowly. Once the system voltage has raised and stabilized, the primary contactor is closed. Both contactors are controlled by the starter/generator control module. The starter/generator control module supplies B+ to each contactor at all times. When the contactors are to be closed, the starter/generator control module will provide a ground to the contactor through a low side driver.
Conditions for Running the DTC
P0C77
* No faults are set against the battery current sensor
* No faults are set against the internal bus voltage sensor
* Bus voltage is less than 50% before the start of precharge
P0C78
* No faults are set against the battery current sensor
* No faults are set against the internal battery voltage sensor
* No faults are set against the internal bus voltage sensor
Conditions for Setting the DTC
P0C77
Bus voltage is greater than 95% in less than 75 ms after the start of precharge
P0C78
Bus voltage has not reached 95% in less than 1 second after the start of precharge
OR
Battery current is greater than 5 A for longer than 100 ms after the start of precharge
Action Taken When the DTC Sets
DTCs P0C77 and P0C78 are type B DTCs
Conditions for Clearing the DTC
DTCs P0C77 and P0C78 are type B DTCs
Diagnostic Aids
Some conditions than may cause a too long pre-charge are:
* Pre-charge contactor that is inoperative and does not close
* Excessive resistance in the closed contacts of the pre-charge contactor
* Excessive resistance in the pre-charge resistor
* An open or excessive resistance in any of the high voltage (orange) circuits or terminal supplying voltage to the pre-charge resistor and contactor
Some conditions than may cause a too short pre-charge are:
* Primary contactor or pre-charge contractor stuck in the closed position
* Primary contactor control circuit shorted to ground, causing the primary contactor to remain closed even when not commanded closed by the starter/generator control module
* Too little resistance in the pre-charge resistor
Reference Information
Schematic Reference
Hybrid Energy Storage Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Connector End Views By Name
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 eAssist battery pack assembly will utilize an exchange program. Please consult the most recent revision of bulletin/PI# PIC5520, available in Service Information♦(SI), for a list of approved eAssist battery pack assembly service procedures. Components that may be removed and serviced without exchanging the complete battery pack assembly are identified in the bulletin/PI. Please contact the GM Technical Assistance Center (1-877-446-8227) if you have any questions.
Note:
In High Voltage Disabling High Voltage Disabling , perform the disabling procedure for servicing components within the A4 hybrid/EV battery pack. The C4A hybrid/EV battery section 1 and C4B hybrid/EV battery section 2 will be disconnected as part of the disabling procedure.
1. Ignition OFF, disable high voltage at the A4 hybrid/EV battery pack. Refer to High Voltage Disabling High Voltage Disabling.
2. Disconnect the X1 and X2 harness connectors at the KR134 pre-charge contactor.
3. Connect the 12 V battery, ignition ON.
4. Verify a test lamp illuminates between the B+ circuit terminal A X1 and ground.
• If the test lamp does not illuminate
1. Ignition OFF, disconnect the harness connector at the K59 starter/generator control module.
2. Test for less than 2 ohms in the B+ circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K59 starter/generator control module.
• If the test lamp illuminates
5. Test for less than 1 V between the control circuit terminal A X2 and ground.
• If 1 V or greater
1. Ignition OFF, disconnect the X4 harness connector at the K59 starter/generator control module.
2. Test for less than 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K59 starter/generator control module.
• If less than 1 V
6. Install a 10 A fused jumper wire between the B+ terminal A X1 and 12 V. Install a jumper wire between the control terminal A X2 and ground.
Note:
This step checks the resistance of the closed contactor. Excessive resistance in the closed contacts may cause a slow pre-charge. To verify the resistance, the contactor must be closed. To close the contactor, all terminals at the contactor must be removed and the contactor B+ and control circuits jumpered to B+ and ground. This will close the contacts and allow the resistance of the contacts to be measured.
7. Test for less than 2 ohms between the high voltage terminals of the closed KR134 pre-charge contactor.
• If 2 ohms or greater
Replace the KR134 pre-charge contactor.
• If less than 2 ohms
8. Ignition OFF, connect the X1 and X2 harness connectors at the KR134 pre-charge contactor. Disconnect the X4 harness connector at the K59 starter/generator control module.
9. Test for infinite resistance between the control circuit terminal 6 and ground.
• If less than infinite resistance
1. Ignition OFF, disconnect the X2 harness connector at the KR134 pre-charge contactor
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, test or replace the KR134 pre-charge contactor.
• If infinite resistance
10. Test for 20-40 ohms between the B+ circuit terminal 4 and the control circuit terminal 6.
• If not between 90-115 ohms
1. Ignition OFF, disconnect the X2 harness connector at the KR134 pre-charge contactor.
2. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the KR134 pre-charge contactor.
• If between 20-40 ohms
11. Test for infinite resistance between the control circuit terminal 5 and ground.
• If less than infinite resistance
1. Ignition OFF, disconnect the X1 harness connector at the KR38 main contactor.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, test or replace the KR38 main contactor.
• If infinite resistance
12. Test for infinite resistance between the high voltage terminals of the open KR38 main contactor.
• If not infinite resistance
Replace the KR38 main contactor.
• If infinite resistance
13. Test for 5-10 ohms between the R25 hybrid/EV battery pre-charge resistor terminals.
• If not between 5-10 ohms
Replace the R25 hybrid/EV battery pre-charge resistor.
• If between 5-10 ohms
14. Test each of the high voltage circuits and terminals supplying the R25 hybrid/EV battery pre-charge resistor and KR134 pre-charge contactor for less than 2 ohms end to end.
• If 2 ohms or greater
Replace the appropriate harness.
• If less than 2 ohms
15. Replace the K59 starter/generator control module.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Generator Battery Control Wiring Harness Replacement (B2 to BDU1 Contactor) Generator Battery Control Wiring Harness Replacement (B2 to BDU1 Contactor)Generator Battery Control Wiring Harness Replacement (B1 and B2 to BECM Junction Block) Generator Battery Control Wiring Harness Replacement (B1 and B2 to BECM Junction Block)
* Control Module References Programming and Relearning for starter/generator control module replacement, programming, and setup