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DTC P0C77 or P0C78

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    • 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. Earth is provided through the case earth. The hybrid/EV powertrain control module 2 supplies earth for the heater transistor through the hybrid/EV powertrain control module 2 case earth.

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 700 ms.

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 earth 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 multi-function 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-circuit 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 being stuck.
    • A short precharge time may be caused by a positive high-voltage contactor being stuck.

Reference Information

Schematic Reference

Hybrid Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Drive Motor Battery System Description

Electrical Information Reference

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

DTC Type Reference

DTC P16F2

Scan Tool Reference

Control Module References for scan tool information

Special Tools

EL-48900 HEV Safety Kit

For equivalent regional tools, refer to Special Tools .

Circuit/System Testing

Danger: High voltage enabling and disabling shall be only performed by High Voltage Qualified Technicians. The procedures for high-voltage enabling/disabling can be found in the service instructions and must be strictly followed at all times. The usage of the Protocol High Voltage Disabling/Enabling is mandatory. The High-Voltage Qualified Technician is responsible for the adherence to the manufacturer's service instructions as well as current national legal regulations.

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

Questions regarding training can be answered by your national training centre.

Danger: Any hybrid/EV battery pack replacement shall be performed by High-Voltage Qualified Technicians only. The replacement procedure can be found in the service instruction and must be strictly followed at all times. The High-Voltage Qualified Technician is responsible for adherence to the manufacturer's service instructions as well as current national legal regulations. If the hybrid/EV battery pack needs to be replaced contact the Technical Assistance Centre for further instructions prior to removal of the battery pack.

  1. Ignition OFF, disable the high voltage at the T6 power inverter module. Refer to High Voltage Disabling .
  2. Test for less than 5 Ω between terminal 5 and terminal 6 of the S15 hybrid/EV battery pack high-voltage manual disconnect lever.
    3. ⇒If greater than 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. Ignition ON, verify that DTC P0AA1, P0AD9, P0ADD, P0AE2, P0AE4, P0AFA, P0D0A, P0D11, P1EBC-P1EBF, P1EC0 or P1EC3-P1EC5 is not set.
    6. ⇒If any DTC is set, refer to 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).
    7. ⇒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. Ignition 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 Ω between the ground circuit terminal 5 and ground.
    9. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  9. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 9 and ground.
    10. ⇒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. Ignition 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. Ignition ON, test for less than 1 V between the control circuit terminal 11 and earth.
    12. ⇒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. Ignition OFF, test for infinite resistance between control circuit terminal 11 and earth.
    13. ⇒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 Ω 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.
    15. ⇒If greater than the specified range, test the control circuit for or open-circuit/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 after completing the repair.

    •  Drive Motor Battery Replacement and Shipping Preparation
    • 300 Volt Battery Positive and Negative Cable Replacement Link to 207100
    • Control Module References for hybrid/EV powertrain control module 2 replacement, programming and set-up
   


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