Eaton Fuller Hybrid Transmission Fault Code 108 – High Voltage Battery 1 Control Unit Power Supply

Fault code for Eaton Hybrid Drive Systems models (MY08) EH-8E306A-U, EH-8E306A-UPG, EH-8E306A-UP, EH-8E306A-CD, EH-8E306A-T, EH-6E606B-CD, (MY09) EH-8E406A-U/P, EH-8E406A-UP, EH-8E406A-UPG, EH-8E406A-CD, EH-8E406A-CDG, EH-8E406A-CDR, EH-8E406A-T, EH-6E706B-CD, EH-6E706B-P and EH-6E706B-UPG. Read below to learn how to test, clear and fix fault code errors for your Freightliner, Mack, Peterbilt, Kenworth, Volvo, International, and heavy-duty truck and equipment. The high-voltage batteries are 172 volts each connected in series to produce 340 volts DC. The Battery Control Unit located in the Relay Box receives 12-volts ignition power and ground from the Inverter.

Fault Code 108 – High Voltage Battery 1 Control Unit Power Supply Detection

The following preconditions must be met before the system detects the fault:

  • Hybrid Control Module (HCM) ignition voltage is greater than 7 volts and less than 16 volts.

Note: When troubleshooting an Inactive code refer to the Product Diagnostic Mode (PDM)

Conditions to Set Fault Code Active

  • FMI 3 is set when the BCU detects the ignition voltage is greater than 16 volts for 1 second.
  • FMI 4 is set when the BCU detects the ignition voltage is less than 7 volts for 1 second.

Fallback When Fault Code 108 is set the following conditions occur:

  • Amber “Check Hybrid” light illuminates.
  • Fault is stored in Hybrid Control Module (HCM) memory.
  • Inverter shuts high-voltage system off.
  • HCM continues to control the hybrid vehicle in a diesel-only mode.
  • Transmission defaults start gear to 1st.

Conditions to Set Fault Code Inactive

Only Inactive faults can be cleared from the Transmission Electronic Control Unit (TECU) or HCM history using ServiceRanger. The TECU automatically clears the faults from history after 200 hours and the HCM automatically clears the faults from history after the fault has been Inactive for 200 hours.

This fault code can be caused by any of the following:

  • FMI 3
    • PEC (MY08 Systems)
    • Relay Box (MY09 Systems)
  • FMI 4
    • Relay Box
    • Low-voltage harness from Inverter to Power Electric Carrier (PEC)
    • HCM
    • Low-voltage harness from HCM to Inverter
    • Inverter

Fault Code 108 – High Voltage Battery 1 Control Unit Power Supply Test

Component Identification MY08 Systems:

HCM - Hybrid System Interface Connector

Harness Front View
(HCM – Hybrid System Interface Connector)

Inverter 56-Way Mating Connector View

Delphi 56-Way Mating Connector View
(Inverter – Low Voltage Connector)

PEC - Low Voltage Connector

19 – Way Mating Connector View
(PEC – Low Voltage Connector)

NOTE: Refer to the Eaton Hybrid Component and Connector Location for Connector Locations in MY08 Systems

HCM Inverter PEC connector pins

Component Identification MY09 Systems:

HCM - Hybrid System Interface Connector

Harness Front View
(HCM – Hybrid System Interface Connector)

Duetsch 40-way mating connector view

Duetsch 40-Way Mating Connector View
(Inverter – Low Voltage Connector)

PEC - Low Voltage Connector

19 – Way Mating Connector View
(PEC – Low Voltage Connector)

NOTE: Refer to the Eaton Hybrid Component and Connector Location for Connector Locations in MY09 Systems.

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