Eaton Fuller Hybrid Transmission Fault Code 125 – APG Unit 1 Over Temperature

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 Auxiliary Power Generator (APG) is a 5kW/5kVA DC/AC inverter connected to the high-voltage DC bus of the Eaton hybrid electric vehicle system. It generates 60 Hz single-phase 120V AC power for utility applications. Fault Code 125 sets when the heat sink temperature exceeds the upper-temperature limit for normal operation.

Fault Code 125 – APG Unit 1 Over Temperature Detection

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

  • APG Inverter needs to be operating.

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

Conditions to Set Fault Code Active

  • FMI 0 is set when the heat sink temperature at an unspecified module exceeds the upper-temperature limit for normal operation.

Fallback When Fault Code 125 is set the following conditions occur:

  • Amber “Check Hybrid” light illuminates.
  • Fault is stored in Hybrid Control Module (HCM) memory.
  • APG shuts down if operating.

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 0
    • Cooling System
    • APG Temperature Sensor fault in range

Fault Code 125 – APG Unit 1 Over Temperature Test

STEP 1. Check for Active and Inactive fault code status.

  1. Review and follow the Warnings & Cautions.
  2.  Retrieve Active fault codes and FMIs with ServiceRanger using the 9-Way Diagnostic Connector or manually.
  3. Key off.
    Danger: See High-Voltage Service Shutdown and Power-Up Procedures. Follow the procedures to avoid shock, burn or death from improperly handled high-voltage.
  4. Which FMIs are present?
    • If FMI 0 is Active go to Step 2.

STEP 2. Verify proper coolant level.

  1. Observe the coolant level after the system has cooled to see if it is filled to the proper level.
    • If the coolant is within the recommended limits, replace the Auxiliary Power Generator (APG) Inverter, then go to Step 3.
    • If the coolant is below the recommended limits, refer to OEM for coolant type and fill procedure. Go to Step 3.

STEP 3. Verify repair.

  1. Key off.
  2. Reconnect all connectors.
    Danger: See High-Voltage Service Shutdown and Power-Up Procedures. Follow the procedures to avoid shock, burn or death from improperly handled high-voltage.
  3.  Key on.
  4. Operate the APG and attempt to reset the code.
  5. Clear codes, see  Clear Inactive Faults.
  6. Drive the vehicle and attempt to reset the code.
  7. Check for codes, see View Active and Inactive Faults.
    • If no codes, test is complete.
    • If fault Code 125 appears, find error in testing, go to Step 1.
    • If a code other than 125 appears, see Fault Code Index List.

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