Eaton Fuller Hybrid Transmission Fault Code 127 – APG Unit 1 Ambient Air 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 that is connected to the high voltage DC bus of the Eaton Hybrid electric vehicle system, and generates 60 Hz single-phase 120-volt AC power for utility applications. The ambient air temperature is measured with an internal sensor and sets a fault when the temperature reaches 140 °F (60 °C).

Fault Code 127 – APG Unit 1 Ambient Air Over Temperature Detection

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

  • HCM is powered and 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 0 is set when the ambient temperature inside of the APG Inverter case reaches 140 °F (60 °C).

Fallback When Fault Code 127 is set the following conditions occur:

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

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
    • Faulty Sensor
    • Ambient case temperature too high

Fault Code 127 – APG Unit 1 Ambient Air Over Temperature Test

STEP 1.Verify Active or 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 present, go to Step 2.

STEP 2. Verify proper coolant level.

  1. Ensure that the Inverter cabinet is not exposed to an external heat source.
  2. 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. Recconect 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. Clear codes, see  Clear Inactive Faults.
  5. Drive the vehicle and attempt to reset the code.
  6. Check for codes, see View Active and Inactive Faults.
    • If no codes, test is complete.
    • If fault Code 127 appears, find error in testing, go to Step 1.
    • If a code other than 127 appears, see Fault Code Index List.

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