Eaton Fuller Hybrid Transmission Fault Code 74 – Engine Failed to Respond (TECU)

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 Transmission Electronic Control Unit (TECU) communicates with the Electronic Control Unit (ECU) over the J1939 data link during normal operation; however, engine control is accomplished by the ECU during hybrid mode. The TECU changes mode to AutoShift Only or AutoShift Fallback mode. Then the TECU requests changes in engine speed and torque instead of the Hybrid Control Module (HCM).

Fault Code 74 – Engine Failed to Respond (TECU) Detection

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

  • TECU ignition voltage is greater than 7 volts and less than 16 volts.
  • J1939 Communication Link Fault (TECU) Inactive.
  • J1939 Engine Message Fault (TECU) Inactive.
  • J1939 engine speed is greater than 300 RPM if the TECU is in speed control mode, or greater than 1000 RPM if the TECU is in torque control mode.
  • Desired engine speed is less than J1939 engine configuration map speed.

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

Conditions to Set Fault Code Active

  • FMI 7 is set when the difference between actual engine percent torque and desired engine percent torque is greater than 50 for 2 continuous seconds
  • When the difference between desired engine speed and actual engine speed is greater than 400 RPM for four continuous seconds.

Fallback When Fault Code 74 is set the following conditions occur:

  • Fault is stored in TECU memory.
  • If the fault sets while driving, the vehicle remains in the current gear position. Once the vehicle stops, start and reverse gears can be engaged.
  • TECU changes to “AutoShift Fallback” mode.

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 7
    • Engine
    • Fuel system
    • Exhaust back pressure
    • Turbo charger
    • Air Intake/filter restriction
    • Unreported engine loads
    • Incorrect engine configuration settings for transmission assembly

Fault Code 74 – Engine Failed to Respond (TECU) Test

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