Eaton Fuller Hybrid Transmission Fault Code 88 – CAN Inverter Message (HCM)

Fault code for Eaton Hybrid Drive Systems models (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 Inverter communicates with the Battery Control Unit (BCU) located in the Power Electronics Carrier (PEC) and the Hybrid Control Module (HCM) on the Controller Area Network (CAN) high-speed proprietary data link. The data link is a two wire twisted pair with two 120 ohm resistors located in the link. Fault Code 88 will only be set with Hybrid Control Module (HCM) software level 663 and lower. HCM software 671 and greater will set a fault code 111 for the inverter CAN message fault.

Fault Code 88 – Inverter CAN Message Fault Detection

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

  • HCM ignition voltage is greater than 7 volts and less than 16 volts.
  • HCM CAN data link fault is Inactive.

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

Conditions to Set Fault Code Active

  • FMI 9 is set when the HCM has not received an Inverter message for 30 consecutive message cycles.
  • FMI 2 is only Active in Product Diagnostic Mode (PDM) and sets if 3 consecutive Inverter messages are not received by the HCM.

Fallback When Fault Code 88 is set the following conditions occur:

  • Amber “Check Hybrid” light illuminates.
  • Fault is stored in Hybrid Control Module (HCM) memory.
  • Electric Motor/Generator Assist and Regeneration are disabled; however, the high-voltage relays remain powered.
  • 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 9, 2
    • Inverter
    • CAN Data Link

Fault Code 88 – Inverter CAN Message Fault Test

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

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

HCM inverter connector location

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