Eaton Fuller Hybrid Transmission Fault Code 26 – Clutch Slip

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. The mechanical clutch assembly is controlled through the Electric Clutch Actuator (ECA) which is mounted on the clutch housing. The Hybrid Control Module (HCM) controls the ECA position and monitors several variables to determine if there is a slip concern in the clutch when it is in the closed position.

Fault Code 26 – Clutch Slip 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.
  • ECA ignition voltage is greater than 7 volts and less than 16 volts.
  • There is no Active fault code 18 , 19 or 87 present.

Conditions to Set Fault Code Active

  • FMI 10 is set when the gear position is not neutral, the clutch is in the engaged position and the difference between the transmission Input Shaft Speed Sensor and the engine speed is greater than 150 RPM for 1 second or longer.
  • FMI 23 is set when the HCM detects a clutch overheat situation.
    Note: A “CA” appears if the clutch is allowed to slip and create heat beyond a set point. Do not use the throttle as a hill hold device as it causes clutch damage and a CA.

Fallback When Fault Code 26 is set the following conditions occur:

  • Red “Stop Hybrid” light or amber “Check Hybrid” light illuminates.
  • Fault is stored in HCM memory.

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 10
    • Clutch Assembly
  • FMI 23

Fault Code 26 – Clutch Slip Test

STEP 1. Check for fault code status and continuity of Motor/Generator Temperature Sensor circuit

  1.  Retrieve Active fault codes and FMIs with ServiceRanger using the 9-Way Diagnostic Connector.
  2. Which FMIs are present?
    • If FMI 10 is listed, go to #3.
    • If FMI 23 is listed, FMI 23 is set due to excessive clutch heat. This can occur when the throttle is being used as a hill hold or a worn clutch is slipping on long/steep grades. Contact Eaton at 1-800-826-HELP (4357).
  3. Is Fault Code 64 also Active?
    • Yes, go to Fault Code 64 – ECA Fault.
    • No, go to #4.
  4. 1. Is Fault Code 27 FMI 13 Active?

STEP 2. Verify operation of the clutch.

  1. Key on.
  2. Start engine.
  3. Drive the vehicle under load in highest gear possible. At a steady speed, quickly and fully press and hold the throttle:
    • If Fault Code 26 is Active, replace the Clutch. See CLMT-0365 for installation procedures. Go to Step 3.
    • If Fault Code 26 is Inactive, test is complete. Go to Step 3.

STEP 3. Verify repair.

  1. Key off.
  2.  Reconnect all connectors and negative battery cable.
  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 26 appears, find error in testing, go to Step 1.
    • If a code other than 26 appears, see Fault Code Index List.

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