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
Warnings & Cautions
Danger: Danger indicates you will be severely injured or killed if do not follow the indicated procedure.
Warning: Warning indicates an immediate hazard, which could result in severe personal injury if you do not follow the indicated procedure.
Caution: Caution indicates vehicle or property damage could occur if you do not follow the indicated procedure.
Note: Note indicates additional detail that will aid in the diagnosis or repair of a component/system.
Follow the specified procedures in the indicated order to avoid personal injury:
1. If the high-voltage cones are around the vehicle and the lockout is installed on the PEC, the only person that should be allowed to start the vehicle is the person who signed the lockout tag.
2. Before working on a vehicle or leaving the cab while the engine is running, you should place the shift lever in “N” set the parking brake, and block the wheels.
3. For safety reasons, always engage the service brakes prior to selecting gear positions from “N.”
4. Before starting a vehicle always be seated in the driver’s seat, select “N” on the shift control, and set the parking brakes.
5. In vehicles with ePTO, the engine and/or
Motor/Generator can start in ePTO mode. Never perform any maintenance or work on vehicle, while in this mode.
6. 12-Volt Battery positive (+) and negative (-) must be disconnected prior to any welding on any Hybrid equipped vehicle.
Caution: Follow the specified procedures in the indicated order to avoid equipment malfunction or damage.
Caution: Do not release the parking brake or attempt to select a gear until the air pressure is at the correct level.
Caution: To avoid damage to the transmission during towing place the shift lever in “N” and lift the drive wheels off the ground or disconnect the driveline.
High-Voltage Warnings & Cautions
- Use CO2 or Dry Chemical Fire Extinguishers.
- The high-voltage wiring is covered in orange insulation or convoluted tubing and marked with warning labels at the connectors.
- All Eaton® Hybrid Diesel/Electric vehicles will be marked ‘Hybrid’ on the outside of the vehicle, along with the shift label on the dash.
- Refer to OEM for specific location of chassis mounted hybrid components.
- Do NOT cut into the orange high-voltage cables.
- Do NOT cut into or open the PEC.
- Do NOT cut into or open the DC/DC Converter.
- Do NOT cut into or open the Inverter.
A buffer zone must be set up and high-voltage insulated rubber gloves (class 0 with leather protectors) are required prior to working on high-voltage. Failure to follow these instructions may result in severe personal injury or death.
The rubber-insulated gloves that must be worn while working on the high-voltage system are class 0 with leather protectors. The rubber gloves should be tested before EVERY use following the rubber insulation gloves testing procedure found in “Diagnostic Tools/Service Publications” on page 6. Failure to follow these instructions may result in severe personal injury or death.
Before inspecting or working on any high-voltage cables or components the “High-Voltage Service Shutdown and Power-Up Procedure” on page 4 should be followed. Failure to follow these instructions may result in severe personal injury or death.
The Lockout and Tagout devices should only be removed by the technician that placed the Lockout and Tagout devices on the vehicle. Failure to follow these instructions may result in severe personal injury or death.
High-voltage rubber insulated gloves (class 0 with leather protectors) must be worn when working on any
high-voltage cables. The “High-Voltage Service Shutdown and Power-Up Procedure” on page 4 must be followed prior to removing any high-voltage cables. Failure to follow these instructions may result in severe personal injury or death.
High-voltage cables and wiring are orange and contain a warning label at the connectors. High-voltage components are marked with a label. High-voltage rubber insulated gloves (class 0 with leather protectors) must be used when working on any of these components. Failure to follow these instructions may result in severe personal injury or death.
High-Voltage Service Shutdown Procedures
1. Follow “High-Voltage Work Area” procedure.
2. Locate the red PEC Service Switch on the front of the PEC and push switch off.
3. Remove the Service Switch Cover and install the Lockout Bracket (J48506).
4. Fasten tag to the Lockout Bracket.
5. Ensure the PEC Service Switch can not move from the off position.
6. Allow the system to set for a minimum of 5 minutes to discharge high voltage.
7. Connect ServiceRanger and view the Data Monitor PID 116 called “High-Voltage Battery Potential.” Use SPN 520323 for J1939 connection “Battery Voltage RB” (Relay Box).
8. The voltage should be 30 volts or less. If the voltage is above 30 volts, do not work on the vehicle and contact Eaton® at 1-800-826-HELP (4357).
9. Turn ignition key off and proceed to repair or troubleshooting step.
Note: The voltage drops to zero when the key is off.
High-Voltage Service Power-Up Procedure
1. Install all high-voltage connectors into their locked positions.
2. If you are the person working on the vehicle, remove the Lockout Bracket and tag.
3. Reinstall the Lockout Bracket over the Service Switch.
4. Pull the Service Switch out and let vehicle set for 2 minutes.
5. Start vehicle when appropriate.
Eaton Hybrid Component and Connector Location

Eaton Hybrid Component and Connector Location MY09 Systems

STEP 1. Check for fault code status and continuity of Motor/Generator Temperature Sensor circuit
- Retrieve Active fault codes and FMIs with ServiceRanger using the 9-Way Diagnostic Connector.
- 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).
- Is Fault Code 64 also Active?
- Yes, go to Fault Code 64 – ECA Fault.
- No, go to #4.
- 1. Is Fault Code 27 FMI 13 Active?
- If Fault Code 27 FMI 13 is Active, see Fault Code 27 – Clutch Disengagement.
- If Fault Code 27 FMI 13 is Inactive, go to Step 2.
STEP 2. Verify operation of the clutch.
- Key on.
- Start engine.
- 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.
- Key off.
- Reconnect all connectors and negative battery cable.
- Key on.
- Clear codes, see Clear Inactive Faults.
- Drive the vehicle and attempt to reset the code.
- 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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