Eaton Fuller Hybrid Transmission Fault Code 68 – Grade Sensor Fault
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 Grade Sensor is an internal component of the Hybrid Control Module (HCM). It calculates the vehicle grade needed for the Hill Start Assist (HSA) feature to function properly. HSA momentarily holds the Service Brakes at launch to allow single-foot pedal operation without the vehicle rolling back.
Fault Code 68 – Grade Sensor Fault Detection
The following preconditions must be met before the system detects the fault:
- Hybrid Control Module (HCM) 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 12 is set when the grade sensor is not Active or present and HSA is enabled in the HCM configuration.
- FMI 13 is set when HSA is enabled in the HCM configuration but the grade sensor has not been calibrated.
- FMI 14 is set when the HCM is equipped with a Grade Sensor, HSA is enabled and the signal from the sensor is out of range.
Fallback When Fault Code 68 is set the following conditions occur:
- Amber “Check Hybrid” light illuminates.
- Fault is stored in Hybrid Control Module (HCM) memory.
This fault code can be caused by any of the following:
- FMI 12
- Incorrect HCM configuration
- HCM
- FMI 13
- Grade Sensor calibration
- Incorrect HCM configuration
- FMI 14
- HCM
- Incorrect HCM mounting to transmission
Fault Code 68 – Grade Sensor Fault Test
Component Identification:

1. Hybrid Control Module (HCM)
2. Nut (3)
3. 38-Way System Connector Plug-in
4. 38-Way Vehicle Connector Plug-in
5. Mounting Plate
NOTE: Refer to the Eaton Hybrid Component and Connector Location for Connector Locations.
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. Verify FMIs present.
- Key on.
- Retrieve Active fault codes and FMIs with ServiceRanger using the 9-Way Diagnostic Connector or manually.
- If FMI 12 is active, go to Step 2.
- If FMI 13 is active, go to Step 3.
- If FMI 14 is active, go to step 4.
STEP 2. Verify HCM configuration.
- Key on.
- Using ServiceRanger view the HCM configuration.
- If HSA configuration is set at “HSA Enabled” and HSA feature is not needed, select “No HSA” from the dropdown box. Save this configuration change by selecting download, then go to Step 5.
- If HSA configuration is set at “HSA Enabled” and HSA feature is needed, HCM must be changed to hardware version 3.7 or higher containing an internal Grade Sensor. Contact Eaton for correct HCM part number information.
STEP 3. Verify Grade Sensor is calibrated.
- Key on.
- Using ServiceRanger, calibrate the Grade Sensor by selecting “Advanced Product” from the main menu.
- Select “Hybrid Control Module.”
- Select “Grade Sensor Calibration” and follow the on-screen instructions:
- If FMI 13 is not Active after calibrating, calibration complete, go to Step 5.
- If FMI 13 is Active after calibrating, contact Eaton at 1-800-826-HELP (4357).
STEP 4. Verify HCM is properly mounted.
- Key on.
- Ensure the HCM is properly mounted to the transmission.
- If HCM is not properly mounted or cap screws are loose, tighten HCM mounting cap screws, then go to Step 5.
- If HCM is properly mounted to the transmission, replace HCM. See the Hybrid Control Module (HCM) Removal and Installation procedure in TRSM2000, then go to step 5.
STEP 5. Verify repair.
- Key off.
- Reconnect all connectors and the 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 68 appears, find error in testing, go to Step 1.
- If a code other than 68 appears, see Fault Code Index List.
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