Eaton Fuller Hybrid Transmission Fault Code 56 – Input Shaft Speed Sensor

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 and International truck. The Input Shaft Speed Sensor is located on the 6-bolt PTO Cover, which is standard on the right side of the transmission. The sensor is a magnetic pickup that produces an AC voltage as the countershaft gear teeth moves past the end of the sensor. At idle the speed sensor output is low and increases as the speed of the countershaft increases.

Fault Code 56 – Input Shaft Speed Sensor Detection

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

  • Transmission Electronic Control Unit (TECU) ignition voltage is greater than 7 volts and less than 16 volts.
  • FMI 10 requires the transmission to be in neutral and the vehicle speed must be within range.
  • FMI 2 does not set if there is already an Active FMI 5 for the Input or Output Shaft Speed Sensors.

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

Conditions to Set Fault Code Active

  • FMI 2 is set when the TECU input shaft speed is compared to the output shaft speed and it produces an inconsistent reading for 1 second or greater.
  • FMI 3 and 4 are set when the TECU detects a short to ground, short to battery, and the input shaft speed is 0 for 1 second or greater.
  • FMI 5 is set when the TECU detects an open circuit and the Input Shaft Speed Sensor is 0 for 1 second or greater.
  • FMI 10 is set when the TECU detects a 200 RPM or greater speed difference between the input shaft speed and the raw input shaft speed for 10 ms or greater.

Fallback When Fault Code 56 is set the following conditions occur:

  • Red “Service” light illuminates and an “F” flashes in the gear display.
  • Fault is stored in TECU memory.
  • The operation mode changes to “AutoShift Fallback” mode.
  • If this fault occurs while moving, the transmission remains in current gear and the clutch opens when the vehicle stops.
  • If this fault occurs at power up, the vehicle cranks but the transmission does not engage a gear.

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 2, 10
    • Input Shaft Speed Sensor
    • TECU
    • Transmission Harness
    • Damaged transmission gearing
    • Contamination on the Input Shaft Speed Sensor
  • FMI 3, 4, 5
    • Input Shaft Speed Sensor
    • TECU
    • Transmission Harness

Fault Code 56 – Input Shaft Speed Sensor Test

Component Identification:

Fuller Transmission Harness Front View TECU - Vehicle Interface Connector

Harness Front View
(TECU – System Interface Connector)

Fuller transmission Deutsch 4-way OEM connector

Input Shaft Speed Sensor
(Connect View)

NOTE: Refer to the Eaton Hybrid Component and Connector Location for Connector Locations in MY08 Systems

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

Eaton Fuller Transmission TECU Input Shaft Speed Sensor Connector Location

STEP 1. Verify continuity of Transmission Harness sensor circuits.

  1. Retrieve Active fault codes and FMIs with ServiceRanger using the 9-Way Diagnostic Connector.
  2. Key off.
  3. Disconnect negative battery cable.
  4. Disconnect the Transmission Harness 38- Way Connector.
  5. Measure the resistance between the Transmission Harness 38-Way Connector Pin 7 and Pin 8 and Pin 7 and ground.
    • If resistance is 2K–4.5K ohms and Pin 7 to ground is 10K ohms or greater, go to Step 2.
    • If resistance is outside of the range, go to Step 4.

STEP 2. Verify voltages of Transmission Harness sensor circuits and ground.

  1. Key on.
  2. Measure the voltage from between the Transmission Harness 38-Way Connector Pin 7 and ground.
    • If voltage is 0 volts, go to Step 3.
    • If voltage is 11–13 volts, repair the short to battery in the Vehicle Harness, then go to Step 6.

STEP 3. Verify integrity of Input Shaft Speed Sensor.

  1. Inspect Input Shaft Speed Sensor for contamination or damage:
    • If no problem found, replace Transmission Electronic Control Unit (TECU) (Only if Fault Code is Active), then go to Step 6.
    • If problem is found or were sent here from Step 4 or Step 5, replace Input Shaft Speed Sensor and inspect the Countershaft Gear for damage. Go to Step 6.

STEP 4. Verify continuity of Input Shaft Speed Sensor.

  1. Disconnect the Transmission Harness from Input Shaft Speed Sensor.
  2. Measure resistance between Input Shaft Speed Sensor Pin A and Pin B:
    • If resistance is 2K–4.5K ohms, go to Step 5.
    • If resistance is outside of range, go to Step 3.

STEP 5. Verify continuity of Input Shaft Speed Sensor to ground.

  1. Measure resistance between Input Shaft Speed Sensor Pin A and ground:
    • If resistance is 10K ohms or greater, replace the Transmission Harness, then go to Step 6.
    • If resistance is less than 10K ohms, go to Step 3.

STEP 6. Verify Repair.

  1. Key off.
  2. Reconnect all connectors and negative battery cable.
  3. Verify proper installation of speed sensor.
  4. Key on.
  5. Clear codes, see  Clear Inactive Faults.
  6. Drive the vehicle and attempt to reset the code.
  7. Check for codes, see View Active and Inactive Faults.
    • If no codes, test is complete.
    • If fault Code 56 appears, find error in testing, go to Step 1.
    • If a code other than 56 appears, see Fault Code Index List.

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