Eaton Fuller Hybrid Transmission Fault Code 38 – Battery Fan Relay

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 Battery Fan Relay is normally an open relay connected to the Hybrid Control Module (HCM) on the control side. When the HCM powers the control circuit, it closes the relay contacts and turns on the relay. The Battery Fan Relay powers the Battery Fan located in the Power Electronics Carrier (PEC), cooling the high-voltage batteries.

Fault Code 38 – Battery Fan Relay 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.

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

Conditions to Set Fault Code Active

Conditions to Set Fault:
• FMI 3 is set when the sensor voltage is greater than 4.1 volts for 10 seconds, while the Inverter temperature is over 35 °C or 95 °F, or if the sensor output voltage is less than 0.2 volts for 10 seconds.

Fallback When Fault Code 38 is set the following conditions occur:

  • FMI 3 is set when the HCM detects a short to battery in the coil circuit of the Battery Fan Relay.
  • FMI 4 is set when the HCM detects a short to ground in the coil circuit of the Battery Fan Relay.
  • FMI 5 is set when the HCM detects an open in the coil circuit of the Battery Fan Relay.
  • FMI 14 is set when the following conditions are true for 10 minutes:
    • High-voltage battery temperature is greater than 131 °F (55 °C)
    • Difference between the minimum and maximum battery temperatures is less than 33 °F (1 °C)
    • No battery temperature faults from the Battery Control Module

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 3, 4, 5
    • Vehicle harness from HCM to Battery Fan Relay
    • Battery Fan Relay
    • HCM
  • FMI 14
    • Battery Fan Relay
    • Battery Fan
    • Plugged Air Filter
    • Battery Fan Relay main power supply

Fault Code 38 – Battery Fan Relay Test

Component Identification:

Front Harness View HCM - Hybrid System Interface Connector

Front Harness View
HCM – Hybrid System Interface Connecto

Harness Connector View (PEC 19 - Way)

Harness Connector View
(PEC 19 – Way)

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 HCM Battery Fan Relay PEC Battery connector
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

High-Voltage Service Shutdown and Power-Up Procedure1. 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 Locations MY08 Systems

Eaton Hybrid Component and Connector Location MY09 Systems

Eaton Hybrid Component and Connector Locations MY09 Systems

STEP 1. Check for Active or Inactive fault code status.

  1. Review and follow the Warnings & Cautions.
  2. Retrieve Active fault codes and FMIs with ServiceRanger using the 9-Way Diagnostic Connector.
  3. Disconnect the Temperature Sensor Connector at the Motor/Generator.
    Danger: See High-Voltage Service Shutdown and Power-Up Procedures. Follow the procedures to avoid shock, burn or death from improperly handled high-voltage. Follow the procedures to avoid shock, burn or death from improperly handled high-voltage.
  4. Exchange Battery Fan Relay with another relay to see if fault returns.
    • If fault does not return with new relay, replace the Battery Fan Relay, then go to Step 9.
    • If fault returns with new relay, go to Step 2.

STEP 2. Verify FMI present.

  1. Which FMIs were listed in Step 1?
    Note* The battery fan must be wired according to Eaton® requirements for this test to work properly. If wired differently, consult OEM for correct wiring schematic.

    • If FMI 5 is listed, go to Step 3.
    • If FMI 3 is listed, go to Step 4.
    • If FMI 4 is listed, go to Step 5.
    • If FMI 14 is listed, go to Step 6.

STEP 3. Verify continuity of HCM Harness circuits.

  1. Key off.
  2. Disconnect negative battery cable.
  3. Disconnect the HCM Harness 38-Way Connector.
  4. Measure the resistance between the HCM Harness 38- Way Connector Pin 26 and Pin 4
    • If the resistance between Pin 26 and Pin 4 is 40–120 ohms, replace Hybrid Control Module (HCM) (Only if Fault Code is Active), then go to Step 9.
    • If the resistance is outside the range, repair the Vehicle Harness for an open circuit, then go to Step 9.

STEP 4. Verify voltages of HCM Harness circuits.

  1. Key on.
  2. Measure voltage between HCM Harness 38-Way Connector Pin 26 and ground at key on:
    • If voltage between Pin 26 and ground is 0 volts, replace the Hybrid Control Module (HCM) (only is fault code is Active), then go to Step 9.
    • If voltage between Pin 26 and ground is 12 volts, repair the short to VBATT on the Harness, then go to Step 9.

STEP 5. Verify continuity of HCM Harness circuits.

  1. Key off.
  2. Disconnect negative battery cable.
  3. Measure the resistance between HCM System Harness 38-Way Connector Pins 26 and ground:
    • If resistance between Pin 26 and ground is 10K ohms or greater, replace the Hybrid Control Module (HCM) (only is fault code is Active), then go to Step 9.
    • If resistance is outside of range, repair the Vehicle Harness for a short to ground, then go to Step 9.

STEP 6. Verify condition of PEC Air Filter Element.

  1. Key off.
  2. Remove and inspect the Air Filter on the PEC Inlet and the Exhaust Screen on the PEC Outlet.
    • If the Air Filter and Exhaust Screen are clean and free from debris, go to Step 7.
    • If the Air Filter is dirty or the Exhaust Screen is plugged, replace the Air Filter and clean the Exhaust Screen. Go to Step 9.

STEP 7.Verify operation of PEC Battery Fan.

  1. Key off.
  2. Connect ServiceRanger to the 9-Way Diagnostic Connector in the cab.
  3. Key on.
  4. Select the following options from ServiceRanger menus: “Advanced Product Function,” “Hybrid Control Module,” and “Launch APF.”
  5. Go to Product Tests and select Battery Fan Relay.
  6. Check for airflow from the front and rear air ports in the PEC.
    • If airflow can be felt from the PEC air inlet and exhaust, If Fault Code is Active contact Eaton® at 1-800-826-4357.
    • If airflow can not be felt from the PEC Air Inlet and Exhaust, go to Step 8.

STEP 8. Verify voltages of PEC Harness circuits.

  1. Key on.
  2. Disconnect the 19-Way Connector at the PEC.
  3. Measure voltage at the 19-Way Connector from Pin 12 to Pin 14:
    • If voltage between Pin 12 and Pin 14 is ±0.2 volts of battery voltage, replace the Power Electronics Carrier (PEC), then go to Step 9.
    • If voltage between Pin 12 and Pin 14 is outside of range, repair wiring or relay problem. Refer to OEM.

STEP 9. 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 38 appears, find error in testing, go to Step 1.
    • If a code other than 38 appears, see Fault Code Index List.

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