Eaton Fuller Hybrid Transmission Fault Code 40 – Cooling Pump 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.  Read below to learn how to test, clear and fix fault code errors for your Freightliner, Mack, Peterbilt, Kenworth, Volvo and International truck. The Cooling Pump Relay is 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 Cooling Pump Relay powers the Cooling Pump that circulates the coolant on the hybrid liquid system.

Fault Code 40 – Cooling Pump 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

  • FMI 3 is set when the HCM detects a short to battery in the coil circuit of the Cooling Pump Relay.
  • FMI 4 is set when the HCM detects a short to ground in the coil circuit of the Cooling Pump Relay.
  • FMI 5 is set when the HCM detects an open in the coil circuit of the Cooling Pump Relay.
  • FMI 14 is set when the following occur for 10 minutes or longer:
    • Inverter temperature is greater than 122 °F (50 °C)
    • The difference between the maximum battery temperature and the Inverter temperature is greater than 68 °F (20 °C)
    • No battery temperature or motor temperature faults

Fallback When Fault Code 40 is set the following conditions occur:

  • Amber “Check Hybrid” light illuminates.
  • Fault is stored in Hybrid Control Module (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 3, 4, 5
    • Vehicle Harness from HCM to Cooling Pump Relay
    • Cooling Pump Relay
    • HCM
  • FMI 14
    • Cooling Pump Relay
    • Cooling Pump
    • Cooling Pump Relay main power supply
    • Low coolant, Low coolant flow, plugged radiator, fan operation

Fault Code 40 – Cooling Pump Relay Test

Component Identification:

Harness Front View HCM - Hybrid System Interface Connector

Harness Front View
HCM – Hybrid System Interface Connector

Relay switch

Temperature Sensor
(Harness View – Front Side)

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 HCM Coolant Pump Connectors

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. Key off.
  4. 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.
  5. Exchange Cooling Pump Relay with another relay and see if fault returns:
    • If fault does not return with new relay, replace the Cooling Pump 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 from Step 1?
    Note: The cooling pump relay must be wired according to Eaton® requirements (shown on previous page) 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 32 and Pin 4.
    • If resistance between Pin 32 and Pin 4 is 40–120 ohms, replace Hybrid Control Module (HCM) (only if fault code is Active), then go to Step 9.
    • If resistance is outside of range, repair the Vehicle Harness for an open circuit, then go to Step 9.

STEP 4. Verify voltages of HCM Harness circuits to ground.

  1. Key on.
  2. Measure voltage between HCM Harness 38-Way Connector Pin 32 and ground at key on.
    • If voltage between Pin 32 and ground is 0 volts, replace the Hybrid Control Module (HCM) (only if fault code is Active), then go to Step 9.
    • If voltage between Pin 32 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 to ground.

  1. Key off.
  2. Disconnect negative battery cable.
  3. Disconnect the HCM System Harness 38- Way Connector.
  4. Measure the resistance between the HCM System Harness 38-Way Connector Pins 32 and ground:
    • If resistance between Pin 32 and ground is 10K ohms or greater, replace the Hybrid Control Module (HCM) (only if 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 level of Hybrid System coolant.

  1. Key off.
  2.  Note the level of the coolant in the Hybrid Liquid Cooling System:
    • If the coolant is within the recommended limits, go to Step 7.
    • If the coolant is below the recommended limits, refer to OEM for coolant type and fill procedure. Go to Step 9.

STEP 7. Verify operation of Hybrid System Coolant Pump.

  1. Key off.
  2. Connect ServiceRanger to the 9-Way Diagnostic Connector in the cab.
  3. Key on.
  4. Select the following options in ServiceRanger:
    “Advanced Product Functions,” “Hybrid Control Module,” and “Launch APF.”
  5. Go to “Product Tests” and select “Coolant Pump Relay.”
  6. Listen for the Coolant Pump to turn on and watch coolant flow in the reservoir.
    • If the Coolant Pump runs with coolant moving through the reservoir, and the Fault Code is Active, contact Eaton® at 1-800-826-4357.
    • If the Coolant Pump does not run, go to Step 8.
    • If the Coolant Pump runs and coolant does not flow, check for kinks or sharp bends in the coolant lines. If okay, contact OEM for concerns with Coolant Pump.

STEP 8. Verify voltages at Hybrid System Coolant Pump.

  1. Key on.
  2. Disconnect the 2-Way Connector at the Coolant Pump.
  3. Measure voltage at the 2-Way Connector from Pin A to Pin B.
    • If voltage between Pin A and Pin B is ±0.2 volts of battery voltage, refer to OEM for Coolant Pump problem.
    • If voltage between Pin A and Pin B 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 40 appears, find error in testing, go to Step 1.
    • If a code other than 40 appears, see Fault Code Index List.

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