Eaton Fuller Hybrid Transmission Engine Crank Test
This symptom-driven test is performed if a “N” is displayed on the gear display with no Active or Inactive codes and the vehicle does not crank.
The Hybrid Control Module (HCM) receives the input to crank from Pin 20 on the HCM 38-Way Connector, which is wired to the Key Switch. The HCM normally powers the High-Voltage Motor/Generator to start the engine. If the hybrid system is offline, the HCM uses the standard 12-Volt Starter by energizing the 12-Volt Cranking Relay. This relay then provides battery power to Pin 30 of the Start Enable Relay, which then powers the Starter Solenoid.
Note: This symptom-based test should only be performed if directed here from the Diagnostic Procedure and there are no Active fault codes.
Eaton Fuller Hybrid Transmission Engine Crank Test Detection
The following symptoms may have been experienced:
- Vehicle does not crank or there is a solid “N” in the Gear Display.
Possible Causes
This fault code can be caused by any of the following:
- 12-Volt Cranking Relay
- Start Enable Relay
- Vehicle Harness
- Engine Starter
- 12-volt batteries
- Key Switch input to Pin 20 of the HCM
Eaton Fuller Hybrid Transmission Engine Crank Test Component Identification

Harness Front View
(TECU – Vehicle Interface Connector)

Harness Front View
(HCM – Hybrid System Interface Connector)
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.

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. Visually observe the Gear Display after power up.
- Perform this symptom test if only if directed to do so by the Symptom-Driven Diagnostic Index and there are no Active fault codes.
- Key on.
- Press N on the Push Button Shift Control:
Note: The ePTO light must be off when using the key switch to start the vehicle.- If “N” is present on the gear display, go to Step 2.
- If “N” is not present on the gear display, refer to the “Hybrid Diagnostic Procedure” for the correct symptom-based test to perform.
STEP 2. Verify Crank Request parameter.
- Key on.
- Connect ServiceRanger to the 9-Way Diagnostic Connector.
- Select the “Data Monitor” option and view the “Crank Request” parameter:
- If Crank Request reads 1 (Crank), go to Step 3.
- If Crank Request reads 0 (No Crank), go to Step 5.
STEP 3. Verify integrity of the Cranking Relay..
- Substitute a different start enable and 12-Volt Cranking Relay.
- Attempt to crank engine:
- If engine cranks, pinpoint which of the 2 relays was at fault and replace it. Go to Step 6.
- If engine does not crank, go to Step 4.
STEP 4. Verify power to the Start Enable Relay.
- Key on.
- Engine may crank.
- Jumper Pin 87 of the Start Enable Relay Connector to battery power:
- If engine cranks, repair open circuit between Pin 87 of the Start Enable Relay and battery. Refer to OEM for repair procedures.
- If engine does not crank, concern is with Starter Solenoid or Power Harness to Solenoid. Refer to OEM for repair procedures.
STEP 5. Verify voltage to ground on HCM Harness.
- Key off.
- Disconnect negative battery cable.
- Disconnect HCM Harness 38-Way Connector.
- Key in start position.
- Measure voltage from HCM Harness 38-Way Connector Pin 20 to ground.
- If voltage is 11–13 volts, replace the Hybrid Control Module (HCM), then go to Step 6.
- If voltage is below 11 volts, repair the Vehicle Harness, then go to Step 6.
STEP 6. Verify repair.
- Key off.
- Reconnect all connectors.
- Place Shift Control into neutral.
- Key on:
- If engine starts, test is complete.
- If engine does not start, find error in testing, go to Step 1.
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