New Holland 3145 – ECU: Terminal 15 - No Signal

The Engine Control Module (ECM) is not detecting the 'key on' power signal from Terminal 15. This circuit provides a switched 12-volt positive signal when the ignition is in the 'ON' or 'RUN' position to wake up the ECM. The loss of this signal prevents the ECM from powering up, which can result in a no-start condition or intermittent engine shutdowns. This missing signal may also affect the operation of other components or systems that rely on it.

• T8.275
• T8.300
• T8.320
• T8.330
• T8.360
• T8.390
• T8.420

1. 1

   Verify battery voltage is fully charged (above 12.4V) and ensure all battery terminals and main ground connections to the chassis and engine are clean, tight, and free of corrosion.

2. 2

   Visually inspect the wiring harness between the ignition switch, main fuse/relay box, and ECU for chafing, rodent damage, or corrosion. Pay close attention to the harness that runs down the front of the cab behind the engine, as this is a known area for potential rubbing.

3. 3

   Locate and test the ignition fuses (e.g., 10-amp fuse for battery power to key switch) for continuity.

4. 4

   Inspect the Main/ECU Power Relay by swapping it with an identical, known-good relay from a non-critical circuit (e.g., horn or work lights).

1. 1

   Test the ignition switch

   Access the back of the ignition switch connector. With the key OFF, identify the constant +12V wire (Terminal 30). Turn the key ON and probe for +12V on the Terminal 15 output wire. Replace the switch if there is no +12V output.

2. 2

   Test the ECU power relay circuit

   Remove the ECU power relay. With the key ON, test the socket for constant +12V, switched +12V trigger from the ignition, and ground. If the switched +12V is missing, repair the open circuit between the switch and relay. If inputs are correct, test the relay independently by applying 12V and ground to its control circuit (trigger) terminals and checking for continuity across its switched terminals.

3. 3

   Test for voltage at the ECU

   Safely back-probe the Terminal 15 input pin at the main ECU connector with the key ON. If +12V is missing but was present at the relay output, repair the open circuit in the harness. If +12V is present, suspect a rare internal ECU fault.