New Holland 3713 – Engine ECU: Lambda Sensor Heater Open Circuit

The Engine Control Unit (ECU) has detected an open circuit in the electrical circuit responsible for powering the heater element of the Lambda (Oxygen) Sensor. The heater is essential for bringing the sensor to its optimal operating temperature quickly to ensure accurate measurement of oxygen in the exhaust gases. An open load error indicates the ECU is not detecting the expected electrical load, suggesting a break in the wiring, a faulty connection, or a failed heater element within the sensor itself.

• T4
• T5
• WORKMASTER
• B110C
• B110CTC
• C238
• TR340
• TV380
• BOOMER
• 580 ST
• 590 ST
• FARMALL
• T5.100

1. 1

   Visually inspect the wiring harness and connectors between the Lambda sensor and the engine ECU for chafing, corrosion, loose pins, or contact with hot exhaust components.

2. 2

   With the ignition on and engine off, verify that battery voltage (12-14V) is being supplied to the heater circuit at the sensor's electrical connector.

3. 3

   Disconnect the Lambda sensor and measure resistance across the two heater pins (typically the two wires of the same color). Expected resistance is 2-20 Ohms when cold; infinite resistance indicates a failed sensor.

4. 4

   Check the continuity of the wiring harness between the sensor connector and the ECU (specifically the low-side driver wire) to rule out an open circuit in the vehicle harness.

1. 1

   Isolate the fault

   Perform diagnostic checks to confirm whether the open circuit is located within the Lambda sensor's internal heater or the vehicle's wiring harness.

2. 2

   Replace or repair faulty component

   If the sensor's internal heater has infinite resistance, replace the Lambda sensor. If the wiring lacks continuity, repair or replace the damaged section of the harness.

3. 3

   Reset ECU data

   If the Lambda sensor was replaced, use the New Holland Electronic Service Tool (EST) to perform the 'Replacement of the Lambda Sensor - Reset ECU Data' procedure. This clears learned values for the new component.

4. 4

   Clear fault codes

   Use the EST or the vehicle's dashboard procedure to clear all active and stored fault codes.

5. 5

   Verify the repair

   Start the engine, allow it to reach operating temperature, and use the EST to monitor the Lambda sensor and heater circuit parameters to confirm the fault is resolved.