New Holland ENG 3708 – Engine ECU: Lambda Sensor: Open circuit at the Lambda Sensor Pump Current Pin - IP (1 detection)

The Engine Control Unit has detected a break in the electrical circuit (an open circuit) specifically on the pump current wire of the wideband Lambda (Oxygen/O2) sensor, meaning the sensor cannot communicate oxygen concentration data back to the engine controller.

• T4
• T5
• T6
• T7
• Workmaster 60
• Workmaster 70
• L-Series
• C-Series
• L316
• L318
• L320
• SR175
• W50C
• W60C
• W70C
• W80C
• CR9090
• CX8080 Elevation
• CX8090 Elevation
• Farmall
• Puma
• Luxxum
• Optum

1. 1

   Visually inspect the Lambda sensor on the exhaust system, its 5-wire/6-pin connector, and the wiring harness for physical damage, melted wires, or corrosion

2. 2

   Disconnect the sensor and use a multimeter to check for continuity on the pump current pin wire between the sensor connector and the Engine ECU harness

3. 3

   Check the connector pins for terminal fretting or pushed-out pins that could cause a false open circuit

4. 4

   If the wiring harness and ECU connections test perfectly, suspect an internal failure of the Lambda sensor itself

1. 1

   Preparation

   Turn off the engine, remove the key, and disconnect the battery to prevent electrical spikes. Allow the exhaust system to cool completely.

2. 2

   Disconnect

   Unplug the electrical connector from the faulty Lambda sensor.

3. 3

   Removal

   Using a specialized O2 sensor socket (typically to fit an M18 x 1.5 thread), carefully unscrew the Lambda sensor from the exhaust pipe.

4. 4

   Harness Repair

   If your diagnostic checks revealed a broken wire in the machine's harness rather than a faulty sensor, splice and repair the wiring using OEM-approved weather-sealed connectors.

5. 5

   Installation

   If replacing the sensor, apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Thread the new sensor into the exhaust pipe by hand to prevent cross-threading, then tighten to the OEM torque specification.

6. 6

   Reconnect

   Plug the 5-wire/6-pin electrical connector back into the machine's harness, ensuring the locking tab clicks into place.

7. 7

   Clear Codes

   Reconnect the battery, turn the key on, and use the New Holland Electronic Service Tool (EST) to clear the ENG 3708 fault code. Start the engine and verify that the code does not return.