Case IH 3708 – Engine Control Module (ECM / ECU): Lambda Sensor: Open circuit at the Lambda Sensor Pump Current Pin - IP (1 detection)

The engine's computer has detected a break in the electrical circuit (an open circuit) specifically on the pump current pin of the exhaust Lambda (Oxygen/O2) sensor.

• skid steer
• Farmall 60A
• Farmall 70A
• Farmall 85A
• Farmall 105C
• Farmall 115U Pro EP
• SR series
• SV series
• TR series
• TV series
• Workmaster 50
• Workmaster 60
• Workmaster 70
• T4 series
• T5 series

1. 1

   Visually inspect the Lambda sensor wiring harness for melting, chafing, or rodent damage.

2. 2

   Disconnect the 5-wire connector to the Lambda sensor and check the pins for corrosion, moisture, or pushed-out terminals.

3. 3

   Perform a continuity test between the sensor connector and the ECM harness to rule out a broken wire in the machine's main harness.

4. 4

   Measure the internal resistance of the Lambda sensor's heater and pump circuits. If it reads as an open circuit internally, the sensor has failed.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the negative battery cable. Ensure the exhaust system has completely cooled down to prevent burns.

2. 2

   Access

   Depending on the model, you may need to remove the hood, side panels, or exhaust heat shields to access the DPF/exhaust pipe area.

3. 3

   Removal

   Disconnect the 5-pin electrical connector from the Lambda sensor. Using a specialized O2 sensor socket or a 22mm wrench, carefully unscrew the sensor from the exhaust pipe.

4. 4

   Preparation of New Sensor

   Check the threads of the new Lambda sensor. If it does not come with anti-seize pre-applied, apply a small amount of high-temperature oxygen-sensor-safe anti-seize to the threads. Caution: Do not get any anti-seize on the sensor tip, as this will ruin the sensor.

5. 5

   Installation

   Thread the new sensor into the exhaust pipe by hand to prevent cross-threading, then tighten it to the OEM torque specification (usually around 35-45 Nm).

6. 6

   Reassembly

   Reconnect the 5-pin electrical connector and secure the wiring harness away from extreme heat sources. Reinstall any heat shields or panels removed during access.

7. 7

   Calibration/Reset

   Reconnect the battery. Connect the CNH Electronic Service Tool (EST) diagnostic laptop to the machine. Clear the inactive 3708 fault code and perform the "Reset ECU data (Lambda sensor)" routine so the ECM learns the new sensor's resistance values.