Case IH 3725 – Engine Control Unit (ECU): Lambda sensor: short to ground at IA, IP, UN, VG.

The Engine Control Unit's SPI chip has reported a "very low battery voltage" defect (voltage dropping below 9.0 V) on the Lambda (Oxygen) sensor circuit. This indicates a low voltage source has been detected, typically caused by a short circuit to ground on the sensor's specific pins (IA, IP, UN, VG).

• Farmall
• Farmall 115U Pro EP
• Farmall 100C
• Steiger
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Visually inspect all connectors, pins, and the wiring harness leading to the Lambda sensor for broken connectors, corrosion, bent pins, or wire breaks.

2. 2

   Disconnect the engine harness from the ECU, turn the ignition ON, and test the wiring harness pins (e.g., X-014 pins 1, 2, 5, and 6) to ground using a multi-meter to ensure no voltage is present.

3. 3

   Turn the ignition OFF and use a multi-meter to check for solid continuity on the engine harness between the ECU connector and the Lambda sensor connector.

1. 1

   Repair Wiring

   If any of the voltage or continuity tests fail, or if visual damage is found, locate and repair the damaged wiring harness or replace the faulty connector pins.

2. 2

   Replace Sensor

   If the wiring harness passes all continuity and voltage tests, the internal circuitry of the Lambda sensor has failed. Replace the oxygen/Lambda sensor.

3. 3

   Reset ECU Values

   After installing the new sensor, you must connect the Case IH Electronic Service Tool (EST) to the machine's diagnostic port. Use the EST to reset the ECU oxygen sensor learning values and clear the fault code.