New Holland ENG 3725 – Engine ECU: Lambda sensor: Short to ground at IA, IP, UN, VG.

The Engine Control Unit (ECU) has detected a low voltage source on the Lambda (Oxygen) sensor circuit. Specifically, the internal SPI chip reports a "very low battery voltage" defect, meaning the voltage on the sensor circuit has dropped below 9.0 V, indicating a short to ground on one of the sensor's pins (IA, IP, UN, or VG).

• Boomer T4 PowerStar
• T5
• T5.95
• T6
• T7
• T8
• T9
• CR9090
• CX8080 Elevation
• CX8090 Elevation
• W50C ZB
• W60C ZB
• W70C HS
• W70C
• W80C HS
• W80C
• L-Series
• C-Series

1. 1

   Verify if the fault code is currently active or stored in history. If inactive, clear the code and operate the machine to see if it returns.

2. 2

   Inspect the wiring harness and connectors running from the Engine ECU to the Lambda sensor for signs of corrosion, abrasion, melted wires, or incorrect attachment.

3. 3

   Measure the sensor supply voltage at the Lambda sensor connector with the key ON (the system flags a voltage drop below 9.0 V).

4. 4

   Disconnect the ECU and the Lambda sensor, then measure continuity on the signal and ground wires (IA, IP, UN, VG pins) to chassis ground to confirm if there is a short in the harness.

1. 1

   Repair Wiring

   If the multimeter tests reveal a short to ground in the harness between the sensor and the ECU, locate the chafed or melted section of the wire and repair/replace the damaged wiring harness.

2. 2

   Replace the Lambda Sensor

   If the wiring harness tests perfectly (no shorts to ground and proper continuity), the internal circuitry of the Lambda sensor has likely failed and shorted out. Remove the old sensor from the exhaust system and install a new OEM Lambda sensor.

3. 3

   ECU Verification

   If both the wiring and the new sensor do not clear the active fault, the Engine ECU's internal power stage (SPI chip) may be damaged. Re-flash the ECU software first. If the fault persists after a re-flash, the ECU must be replaced.

4. 4

   Clear Codes

   After repairs, use a diagnostic tool to clear the ENG 3725 code and run the engine to verify the repair.