Case IH 3724 – ENGINE: Lambda Sensor: Short to Battery at IA, IP, UN, VG

The engine control system has detected that the voltage in the lambda (oxygen) sensor circuit is too high, indicating a short circuit to the battery positive (+) on one or more of the sensor's circuits (IA, IP, UN, or VG pins). When this occurs, the system may reduce engine torque to protect the engine.

• skid steer
• Skid Steer Loaders (SSL)
• SR175
• Compact Track Loaders (CTL)
• Farmall 115U Pro EP
• Puma 210
• Steiger
• Maxxum
• F5C
• F5H

1. 1

   Inspect the lambda sensor, its electrical connector, and the wiring harness routing back to the Engine ECU for chafing, melted insulation, or pinched wires that could cause a short to battery power.

2. 2

   Disconnect the lambda sensor connector and use a multimeter to check the harness-side pins (IA, IP, UN, VG) for voltage with the key on. If battery voltage is present, the wiring harness is shorted.

3. 3

   Check the internal resistance of the lambda sensor element across its pins. Out of specification values or continuity between the heater and signal circuits indicate an internal short.

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical spikes during repair.

2. 2

   Harness Repair

   If the diagnostic tests revealed a short in the wiring harness, locate the damaged section of the wire. Splice and repair the wire using weather-resistant heat-shrink connectors, or replace the affected harness section.

3. 3

   Sensor Replacement

   If the wiring is intact and the short is internal to the sensor: Disconnect the lambda sensor electrical connector. Use an oxygen sensor socket (typically 22mm) to carefully unthread the faulty lambda sensor from the exhaust/DPF system. Apply a small amount of high-temp anti-seize to the threads of the new sensor, thread the new sensor into the exhaust and tighten to the manufacturer's torque specification. Reconnect the electrical connector and secure the wiring away from extreme heat sources.

4. 4

   Clear Codes

   Reconnect the battery. Connect the Case IH Electronic Service Tool (EST), clear the inactive 3724 fault code, and run the engine to verify the code does not return.