Case IH 3723 – ENGINE (EDC - Electronic Diesel Control unit): Lambda sensor: LSU sensor temperature Ri is below the minimum limit

This code indicates a failure in the heating circuit of the Lambda (Oxygen/O2) sensor. Specifically, the internal resistance (Ri) of the LSU sensor's heater is too low, meaning the sensor is failing to reach or maintain the minimum temperature required to accurately measure oxygen concentration in the exhaust gas.

• Farmall
• SR175
• SR250
• SV300
• Maxxum
• Optum
• Magnum
• Puma
• Skid Steers
• Compact Track Loaders

1. 1

   Inspect the wiring harness leading to the Lambda sensor for open circuits, chafing, or shorts

2. 2

   Disconnect the Lambda sensor and check the pins for corrosion, moisture, or pushed-out terminals

3. 3

   Measure the internal resistance of the Lambda sensor's heater circuit to verify if it has failed internally

4. 4

   Connect the Electronic Service Tool (EST) to monitor the Lambda sensor's live temperature and oxygen concentration data to confirm the sensor is unresponsive

1. 1

   Turn off the machine and disconnect the battery

   This prevents electrical spikes.

2. 2

   Locate the Lambda (O2) sensor

   Typically positioned upstream, before the catalytic converter/DPF in the exhaust system.

3. 3

   Repair wiring or connector

   If wiring damage is found during diagnostics, repair the harness or replace the damaged connector.

4. 4

   Remove the defective Lambda sensor

   If the wiring is intact, the sensor's internal heater has failed. Remove the defective Lambda sensor using an O2 sensor socket.

5. 5

   Install the new Lambda sensor

   Torque to OEM specifications and reconnect the wiring harness.

6. 6

   Reconnect the battery

7. 7

   Clear fault code and reset ECU data

   Connect the EST (Electronic Service Tool) to clear the 3723 fault code and perform a "Reset ECU data (Lambda sensor)" procedure so the engine control module calibrates to the new sensor.