New Holland 3722 – ECM: Lambda Sensor: LSU Sensor Temperature Ri Exceeds Maximum Limit

The engine utilizes a Bosch LSU-style wideband Lambda (Oxygen / O2) sensor to measure the oxygen content in the exhaust gas. This sensor relies on an internal heater to reach operating temperature, and the engine computer monitors this temperature by measuring the sensor's internal resistance (Ri). Fault code ENG 3722 is triggered when the internal temperature measurement (Ri) exceeds the maximum allowable limit programmed into the software. This typically indicates that the sensor is overheating due to a failed internal heater control, a degraded sensor element, or abnormally high exhaust gas temperatures.

• T4.75
• T4.85
• T4.95
• T4.105
• T4.115
• T5.95
• T5.105
• T5.115
• L221
• L223
• L225
• L228
• L230
• C227
• C232
• C238
• B95C
• B95CLR
• B95CTC
• B110C
• W50C
• W60C
• W70C
• W80C
• 121F
• 221F
• 321F
• U80C
• 570N EP Loader Landscapers

1. 1

   Visually inspect the Lambda sensor's wiring harness and connector for melted or frayed wires, corrosion, or loose connections.

2. 2

   Check for related fault codes (e.g., 3711, 3724, 3725) that may indicate heater circuit or other wiring faults.

3. 3

   Verify the power supply to the sensor's heater circuit is receiving the correct voltage (10.5 to 13.5 V) when activated by the ECM.

4. 4

   With the engine off, disconnect the sensor and measure the resistance of the heater circuit (typically across the two white wires).

5. 5

   With the engine running at operating temperature, measure the sensor's signal wire voltage. A functioning zirconia-type sensor should fluctuate between 0.1 and 0.9 volts; a static reading or no voltage indicates a faulty sensor.

1. 1

   Prepare machine for service

   Park on a level surface, engage the parking brake, lower all attachments, turn off the engine, remove the key, and switch off the battery disconnect if available.

2. 2

   Locate the Lambda sensor

   Find the sensor in the exhaust system, typically located in the exhaust manifold or downstream from the Diesel Oxidation Catalyst (DOC).

3. 3

   Remove the faulty sensor

   Disconnect the electrical connector. Use an oxygen sensor socket or wrench to remove the old sensor. Apply penetrating oil if the sensor is seized.

4. 4

   Install the new sensor

   Clean carbon deposits from the exhaust pipe. Apply a small amount of anti-seize compound to the threads (avoiding the sensor tip). Thread the new sensor in by hand to prevent cross-threading, tighten to the manufacturer's specified torque, and reconnect the harness.

5. 5

   Clear codes and verify repair

   Use a diagnostic tool to clear fault code 3722 from the ECM. Start the engine, run it to operating temperature, and monitor the Lambda sensor's temperature to ensure it operates within the correct range without the code returning.