Case IH 3713 – ENGINE ECU: Lambda sensor: Open Load error of the LSU Heater Power stage

The engine control system has detected an open circuit (a break in the electrical path) specifically on the heater power circuit of the Lambda sensor.

• skid steer
• Maxxum series (120, 135, 145, 150)
• Puma series (165)
• Farmall series (95U, 105U, 115U Pro EP)
• Steiger series
• Workmaster series
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• excavators

1. 1

   Inspect the wiring harness leading to the Lambda sensor in the exhaust system for melted wires, chafing, or physical damage caused by exhaust heat or debris.

2. 2

   Disconnect the Lambda sensor connector (5-wire/6-pin) and check for corrosion, pushed-back pins, or moisture inside the plug.

3. 3

   Turn the key to the ON position and use a multimeter to verify that battery voltage is reaching the heater power pin on the harness side of the connector.

4. 4

   Measure the resistance across the heater circuit pins on the sensor itself. If the multimeter reads infinite resistance (OL), the internal heater element is burnt out.

1. 1

   Preparation

   Ensure the machine is turned off, the battery is disconnected, and the exhaust system has completely cooled down to prevent burns.

2. 2

   Locate the Sensor

   Find the Lambda sensor mounted on the exhaust pipe, typically located upstream or downstream of the catalytic converter / DPF / SCR assembly.

3. 3

   Disconnect

   Unplug the electrical connector from the machine's wiring harness.

4. 4

   Removal

   Using a specialized O2 sensor socket (usually 22mm or 7/8") or a wrench, carefully unscrew the faulty Lambda sensor from the exhaust bung. If it is seized, apply penetrating oil and allow it to sit before attempting to loosen it.

5. 5

   Preparation of New Sensor

   Check the threads of the new sensor. If it does not come pre-greased, apply a small amount of high-temperature anti-seize compound to the threads (avoid getting any on the sensor tip).

6. 6

   Installation

   Thread the new sensor in by hand to prevent cross-threading, then tighten it to the manufacturer's specified torque.

7. 7

   Reconnect

   Plug the electrical connector back into the wiring harness, ensuring it clicks securely into place. Route the wire away from direct contact with the hot exhaust pipe.

8. 8

   Clear Codes

   Reconnect the battery, start the engine, and use the CNH Electronic Service Tool (EST) or a compatible OBD scanner to clear fault code 3713.