Case IH 3711 – Engine Control Unit (ECU) / EDC (Electronic Diesel Control): Lambda sensor: SCB error of the LSU Heater Power stage

The engine control module has detected a short to battery voltage (SCB) in the internal heater circuit of the Lambda (Oxygen/O2) sensor. This prevents the heater from functioning correctly, which compromises emissions control and fuel trim adjustments.

• Farmall
• Farmall 115U Pro EP
• Magnum series
• Puma series
• SR175

1. 1

   Inspect the wiring harness leading from the Engine ECU to the Lambda sensor for melted insulation, chafing, or pinched wires that could cause a short to a 12V power source.

2. 2

   Disconnect the Lambda sensor and check both sides of the connector for water intrusion, corrosion, or damaged/pushed-out pins.

3. 3

   With the sensor disconnected and the key ON, use a multimeter to check the heater circuit pins on the harness side for unintended battery voltage.

4. 4

   Measure the resistance across the heater pins on the sensor itself to determine if the sensor has failed internally (out of specification or dead short).

1. 1

   Preparation

   Turn off the engine, remove the key, and disconnect the battery ground cable to prevent electrical damage. Allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the Lambda sensor, which is threaded into the exhaust pipe (typically upstream of the catalytic converter or DPF unit).

3. 3

   Removal

   Disconnect the sensor's electrical connector. Use a specialized 22mm (7/8") O2 sensor socket to carefully unthread the sensor from the exhaust pipe.

4. 4

   Preparation of New Sensor

   If the new sensor does not come with anti-seize compound pre-applied to the threads, apply a small amount of high-temperature, sensor-safe anti-seize. Note: Do not get any compound on the sensor tip.

5. 5

   Installation

   Thread the new Lambda sensor into the exhaust by hand to prevent cross-threading, then tighten it to the OEM torque specification using the sensor socket.

6. 6

   Reconnection

   Route the wiring harness away from extreme heat sources and reconnect the electrical plug.

7. 7

   System Reset

   Reconnect the battery. Connect a diagnostic tool (such as the CNH Electronic Service Tool) to clear the fault codes. Run the 'Reset ECU data (Lambda sensor)' routine so the ECU can calibrate to the new sensor.