Case IH 3737 – Engine Control Unit (EDC / ECM): Lambda Sensor: Over temperature error of the LSU Heater Power stage

The internal heater circuit of the Lambda (Oxygen/O2) sensor is drawing too much current or overheating, which usually points to an internal short in the sensor's heater element or a short-to-battery in the wiring harness.

• skid steer
• Magnum series
• Maxxum series
• Puma series
• Steiger series
• Farmall series
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Inspect the Lambda sensor and its wiring harness for any signs of melting, chafing, or corrosion.

2. 2

   Check the wiring between the Lambda sensor and the EDC for a short circuit to the battery or an open circuit.

3. 3

   Test the heater circuit pins on the Lambda sensor itself to see if the internal resistance is out of specification (indicating an internal short causing the overheating power stage).

4. 4

   Ensure the pins at the Engine Control Unit (EDC) connector are clean and making good contact.

1. 1

   Turn off the machine and disconnect the battery

   Ensure safety while working with the engine harness.

2. 2

   Locate the Lambda (O2) sensor

   Typically located on the exhaust system upstream of the catalytic converter/DPF.

3. 3

   Disconnect the sensor's electrical connector

   Inspect for heat damage or pushed-out pins.

4. 4

   Remove the defective Lambda sensor

   If the wiring harness tests good but the sensor heater is internally shorted (causing the over-temperature fault), remove the defective Lambda sensor using an O2 sensor socket.

5. 5

   Install the new Lambda sensor

   Torque it to the manufacturer's specification.

6. 6

   Reconnect the sensor

   Reconnect the sensor to the engine wiring harness.

7. 7

   Reconnect the battery

8. 8

   Clear inactive fault codes

   Connect the Electronic Service Tool (EST) to the machine's diagnostic port and clear the inactive fault codes.

9. 9

   Run the engine and monitor the Lambda sensor data

   Monitor via the EST to ensure the heater power stage is operating at normal temperatures and the fault does not return. (Note: If the fault persists after replacing the sensor and verifying the wiring, OEM manuals note that the EDC may have suffered an internal failure and might need to be reprogrammed or replaced).