Case IH 3737 – Engine Control Unit (ECU) / EDC (Electronic Diesel Control): Lambda sensor: Over temperature error of the LSU Heater Power stage

This code indicates that the power stage (the electrical driver circuit) responsible for heating the Lambda (Oxygen) sensor is overheating. This is typically caused by excessive current draw resulting from a short circuit in the sensor's internal heater element, a short in the wiring harness, or an internal failure of the control module itself.

• Farmall
• Farmall series (115U Pro EP, 115C, 120C)
• Puma 210
• Steiger / Magnum series
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Visually inspect the wiring harness and connectors running from the EDC to the Lambda sensor for chafed wires, melted insulation, or moisture that could cause a short.

2. 2

   Disconnect the Lambda sensor and use a multimeter to check the resistance of the internal heater circuit pins (a dead short near zero ohms indicates a failed sensor).

3. 3

   Verify the machine's battery and alternator charging voltage, as abnormally high or low voltage can affect power stage diagnostics.

4. 4

   Check for accompanying EDC internal faults (such as 3738) or other Lambda sensor circuit codes (3707–3713, 3724, 3725) to help pinpoint if the short is at the sensor or internal to the ECU.

1. 1

   Disconnect Power

   Always disconnect the negative battery cable before servicing engine management sensors or the EDC.

2. 2

   Repair Wiring

   If the diagnostic checks revealed a short in the harness, repair the damaged wiring or replace the harness section.

3. 3

   Replace the Lambda Sensor

   If the sensor's heater element is shorted, unthread the old Lambda sensor from the exhaust/DPF assembly. Apply a small amount of anti-seize to the threads of the new sensor (many OEM sensors come pre-greased) and torque it to the manufacturer's specification. Reconnect the 5-pin harness.

4. 4

   EDC Replacement

   If the wiring and sensor are perfectly intact, the power stage driver inside the EDC has likely suffered an irreversible internal failure. The Engine Controller must be reprogrammed or replaced. If the EDC is replaced, you must use the CNH Electronic Service Tool (EST) to restore self-learning parameters.

5. 5

   Clear Codes and Test

   Reconnect the battery, clear the fault codes using a diagnostic tool, and run the engine under load to verify the code does not return.