New Holland ENG 3737 – Engine ECU: Lambda Sensor: Over temperature error of the LSU Heater Power stage.

The Engine Control Unit (ECU) has detected an over-temperature condition either within the sensor's internal heater circuit or at the ECU's internal power stage that drives the heater. This can be caused by a short circuit, a failing sensor heater element, or extreme exhaust temperatures.

• T5 series
• T6 series
• T7 series
• T8 series
• T9 series
• Workmaster 60
• Workmaster 70
• CR series
• CR9090
• CX series
• CX8080 Elevation
• CX8090 Elevation
• L-Series
• C-Series

1. 1

   Inspect the wiring harness running from the Engine ECU to the Lambda sensor for melted insulation, chafing against the frame, or pinched wires that could cause a short circuit.

2. 2

   Disconnect the Lambda sensor and inspect the 5-wire/6-pin connector for melted pins, corrosion, or moisture intrusion which can cause resistance issues.

3. 3

   Using a multimeter, measure the resistance of the heater circuit pins on the sensor side. An out-of-spec or open reading indicates the sensor's internal heater has failed.

4. 4

   Turn the key to the ON position and verify that the harness side of the connector is receiving proper battery voltage and ground from the ECU.

5. 5

   Ensure the machine is not suffering from a separate issue causing abnormally high Exhaust Gas Temperatures (EGTs), such as a clogged DPF or over-fueling, which could physically overheat the sensor.

1. 1

   Preparation

   Park the machine on a level surface, turn off the engine, remove the key, and disconnect the negative battery cable. Allow the exhaust system to cool completely to prevent severe burns.

2. 2

   Locate the Sensor

   Locate the Lambda sensor on the exhaust system. It is typically threaded into the exhaust pipe near the Oxidation Catalyst or Diesel Particulate Filter (DPF) assembly.

3. 3

   Disconnect Wiring

   Unplug the sensor's electrical connector. Unclip the wire from any retaining brackets.

4. 4

   Remove the Sensor

   Using a 22mm (7/8") specialized O2 sensor socket or a wrench, carefully unscrew the Lambda sensor from the exhaust bung.

5. 5

   Clean the Threads

   Inspect the threads in the exhaust pipe. Use a thread chaser to clean out any carbon buildup or galling if necessary.

6. 6

   Prepare the New Sensor

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

7. 7

   Install the New Sensor

   Thread the new sensor in by hand to ensure it does not cross-thread. Tighten it to the OEM specified torque (usually around 30-40 Nm).

8. 8

   Reconnect

   Plug the electrical connector back in until it clicks. Ensure the wiring is routed safely away from hot exhaust components and moving parts.

9. 9

   Clear Codes

   Reconnect the battery. Connect a diagnostic tool (like the CNH Electronic Service Tool) to clear the ENG 3737 fault code. Start the engine and monitor the sensor data to verify the heater circuit is operating normally.