New Holland ENG 3720 – Engine Control Unit (ECU / EDC): Lambda Sensor: Low Battery Voltage at the SPI chip

The Serial Peripheral Interface (SPI) chip within the control module has detected a 'very low battery voltage' condition related to the Lambda (Oxygen) sensor circuit. Specifically, the voltage has dropped below the minimum threshold of 9.0 V, preventing the sensor from operating correctly and accurately measuring exhaust gases.

• T4.90
• T4.100
• T4.110
• T4.120
• T5.90
• T5.95
• T5.100
• T5.110
• T5.120
• T6 series
• T7 series
• Boomer series
• Workmaster series
• Speedrower 130
• Speedrower 160
• Speedrower 200
• Speedrower 220
• Speedrower 240
• Speedrower 260
• TH series telehandlers
• LM series telehandlers
• B-series backhoes
• L/C-series skid steers

1. 1

   Verify that fault code ENG 3720 is currently active and not just a stored historical code.

2. 2

   Test the main battery voltage and the alternator charging output to ensure the system is maintaining proper voltage (well above the 9.0 V failure threshold).

3. 3

   Thoroughly inspect the electrical wiring harness and connectors leading to the Lambda sensor for chafed wires, corrosion, or loose pins that could cause a voltage drop.

4. 4

   Verify that the Engine ECU is sending the correct reference voltage to the sensor. If the wiring is good but the voltage is low at the source, the ECU itself may be faulty.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery terminal to prevent electrical shorts.

2. 2

   Locate the Sensor

   Find the Lambda (Oxygen) sensor, which is mounted on the exhaust system / DPF assembly.

3. 3

   Disconnect the Harness

   Unplug the 5-wire or 6-pin electrical connector from the Lambda sensor.

4. 4

   Repair Wiring (If Applicable)

   If the diagnostic checks revealed damaged wiring or a corroded connector, repair the harness or replace the pigtail connector.

5. 5

   Remove the Sensor

   If the wiring is intact and the sensor is deemed faulty, use an O2 sensor socket or wrench to carefully unthread the Lambda sensor from the exhaust pipe.

6. 6

   Install the New Sensor

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied) and thread it into the exhaust. Tighten to the manufacturer's specified torque.

7. 7

   Reconnect

   Plug the electrical connector back in, ensuring it clicks and locks securely. Reconnect the negative battery terminal.

8. 8

   Clear Codes

   Connect a diagnostic tool to the machine, clear the ENG 3720 fault code, and run the engine to verify the repair.