Case IH 3720 – Engine Control Unit (ECU): 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' defect on the Lambda (Oxygen/O2) sensor circuit, indicating the voltage supplied to the sensor dropped below 9.0 Volts.

• Farmall
• Farmall 85A
• Farmall 95A
• Farmall 105A
• Farmall 115A
• Farmall 115U
• Puma 210
• SR175

1. 1

   Verify that the fault code is currently present and in an active state.

2. 2

   Inspect the electrical wiring and connectors between the Lambda sensor and the Engine ECU for corrosion, loose pins, or physical damage.

3. 3

   Measure the resistance of the sensor circuit while wiggling the harness to reveal any intermittent conditions.

4. 4

   If the resistance is less than 20,000 Ω, repair the short circuit to the chassis ground in the wiring harness.

5. 5

   If the resistance is greater than 20,000 Ω, temporarily connect a replacement Lambda sensor and retest to confirm an open circuit within the sensor.

6. 6

   Ensure the machine's battery and charging system are functioning properly and delivering adequate voltage (above 9.0V) to the engine electronics.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the battery ground cable to prevent damage to the electronic monitoring and charging systems.

2. 2

   Gain Access

   Locate the Lambda sensor on the exhaust system (typically near the EGR or DPF assembly). If necessary, loosen the system heat shield and remove the bonnet support to gain clear access to the left-hand side of the engine.

3. 3

   Remove the Sensor

   Disconnect the electrical connector for the Lambda sensor. Carefully unscrew the sensor from the exhaust pipe.

4. 4

   Install the New Sensor

   Thread the new Lambda sensor into the exhaust and tighten it to the manufacturer's specified torque.

5. 5

   Reassembly

   Reconnect the sensor's electrical harness. Reinstall any heat shields or supports that were removed. Reconnect the battery ground cable.

6. 6

   ECU Calibration

   Connect your electronic service tool (EST) to the machine, clear the inactive fault codes, and perform the 'Reset ECU data (Lambda sensor)' routine so the engine controller can calibrate to the new sensor.