Case IH 3721 – Engine ECU / Planter UCM: Lambda Sensor SPI Chip Error / Row Lift Proximity Switch Failure

Indicates an internal hardware or communication failure (SPI chip error) within the Lambda (Oxygen) sensor circuit on tractors/loaders, or a proximity switch device failure (above-normal voltage or short to power) on the Row Lift Proximity Switch on planters.

• skid steer
• Case IH Farmall 85A
• Case IH Farmall 95A
• Case IH Farmall 105A
• Case IH Farmall 115A
• Case IH Farmall 80N
• Case IH Farmall 80V
• TR270 compact track loaders
• 580SN backhoe loaders
• Case IH 2140 Early Riser
• Case IH 2150S Early Riser
• Case IH 2160 Early Riser

1. 1

   For Engine Lambda Sensor (Tractors/Loaders): Inspect the wiring harness and 5-wire connector between the Lambda sensor and the Engine ECU for melted wires, chafing, or corrosion.

2. 2

   For Engine Lambda Sensor (Tractors/Loaders): Verify that the sensor is receiving proper battery voltage, as low voltage at the SPI chip can trigger similar faults.

3. 3

   For Engine Lambda Sensor (Tractors/Loaders): If wiring and voltage supply are intact, the SPI chip error indicates an internal failure of the sensor circuitry itself.

4. 4

   For Planter Proximity Switch (Planters): Check the harness connection to the row lift proximity sensor for a short to power.

5. 5

   For Planter Proximity Switch (Planters): Verify the sensor is not physically damaged or packed with field debris.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the battery to ensure safety and prevent electrical spikes. Allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the Lambda sensor on the exhaust system. It is typically positioned upstream (before) the catalytic converter or DPF.

3. 3

   Clear Access

   If necessary, loosen or remove the exhaust heat shield and bonnet supports to gain clear access to the sensor.

4. 4

   Disconnect

   Unplug the electrical connector linking the Lambda sensor to the engine wiring harness.

5. 5

   Removal

   Using an O2 sensor socket or wrench, carefully unscrew the faulty Lambda sensor from the exhaust pipe.

6. 6

   Installation

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied). Thread the new sensor into the exhaust pipe and tighten to the manufacturer's torque specification.

7. 7

   Reassembly

   Reconnect the electrical connector and reinstall any heat shields that were removed.

8. 8

   Clear Codes

   Reconnect the battery. Use the Case IH Electronic Service Tool (EST) or a compatible diagnostic scanner to clear the fault code from the Engine ECU.

9. 9

   Test

   Start the engine and verify that the fault code does not return.