Case IH 3855 – EDC (Electronic Diesel Control): Lambda sensor : Oxygen concentration implausibly low in part load operation

The lambda (oxygen) sensor is detecting an abnormally low amount of oxygen in the exhaust gases while the engine is operating under a partial load. This condition typically points to the engine running too rich (excessive fuel or insufficient air) or a failure of the sensor itself.

• Farmall 110A
• Farmall 120A
• Farmall 130A
• Farmall 140A
• Magnum 180-380
• Maxxum 115-150
• Puma 150-220
• Steiger 370-620
• Quadtrac 370-620

1. 1

   Check the lambda sensor's wiring harness and connectors for damage, corrosion, or short circuits (look for sub-code 3855-07).

2. 2

   Inspect the air intake for restrictions, such as a clogged air filter or issues with the EVGT (Electronic Variable Geometry Turbocharger), which could starve the engine of air.

3. 3

   Check for excessive fuel pressure, fuel inlet restrictions, or leaking electronically controlled injectors that could be dumping excess fuel.

4. 4

   Inspect the exhaust pipe for leaks upstream of the lambda sensor, which can skew the sensor's readings.

1. 1

   Connect a compatible OBDII scanner or CNH diagnostic tool to the machine to verify the active 3855 fault code.

   Verify the active 3855 fault code.

2. 2

   Perform the diagnostic checks listed above to rule out mechanical issues causing a rich fuel mixture (e.g., air starvation or leaking injectors).

   Rule out mechanical issues causing a rich fuel mixture.

3. 3

   Inspect the lambda sensor wiring. If the wiring is damaged, repair the harness.

   Repair the harness if wiring is damaged.

4. 4

   If the wiring and mechanical systems are functioning correctly, the lambda sensor itself is likely faulty and must be replaced.

   Replace the lambda sensor if other systems are functioning correctly.

5. 5

   Disconnect the negative battery terminal.

   Disconnect the negative battery terminal.

6. 6

   Locate the lambda sensor on the exhaust system, disconnect its 4-pin electrical connector, and use an oxygen sensor socket to carefully remove the old sensor.

   Remove the old lambda sensor.

7. 7

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied) and install it into the exhaust pipe, tightening to the OEM torque specification.

   Install the new sensor and tighten to OEM torque specification.

8. 8

   Reconnect the electrical connector and the battery.

   Reconnect the electrical connector and the battery.

9. 9

   Clear the fault codes from the EDC using the diagnostic tool.

   Clear the fault codes from the EDC.

10. 10

    Start the engine and test run the machine under part-load conditions to ensure the code does not return.

    Test run the machine under part-load conditions.