Case IH 3408 – Engine ECU: Lambda sensor: Oxygen concentration implausibly high

This code indicates that the engine's Lambda (Oxygen) sensor is reading an oxygen level in the exhaust gas that is higher than physically plausible for the engine's current operating conditions.

• Farmall
• Maxxum
• Puma
• Magnum

1. 1

   Inspect for exhaust leaks upstream of the Lambda sensor, which can draw fresh air into the exhaust stream and cause a false reading.

2. 2

   Check the 5-wire wiring harness and connectors going to the Lambda sensor for chafed wires, moisture, or corrosion.

3. 3

   Verify the sensor supply voltage to ensure the 5-volt sensor network is stable and free of electrical irregularities.

1. 1

   Prep the Machine

   Park the machine on a level surface, turn off the engine, and disconnect the battery to prevent electrical shorts. Allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the Lambda sensor on the exhaust system (typically mounted near the EGR exhaust treatment area or DPF/catalyst).

3. 3

   Remove Obstructions

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

4. 4

   Disconnect and Remove

   Unplug the sensor's electrical connector. Use an oxygen sensor socket or wrench to unscrew the faulty Lambda sensor from the exhaust pipe.

5. 5

   Install the New Sensor

   Thread the new Lambda sensor into the exhaust pipe by hand to prevent cross-threading, then tighten it securely. (Note: Ensure any gasket maker used nearby is 'oxygen sensor safe' to prevent contamination).

6. 6

   Reconnect

   Plug the electrical connector back into the engine harness and reinstall any heat shields.

7. 7

   Reset the ECU

   Reconnect the battery. Using a compatible diagnostic tool (such as the CNH Electronic Service Tool, Jaltest, or Bosch ESI[truck]), navigate to the engine controller and perform the 'Replacement of the Lambda Sensor – Reset ECU Data' procedure. This clears the learned calibration values and the fault code.