Case IH 3400 – Engine Control Unit (ECU) / EDC (Electronic Diesel Control): Lambda sensor : Lambda Sensor inner Resistance calibration value too High

The engine control system has detected an abnormally high electrical resistance within the Lambda (Oxygen/O2) sensor's internal circuitry (typically the heater circuit or the measuring cell). This generally points to a degraded sensor element, a burnt-out internal heater, or an open circuit/poor connection in the wiring harness.

• Farmall
• Maxxum
• Puma
• Magnum
• Combine Harvesters

1. 1

   Inspect the Lambda sensor wiring harness and connectors for melted wires, chafing, corrosion, or loose pins.

2. 2

   Disconnect the Lambda sensor and use a multimeter to measure the internal resistance of the sensor's heater circuit. If it reads as an open circuit (OL) or is significantly higher than OEM spec, the sensor is internally faulty.

3. 3

   Check the continuity of the wiring between the Lambda sensor connector and the EDC/ECU pins to ensure there is no break in the harness.

4. 4

   Turn the key to the ON position and verify that the sensor connector is receiving the correct supply voltage (12V) and has a solid ground.

1. 1

   Preparation

   Turn off the engine, remove the key, 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 gas aftertreatment system (typically mounted on the exhaust pipe upstream of the catalyst/DPF).

3. 3

   Removal

   Disconnect the sensor's electrical connector. If necessary, loosen any surrounding heat shields. Use a specialized O2 sensor socket or wrench to carefully unscrew the sensor from the exhaust pipe.

4. 4

   Installation

   Apply a small amount of high-temperature anti-seize compound to the threads of the new Lambda sensor (many new Bosch sensors come with this pre-applied). Thread the new sensor in by hand to prevent cross-threading, then tighten to the manufacturer's torque specification.

5. 5

   Reassembly

   Reconnect the electrical connector and secure the wiring harness away from extreme heat sources. Reinstall any heat shields.

6. 6

   Calibration/Reset

   Reconnect the battery. Connect a compatible diagnostic tool (such as CNH EST or Jaltest) to the machine and clear the fault codes. Depending on the specific EDC version (e.g., EDC17), you may need to perform a 'Lambda/O2 sensor reset' via the diagnostic software so the ECU learns the new sensor's calibration values.