Case IH 3719 – Engine Control Module (ECM): Fault check for sigma exceeding maximum limit

Fault code 3719 indicates a 'Fault check for sigma exceeding maximum limit' related to the exhaust Lambda (Oxygen / O2) sensor. The ECU continuously monitors this sigma value to ensure the sensor is operating within its calibrated limits. When the sigma value exceeds the maximum programmed threshold, the ECU determines that the sensor's signal is implausible, out of calibration, or that the sensor has internally failed.

• Steiger
• Magnum
• Puma
• Maxxum
• Farmall
• Axial-Flow

1. 1

   Inspect the lambda sensor wiring harness and connectors for damage, melted insulation, corrosion, or loose pins (especially Nernst cell, pump current, and virtual ground pins).

2. 2

   Check for exhaust leaks upstream of the lambda sensor near the turbocharger downpipe or exhaust manifold, as unmetered oxygen can skew readings.

3. 3

   Verify the sensor's internal heater circuit is functioning, as it must reach approximately 780°C to provide accurate readings.

4. 4

   Check with a CNH Electronic Service Tool (EST) for any pending Engine ECU software updates that might adjust lambda sensor diagnostic calibration limits.

1. 1

   Turn off machine

   Turn off the machine, remove the key, and disconnect the negative battery cable.

2. 2

   Locate lambda sensor

   Locate the lambda (O2) sensor on the exhaust system (typically mounted on the turbocharger downpipe or near the DPF/SCR inlet).

3. 3

   Disconnect electrical connector

   Disconnect the sensor's electrical connector from the main engine harness.

4. 4

   Remove lambda sensor

   Using a specialized O2 sensor socket (usually 22mm or 7/8"), carefully loosen and remove the lambda sensor from the exhaust pipe. Note: If the sensor is seized, apply penetrating oil to the threads and allow it to soak before attempting removal to prevent damaging the exhaust bung threads.

5. 5

   Inspect and clean threads

   Inspect the threads in the exhaust pipe and clean them with a thread chaser if necessary.

6. 6

   Apply anti-seize

   Apply a small amount of high-temperature anti-seize compound to the threads of the new lambda sensor (many OEM Bosch sensors come with this pre-applied). Do not get anti-seize on the sensor tip.

7. 7

   Install new sensor

   Thread the new lambda sensor in by hand to prevent cross-threading, then tighten to the OEM torque specification using a torque wrench.

8. 8

   Reconnect electrical connector

   Reconnect the electrical connector and ensure the wiring is routed and secured away from extreme heat sources or moving parts.

9. 9

   Clear codes and test

   Reconnect the battery, connect the CNH EST diagnostic tool, clear the fault codes, and run the engine through a heat cycle to verify the code does not return.