Case IH 3714 – ENGINE ECU (EDC - Electronic Diesel Control module): Lambda sensor: Fault code to indicate SRC High error for O2 calibration

This code indicates a Signal Range Check (SRC) High error during the oxygen (O2) calibration phase of the Lambda sensor. The Engine Control Unit (ECU) detects that the voltage or signal returning from the Lambda sensor is exceeding the maximum expected threshold during its self-calibration cycle. This typically points to a short-to-battery in the sensor wiring, a failed sensor heater circuit, or an internal failure of the sensor's measuring cell.

• Farmall
• Case IH Farmall 115U Pro EP
• Case IH Puma 210
• Case IH MX / TG Series
• Case IH SR175 Skid Steers

1. 1

   Inspect the Lambda sensor and its wiring harness for physical damage, melting from exhaust heat, or chafing

2. 2

   Disconnect the Lambda sensor and check the pins for corrosion, moisture, or pushed-out terminals

3. 3

   Use a multimeter to test the signal wires between the Lambda sensor connector and the Engine ECU for a short to voltage/battery

4. 4

   Look for accompanying Lambda sensor codes that might isolate the issue, such as 3720 (Low battery voltage at the SPI chip), 3722/3723 (LSU sensor temperature Ri out of limits), or 3711 (SCB error of the LSU Heater Power stage)

1. 1

   Power Down

   Turn off the machine and disconnect the battery ground cable to prevent any electrical spikes.

2. 2

   Locate the Sensor

   Locate the Lambda (O2) sensor on the exhaust system (usually near the DPF or exhaust manifold depending on the exact engine layout).

3. 3

   Remove the Sensor

   Disconnect the 4-pin electrical connector. Use an O2 sensor socket or a wrench to carefully unthread the Lambda sensor from the exhaust pipe. (If it is stuck, apply penetrating oil and allow it to sit).

4. 4

   Install the New Sensor

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

5. 5

   Reconnect

   Plug the electrical connector back into the engine harness, ensuring it clicks securely into place.

6. 6

   Calibrate/Clear Codes

   Reconnect the battery. Use a diagnostic scan tool (such as the CNH Electronic Service Tool) to clear the inactive 3714 fault code. Start the engine and allow it to reach operating temperature so the ECU can perform a new O2 calibration cycle and verify the repair.