New Holland 3715 – ECU: Lambda Sensor - SRC Low Error for O2 Calibration

The Engine Control Unit (ECU) has detected a low error in the Sensor Reference Circuit (SRC) during the oxygen (O2) calibration process. This indicates that the voltage or reference signal received from the Lambda sensor is below the expected threshold. This condition prevents proper sensor calibration, which is critical for maintaining the correct air-fuel ratio for optimal engine performance and emissions control. It is typically caused by a faulty sensor, wiring harness issues, or a failing sensor heater circuit.

• T4
• T5
• WORKMASTER
• BOOMER
• C227
• C232
• C238
• TR270
• TR310
• TV380
• TR320
• L221
• L223
• L225
• L228
• L230
• W50C
• W60C
• W70C
• W80C
• B95C
• B95CLR
• B95CTC
• B110C
• FARMALL series

1. 1

   Visually inspect the Lambda sensor, its connector, and the wiring harness for physical damage, corrosion, or loose connections

2. 2

   Inspect the exhaust system for any leaks between the engine and the Lambda sensor that could alter oxygen readings

3. 3

   Verify machine battery voltage is stable and within the correct operating range, as low voltage can trigger sensor faults

4. 4

   Measure the sensor's heater circuit resistance with a multimeter (engine off, sensor disconnected). Resistance should typically be between 5 and 20 Ohms across the heater wires

5. 5

   Back-probe the sensor's signal wire (often black) with the engine running at operating temperature. Voltage should fluctuate rapidly between approximately 0.1V and 0.9V

6. 6

   Use the CNH Electronic Service Tool (EST) to monitor real-time Lambda sensor data and response

1. 1

   Retrieve and document codes

   Use a diagnostic tool to confirm fault code 3715 is active and check for any other related codes.

2. 2

   Perform diagnostic checks

   Complete the recommended diagnostic checks to rule out wiring problems, low battery voltage, or exhaust leaks.

3. 3

   Replace the Lambda sensor

   If diagnostics point to a faulty sensor, replace the Lambda sensor assembly.

4. 4

   Clear fault codes

   Use the diagnostic tool to clear all fault codes from the ECU after component replacement.

5. 5

   Perform sensor calibration

   Use the CNH Electronic Service Tool (EST) to calibrate the new sensor and teach the ECU the new parameters. Failure to calibrate will likely result in the fault code returning.

6. 6

   Verify the repair

   Start the engine, allow it to reach operating temperature, and monitor the sensor's performance with the diagnostic tool to ensure the code does not reappear.