New Holland ENG 3521 – Engine Control Unit (ECU) / EDC / EDC7: NOx Estimation failure - Estimated Nox signal not reliable

The engine control system is receiving an implausible or unreliable signal from the Nitrogen Oxide (NOx) sensor, or the estimated NOx levels do not align with expected parameters. The system cannot properly verify the efficiency of the SCR (Selective Catalytic Reduction) system.

• New Holland T6 Series (T6.125, T6.145, T6.155, T6.165, T6.175, T6.180)
• New Holland T7 Series (T7.165S, T7.175, T7.190, T7.210, T7.225, T7.230, T7.245, T7.260, T7.270)
• New Holland T8 Series (T8.320, T8.350)

1. 1

   Check for accompanying codes (e.g., 3528, 3529, 3530, 3532, 3533) to isolate whether the issue is a dead sensor, a wiring short, or a CAN-bus communication failure

2. 2

   Inspect the wiring harness and connectors leading to the NOx sensor control unit for damage, corrosion, or loose connections

3. 3

   Inspect the exhaust system for leaks prior to the NOx sensor, as leaks can alter the exhaust gas composition and cause unreliable readings

4. 4

   Check the AdBlue/DEF dosing system to ensure it is functioning correctly, as poor DEF injection can lead to actual NOx levels that trigger an estimation failure

1. 1

   Locate the Sensor

   Identify the faulty NOx sensor on the exhaust system. It is typically mounted near the DPF (Diesel Particulate Filter) or SCR catalyst.

2. 2

   Disconnect Power

   Turn off the machine and disconnect the electrical harness from the NOx sensor's control module.

3. 3

   Remove the Sensor

   Carefully unscrew the NOx sensor probe from the exhaust pipe. (Note: Penetrating oil may be required if the sensor is seized due to high exhaust temperatures).

4. 4

   Install the New Sensor

   Thread the new NOx sensor probe into the exhaust system and tighten it securely.

5. 5

   Mount the Control Unit

   Secure the attached NOx sensor control module to its mounting point and reconnect the electrical harness.

6. 6

   Clear Fault Codes

   Use a diagnostic tool or DTC eraser to clear the ENG 3521 fault code from the Engine ECU.

7. 7

   Test Run

   Start the engine and perform a test run to ensure the check engine light remains off and the emissions system is operating within normal parameters.