Massey Ferguson 5035.31 – Engine Control Unit (ECU): Issue With Exhaust Top NOx Sensor Module. (ECU)

Malfunction, implausible reading, or communication failure with the upstream NOx sensor (also known as NOx Sensor 1 or the inlet NOx sensor). This sensor is located in the exhaust stream before the Selective Catalytic Reduction (SCR) catalyst and Diesel Oxidation Catalyst (DOC).

• 4710
• 7724S
• 5712SL
• 7722S
• 7722
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 4708
• 7726S
• 4707
• 4709
• 5711SL
• 7718S
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 7720
• Tier 4 (2015-2021)
• 7715S
• 7724
• 5608-5613
• 5708-5713
• 6612-6616
• 6711-6718
• 7614-7626
• 7714-7726
• 8670-8690
• 8727-8740
• 7340
• 7344
• 7345
• 7347
• 7360
• 7370

1. 1

   Inspect the wiring harness leading to the upstream NOx sensor for chafing, heat soak damage, or vibration wear

2. 2

   Check for any exhaust leaks between the engine manifold and the NOx sensor, as fresh air entering the exhaust stream will skew readings

3. 3

   Ensure the DEF tank is at least one-third full and contains clean, ISO 22241-compliant DEF

4. 4

   Look for other active codes related to the DEF pump, DEF injector, or DOC temperatures (e.g., 004374.xx, 004792.xx) which can cause the ECU to flag NOx readings as implausible

1. 1

   Power Down

   Turn off the tractor, remove the key, and disconnect the battery to prevent electrical spikes to the ECU.

2. 2

   Locate the Sensor

   Locate the upstream NOx sensor on the exhaust pipe, positioned before the DOC/SCR catalyst assembly.

3. 3

   Remove the Sensor

   Disconnect the 5-pin electrical connector. Use a specialized NOx sensor socket or a 22mm wrench to carefully unthread the sensor from the exhaust bung. (If seized, apply penetrating oil and allow it to sit).

4. 4

   Prepare the New Sensor

   If the new sensor does not have anti-seize pre-applied to the threads, apply a small amount of high-temperature anti-seize. Crucial: Do not get any anti-seize on the sensor probe tip, as this will permanently ruin the sensor.

5. 5

   Installation

   Thread the new sensor into the exhaust bung by hand to prevent cross-threading, then tighten to the manufacturer's torque specification.

6. 6

   Route the Harness

   Reconnect the electrical connector. Route the wiring harness exactly like the factory routing to keep it away from extreme exhaust heat and high-vibration areas.

7. 7

   Clear Codes & Calibrate

   Reconnect the battery. Use an AGCO diagnostic tool (EDT) to clear the fault codes. Depending on the ECU software version, you may need to run a NOx sensor calibration or reset the SCR system adaptations so the ECU recognizes the new module.