Deutz-Fahr 693 – EMR4: NOx Signal Readiness Monitoring Fault

The engine control unit (EMR4) is unable to verify the operational readiness of the NOx sensor system due to missing detailed information. The sensor data is valid but reading above the normal operating range (FMI 0). Consequently, the ECU cannot confirm if the NOx sensor is providing the correct and plausible data required for the proper functioning and regulation of the SCR emissions monitoring system.

• Agrotron Serie 5
• Agrotron Serie 6
• Agrotron Serie 7
• Agrotron Serie 8
• Agrotron Serie 9
• TCD 2.9 L04
• TCD 3.6 L04

1. 1

   Read all active and stored fault codes, along with freeze-frame data, using a diagnostic tool (Deutz SerDia or J1939 scanner).

2. 2

   Visually inspect the NOx sensor wiring harness (both upstream and downstream of the SCR catalyst) for chafing, melting from exhaust heat, corrosion at connector pins, or loose connections.

3. 3

   Test the sensor heater circuit: with a cold engine, disconnect the NOx sensor and measure resistance between the heater circuit pins (should be 2 to 6 ohms). Values outside this range indicate a defective heating element.

4. 4

   Analyze live NOx data (in ppm) with a warm engine: the upstream sensor should read 150-400 ppm at idle, while the downstream sensor should be significantly lower (indicating 85-95% SCR efficiency). Fixed values (e.g., 0 ppm) or implausible readings indicate a faulty sensor.

5. 5

   Perform a dynamic test via forced DPF regeneration: if upstream and downstream NOx values are not roughly equal during regeneration (when no AdBlue is injected), one of the sensors is likely defective.

1. 1

   Determine sensor position

   Use live data analysis to identify whether the upstream (before SCR) or downstream (after SCR) NOx sensor is causing the fault, as the code itself may not specify.

2. 2

   Remove defective sensor

   Allow the exhaust system to cool completely. Apply penetrating oil to the sensor threads and let it soak to ease removal.

3. 3

   Prepare new sensor

   Apply a small amount of ceramic anti-seize paste to the threads of the new sensor, ensuring absolutely no paste gets on the sensor tip.

4. 4

   Install and torque sensor

   Thread the new sensor in by hand, then tighten it to the manufacturer's specified torque (typically 40 to 60 Nm).

5. 5

   Route wiring harness

   Connect the sensor plug and securely route the wiring harness in the original brackets, ensuring adequate clearance from hot exhaust components and avoiding kinks.

6. 6

   Clear codes and calibrate

   Clear all emissions-related fault codes using a diagnostic tool. Perform a calibration drive (e.g., highway driving for at least 10 minutes at over 80 km/h) to allow the SCR system to relearn.