Case IH F-519045-02 - ECU – Engine Control Unit (ECU / EDC) or Denox Module (DCU15): Downstream NOx sensor values are not plausible

The engine's aftertreatment system is receiving erratic, intermittent, or completely implausible readings from the NOx sensor located downstream of the Selective Catalytic Reduction (SCR) catalyst. The system uses this sensor to measure the pollutants making it through the Diesel Oxidation Catalyst (DOC) and SCR to regulate Diesel Exhaust Fluid (DEF) dosing.

• MAGNUM AFS Connect
• Magnum (180-370, AFS Connect)
• Puma (130-230)
• Maxxum (110-140)
• Steiger (350-600)
• Quadtrac
• Farmall
• 240 Series Axial-Flow Combines (5130-9230)
• Austoft 9900
• Farmlift series
• N-Series TLBs
• Wheel Loaders (521F-1121F)

1. 1

   Check for accompanying codes: Resolve any upstream NOx sensor faults (e.g., DTC-E98E) or SCR catalyst efficiency faults (e.g., DTC-2DDA) first, as they can skew downstream readings

2. 2

   Check the functioning of the Denox controller (DCU15) and its voltage supply, and verify its CAN configuration presence on the network

3. 3

   Visually inspect the downstream NOx sensor harnesses and connectors for damage, bent or dislocated pins, corroded terminals, or broken wires

4. 4

   Perform a flex test on the involved harnesses while monitoring the diagnostic display to reveal intermittent breaks or shorts

5. 5

   Perform a drive cycle test (engine speed >1600 RPM with constant periods of ~5 seconds and >5 motoring phases >10 seconds in highest gear) and check OBD readiness

1. 1

   Secure the Machine

   Park the machine on a level surface, turn off the engine, and allow the exhaust system (DOC/SCR) to cool completely to avoid severe burns.

2. 2

   Inspect and Repair Wiring

   If the diagnostic flex test revealed a wiring issue, repair the shorted or broken conductor in the harness. Verify that the connectors are fully seated and locked.

3. 3

   Remove the Sensor

   If the wiring is intact, the downstream NOx sensor has failed internally. Disconnect the sensor's 5-pin MCON electrical connector from the harness. Unscrew the NOx sensor probe from the exhaust pipe (located directly after the SCR catalyst).

4. 4

   Install the New Sensor

   Thread the new downstream NOx sensor into the exhaust bung and tighten to OEM torque specifications. Route the wiring safely away from extreme heat sources and plug the connector back into the harness.

5. 5

   Clear Codes

   Connect your diagnostic scanner (e.g., Case IH EST) and clear the inactive fault codes. Error cleaning is required after fitting a new NOx sensor to reset the aftertreatment plausibility monitors.

6. 6

   Verify Repair

   Run the machine through a standard operating cycle to ensure the DEF system doses correctly and the code does not return.