Case IH 3529 – Engine Control Unit (ECU) / Engine Management System (EMS) or Aftertreatment Control Module (ACM / DCU): Downstream NOx sensor internal failure (Heater Open Circuit Error)

The downstream NOx sensor contains an internal heating element used to boil off moisture (dew point) and bring the sensor up to operating temperature. An open circuit error means the electrical path for this heater is broken, either internally within the sensor itself or in the wiring harness leading to it.

• Steiger T4B
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• 5140 Combine
• 6140 Combine
• 7140 Combine
• Magnum (180 through 380)
• Steiger 4WD and Quadtrac (350 through 620)
• Maxxum (115 through 150)
• Puma (150 through 220)
• Farmall (110A through 140A)

1. 1

   Inspect the wiring harness and FEM TERM MCON connectors leading to the downstream NOx sensor for severed wires, corrosion, or disconnected lines.

2. 2

   Connect a diagnostic tool and view the 'Dew Point' parameter for the emissions sensors. It should transition from 'not ready' to 'Ready' if the heater circuit is functioning.

3. 3

   Perform a warm-up cycle test by turning the key switch ON, OFF, then ON again. If the code immediately returns as an active open load, the internal heater is permanently failed.

1. 1

   Power Down

   Turn off the engine and disconnect the battery to prevent electrical shorts.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor on the exhaust system. It is positioned directly after the SCR catalyst.

3. 3

   Disconnect

   Unplug the electrical connector linking the NOx sensor to the machine's wiring harness.

4. 4

   Remove

   Use a sensor socket or wrench to carefully unscrew the faulty NOx sensor from the exhaust pipe.

5. 5

   Install

   Thread the new NOx sensor into the exhaust pipe and tighten it to the OEM torque specification.

6. 6

   Reconnect

   Plug the new sensor's electrical connector into the harness.

7. 7

   Clear and Relearn

   Reconnect the battery, clear the inactive fault codes using a diagnostic tool, and run the engine through a warm-up cycle so the ECU can verify the new sensor's heater is operating and the 'Dew Point' parameter reaches 'Ready'.