Case IH 3530 – Engine Control Module (ECM) / Engine Management System (EMS): Downstream NOx sensor internal failure (Heater Short Circuit Error)

The downstream Nitrogen Oxide (NOx) sensor is located in the exhaust stream after the Selective Catalytic Reduction (SCR) catalyst. This sensor contains an internal heating element designed to quickly bring it up to operating temperature so it can accurately measure the pollutants exiting the tailpipe. This fault code triggers when the system detects a short circuit within this heater circuit, meaning the sensor cannot heat up properly and the SCR system cannot verify emissions compliance.

• Steiger T4B
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Titan Series Floaters (3030, 3530, 4030, 4530)
• Farmall (110A-140A)
• Puma (150-220)
• Magnum (180-380)
• Maxxum
• Optum

1. 1

   Inspect the wiring harness leading to the downstream NOx sensor for melted wires, chafing against the exhaust or chassis, or physical damage.

2. 2

   Disconnect the NOx sensor and inspect the pins on both the machine side and the sensor side for corrosion, moisture intrusion, or bent pins.

3. 3

   Verify that the sensor connector is receiving the proper supply voltage and ground from the ECM.

4. 4

   Confirm internal failure: if the machine-side wiring harness and voltages are intact, the sensor itself has failed internally and must be replaced.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical spikes during the repair. Ensure the exhaust system has completely cooled down.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor, which is mounted in the exhaust pipe directly after the SCR catalyst / tailpipe area.

3. 3

   Disconnect

   Unplug the electrical connector for the NOx sensor and unclip the wiring harness from any retaining brackets.

4. 4

   Removal

   Use a specialized NOx/O2 sensor socket or wrench to unscrew the sensor from the exhaust pipe. (Note: Penetrating oil may be required if the sensor threads are seized from exhaust heat).

5. 5

   Installation

   Apply a small amount of anti-seize to the threads of the new sensor (if not pre-applied by the manufacturer) being careful not to get any on the sensor tip. Thread the new sensor into the exhaust pipe and tighten to OEM torque specifications.

6. 6

   Reconnect

   Route the wiring harness exactly as it was from the factory, ensuring it is secured away from extreme heat sources. Reconnect the electrical plug.

7. 7

   Relearn/Clear Codes

   Reconnect the battery. Connect a diagnostic scan tool to clear the 3530 (DTC E26E) fault code.

8. 8

   Warm-Up Cycle

   Start the engine and allow it to run through a warm-up cycle. The ECM must wick moisture off the tip of the sensor (dew point warm-up cycle) before the sensor status changes from "Not Ready" to "Ready". Verify the fault code does not return once the system is ready.