Case IH 3525 (DTC E18E) - ECU – Engine Control Unit (ECU): Downstream NOx sensor internal failure (Open Circuit Error)

This code indicates an internal open circuit failure within the downstream Nitrogen Oxide (NOx) sensor. The downstream NOx sensor is located directly after the Selective Catalytic Reduction (SCR) catalyst in the exhaust system. It measures the pollutants making it through the Diesel Oxidation Catalyst (DOC) and SCR to ensure the emissions system is regulating DEF (Diesel Exhaust Fluid) dosing and SCR efficiency correctly. An open circuit means the control module has lost electrical continuity with the sensor's internal circuitry.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Farmall (110A-140A)
• Magnum (180-380)
• Maxxum (115-150)
• Puma (140-240)
• Optum (270-300 CVX)
• Steiger/Quadtrac (370-620)
• T-Series equivalents
• N-Series Loader Backhoes
• Wheel Loaders (1021G Tier 4B)

1. 1

   Inspect the wiring harness leading to the downstream NOx sensor for physical damage, chafing, or disconnected lines

2. 2

   Check the 5-pin terminal connector for corrosion, pushed-out pins, or moisture

3. 3

   Verify that the sensor is receiving proper power and ground from the ECU

4. 4

   Ensure there are no accompanying CAN timeout errors (such as DTC 3533 / 9D6E), which would indicate a broader network issue rather than an internal sensor failure

5. 5

   Check the sensor's 'dew point' warm-up cycle on a diagnostic tool; it will read 'Not Ready' until exhaust heat wicks moisture off the tip. Do not mistake this normal delay for a failed sensor

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical shorts and allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor, which is threaded into the exhaust pipe directly after the SCR catalyst.

3. 3

   Disconnect Wiring

   Unplug the electrical connector linking the NOx sensor to the main engine/rear chassis harness.

4. 4

   Remove the Sensor

   Using an appropriate sensor socket or wrench, carefully unscrew the failed NOx sensor from the exhaust pipe.

5. 5

   Install the New Sensor

   Thread the new OEM downstream NOx sensor into the exhaust bung. Tighten to the manufacturer's specified torque to prevent exhaust leaks.

6. 6

   Reconnect Wiring

   Plug the sensor's electrical connector back into the machine's harness, ensuring the locking tab clicks into place.

7. 7

   Clear Codes and Test

   Reconnect the battery. Connect a diagnostic service tool, clear the inactive 3525 (E18E) fault code, and start the engine. Allow the engine to run until the exhaust reaches operating temperature and the sensor status changes from 'Not Ready' to 'Ready' to verify the repair.