Case IH 3525 – Engine Control Unit (EDC) or Vehicle Control Module (VCM): Downstream NOx sensor internal failure (Open Circuit Error)

The system has detected an open electrical circuit within the downstream Nitrogen Oxide (NOx) sensor, which is responsible for monitoring the NOx and oxygen levels in the exhaust gas after it passes through the Selective Catalytic Reduction (SCR) catalyst.

• Steiger T4B
• 240 Series Axial-Flow Combines (5140, 6140, 7140, 7240, 8240, 9240)
• Magnum (180, 200, 220, 240, 250, 280, 310, 340)
• Puma (140, 145, 150, 165, 185, 200, 220)
• Maxxum (115, 125, 135, 145, 150)
• Farmall (110A, 120A, 130A, 140A)
• Steiger 4WD series
• Patriot (2250, 3240, 3340, 4440)
• Titan (3040, 3540, 4040, 4540)

1. 1

   Check system voltage at the battery and alternator, as low voltage (often throwing SPN 168) is a common cause of misdiagnosed stored fault codes.

2. 2

   Physically inspect the wiring harness leading to the downstream NOx sensor for chafed wires, melted insulation, or a disconnected/corroded 5-pin MCON plug.

3. 3

   Check for accompanying downstream NOx sensor codes (such as 3526, 3528, or 3529) that might help isolate the issue.

1. 1

   Power down machine

   Turn off the machine's ignition and turn off the main battery disconnect switch to ensure the exhaust system is cool and the ECU is powered down.

2. 2

   Locate sensor

   Locate the downstream NOx sensor. It is positioned in the exhaust pipe directly behind (downstream of) the SCR catalyst.

3. 3

   Disconnect harness

   Disconnect the electrical connector (typically a 5-pin plug) from the machine's wiring harness.

4. 4

   Remove sensor

   Unthread and remove the faulty NOx sensor from the exhaust pipe.

5. 5

   Install new sensor

   Install the new replacement NOx sensor into the exhaust bung and tighten it to the manufacturer's torque specification. (Note: Thread damage during removal/installation voids replacement eligibility on these sensors).

6. 6

   Reconnect harness

   Reconnect the 5-pin electrical connector to the harness.

7. 7

   Clear codes and verify

   Restore battery power, connect a diagnostic tool (such as the Case IH EST), clear the inactive 3525 fault code, and run the engine to verify the SCR system is reading NOx levels properly without throwing an open circuit error.