Case IH 19188 – Engine Control Unit (ECU) or Vehicle Control Module (VCM): Upstream NOx sensor self-diagnosis result is lower than the limit.

The upstream Nitrogen Oxide (NOx) sensor is failing its internal self-diagnostic check and reading lower than the expected engine-out emissions threshold.

• Tier 4b
• 240 Series Axial-Flow Combines
• 5140
• 6140
• 7140
• 7240
• 8240
• 9240
• Magnum (180-340)
• Puma (150-210)
• Steiger
• Optum
• Farmall
• Patriot (2250-4440)
• Titan
• N-Series TLBs
• Farmlift

1. 1

   Inspect the upstream NOx sensor wiring harness and connector (e.g., Connector C186) for melted wires, corrosion, or loose terminal pins

2. 2

   Inspect the exhaust piping between the engine turbocharger and the DOC/SCR for any leaks (an exhaust leak introduces fresh air, which dilutes the exhaust gas and causes the upstream NOx sensor to read artificially low)

3. 3

   Ensure the DEF tank is not contaminated with diesel fuel or water, which can trigger cascading SCR faults

4. 4

   Verify that the sensor is receiving proper voltage (typically 12V or 24V depending on the machine) and communicating on the CAN bus network

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical shorts and ensure the exhaust system has completely cooled down.

2. 2

   Locate the Sensor

   Locate the upstream NOx sensor. It is threaded into the exhaust pipe before the DOC and SCR catalyst assembly.

3. 3

   Disconnect Wiring

   Unplug the electrical connector linking the NOx sensor to the machine's wiring harness. Unclip the wire routing from any heat shields.

4. 4

   Remove the Sensor

   Using a specialized 7/8" (22mm) O2/NOx sensor socket, carefully unscrew the sensor from the exhaust bung. Note: If the sensor is seized, apply penetrating oil to the threads and allow it to soak to prevent stripping the exhaust bung.

5. 5

   Clean the Threads

   Use a thread chaser to clean the exhaust pipe bung threads to ensure the new sensor seats correctly.

6. 6

   Install the New Sensor

   Thread the new upstream NOx sensor in by hand to prevent cross-threading, then torque it to the manufacturer's specification.

7. 7

   Route the Wiring

   Reconnect the electrical connector and secure the wiring harness exactly as it was from the factory, ensuring it is kept away from extreme exhaust heat sources.

8. 8

   Clear Codes & Test

   Reconnect the battery. Use the CNH Electronic Service Tool (EST) to clear the 19188 fault code. Run the engine through a forced regeneration or a standard operating drive cycle to verify the sensor is reading correctly and the code does not return.