Case IH 19548 – Engine Control Module (ECM) / Engine ECU: SRC Min error for the NOx signal

This fault code indicates a Signal Range Check (SRC) Minimum error for the Nitrogen Oxide (NOx) sensor. It means the Engine Control Module (ECM) is receiving a voltage or signal from the NOx sensor that is below the minimum expected threshold. This is typically caused by an internal failure of the NOx sensor probe, a short to ground in the sensor's wiring circuit, or a severely degraded sensor element that can no longer accurately read exhaust gases.

• Tier 4b
• Maxxum
• Puma
• Optum
• Magnum
• Steiger

1. 1

   Inspect the wiring harness connecting the NOx sensor control module to the main engine harness for chafing, melted insulation, or corrosion.

2. 2

   Disconnect the NOx sensor module and verify it is receiving proper operating voltage (12V or 24V) and has a solid ground.

3. 3

   Inspect the exhaust pipe upstream of the NOx sensor for leaks that could introduce ambient oxygen and skew readings.

4. 4

   Connect the CNH Electronic Service Tool (EST) and monitor live NOx sensor data (ppm) to see if the reading is stuck at 0 ppm or a static minimum value.

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent voltage spikes to the ECM.

2. 2

   Locate the Sensor

   Identify the faulty NOx sensor. FPT engines utilize an Upstream (Pre-SCR) and Downstream (Post-SCR) sensor. Use your diagnostic tool to confirm which sensor is flagging the SRC Min error (often the downstream sensor).

3. 3

   Disconnect

   Unplug the electrical connector at the NOx sensor control module.

4. 4

   Remove Module

   Unbolt the NOx sensor control module box from its mounting bracket on the chassis or exhaust shield.

5. 5

   Remove Probe

   Using a 22mm NOx sensor socket or wrench, carefully unscrew the sensor probe from the exhaust pipe. Tip: If the sensor is seized, apply penetrating oil and allow it to soak. Heat may be required.

6. 6

   Install New Sensor

   Thread the new NOx sensor probe into the exhaust bung. (Most OEM sensors come with anti-seize pre-applied to the threads; if not, apply a high-temp, sensor-safe anti-seize). Torque to OEM specification (typically ~50 Nm / 37 lb-ft).

7. 7

   Mount and Route

   Secure the new control module to the bracket. Route the wiring lead carefully, ensuring it is secured away from direct contact with the hot exhaust pipe to prevent future melting.

8. 8

   Reconnect

   Plug in the electrical connector and reconnect the battery.

9. 9

   Software Reset

   Connect the CNH EST diagnostic tool. Clear the 19548 / P2201 fault codes. You may need to perform a 'NOx Sensor Replacement' reset or adaptation routine in the software to clear the learned offset values.