Case IH 19506 – Engine Control Unit (ECU): Status byte error, Sensor Temperature Not okay

This is an emissions-related fault code specific to the Selective Catalytic Reduction (SCR) and Diesel Exhaust Fluid (DEF) system. It indicates that the temperature reading from the Downstream NOx Sensor is invalid, out of range, or failing to report correctly.

• Tier 4b
• Steiger
• Magnum
• Puma
• Optum
• Maxxum
• Farmall
• Axial-Flow
• N-Series Backhoe Loaders
• Wheel Loaders (1021G)

1. 1

   Check for accompanying downstream NOx sensor codes (such as 19503 or 19504). If multiple downstream codes are present, sensor failure is highly likely.

2. 2

   Visually inspect the Downstream NOx sensor's wiring harness and connector for melting, chafing, or corrosion.

3. 3

   Use the CNH Electronic Service Tool (EST) to monitor live temperature data of the downstream NOx sensor. Extreme default readings (e.g., -40°C or 1000°C+) or erratic fluctuations indicate the sensor's internal heating circuit has failed.

4. 4

   Check the exhaust system for severe leaks before the sensor, which can skew temperature readings and trigger plausibility faults.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Locate the Sensor

   Find the Downstream NOx sensor on the exhaust tailpipe, located after the Diesel Oxidation Catalyst (DOC) and the SCR catalyst.

3. 3

   Disconnect Wiring

   Unplug the electrical connector linking the NOx sensor to the engine harness. Check the harness-side pins to ensure they are not pushed back or corroded.

4. 4

   Remove the Sensor

   Using a specialized NOx sensor socket (or a 22mm wrench), carefully unscrew the sensor from the exhaust bung. Tip: Exhaust sensors frequently seize; apply penetrating oil and allow it to soak if the sensor is stuck.

5. 5

   Install the New Sensor

   Apply a small amount of anti-seize compound to the threads of the new sensor (avoid getting any on the sensor tip). Thread it into the exhaust bung and torque to OEM specifications.

6. 6

   Reconnect

   Plug the new sensor's electrical connector into the engine harness and secure the wiring away from extreme heat sources.

7. 7

   Clear Codes & Test

   Reconnect the battery. Connect the CNH EST diagnostic tool, clear fault code 19506, and run an SCR system test or a forced stationary regeneration to verify the sensor reaches operating temperature and the code does not return.