Case IH 19545 – Engine Control Module (ECM / ECU): Plausibility error during Rich to Lean switch over

An emissions-related fault indicating that the Engine Control Unit (ECU) has detected that the NOx (Nitrogen Oxide) sensor's readings are out of the expected range or reacting improperly when the exhaust gas transitions from a rich state to a lean state. This typically points to a failing NOx sensor, an exhaust leak, or an issue with the DEF (AdBlue) dosing system skewing the sensor's readings.

• Tier 4b
• Maxxum
• Puma
• Optum
• Farmall
• Luxxum
• 1650M Crawler Dozers
• N Series Backhoe Loaders
• 580 ST
• 590 ST
• 695 ST

1. 1

   Inspect the NOx sensor wiring harness and pins for corrosion, melting, or loose connections (often accompanied by open/short circuit codes like 19549 or 19551).

2. 2

   Check for exhaust leaks upstream of the NOx sensor, as unmetered oxygen entering the exhaust stream will skew rich/lean readings.

3. 3

   Verify that the DEF (AdBlue) tank is full of uncontaminated fluid and that the DEF supply pump and injector are functioning correctly.

4. 4

   Connect a heavy-duty diagnostic tool to monitor live NOx sensor data and perform a sensor plausibility test.

1. 1

   Power Down

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

2. 2

   Locate the Sensor

   Identify the faulty NOx sensor on the exhaust aftertreatment system. Verify via your diagnostic tool whether the upstream or downstream sensor is logging the error.

3. 3

   Disconnect

   Unplug the electrical connector for the NOx sensor from the main engine harness.

4. 4

   Removal

   Apply penetrating oil to the sensor threads if it is seized. Carefully remove the sensor using a specialized NOx/O2 sensor socket to avoid stripping the exhaust pipe bung.

5. 5

   Installation

   Clean the exhaust pipe threads. Install the new NOx sensor and torque it to the manufacturer's specifications.

6. 6

   Reconnect

   Plug the electrical connector back into the harness and reconnect the battery.

7. 7

   Software Reset

   Connect your diagnostic tool and clear the 19545 fault code. If the machine was forced into a torque/RPM derate, you must perform a 'Startup counter reset' or inducement mode reset via the diagnostic tool to restore full engine power.