Case IH F-4378-02 - ECU – Engine Control Unit (ECU): NH3 sensor signal is not changing

The aftertreatment SCR ammonia (NH3) sensor output has flatlined or frozen, indicating either a faulty NH3 sensor (damaged, improperly installed, or missing) or a hardware/software failure in the NH3 control unit (Module A-087).

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Magnum
• Maxxum
• Puma
• Optum
• Steiger
• Luxxum
• 580N Backhoe Loader

1. 1

   Verify that the tractor battery power supply has not been connected to an external power supply. If an external power supply is connected, disconnect it and test the system for normal operation.

2. 2

   Remove and inspect the NH3 sensor probe for debris accumulation, sensing tip breakage, or other physical damage. There should be no accumulation or breakage.

3. 3

   Disconnect the slide-lock connector and remove the NH3 sensor probe from the NH3 sensor module. Use a digital multimeter to measure the trim resistance of the NH3 sensor probe. The trim resistance must measure between 500 and 2000 ohms.

1. 1

   Safety Prep

   Wait for the aftertreatment system to completely cool down before working on the hot exhaust components to prevent severe burns.

2. 2

   Disconnect Power

   Ventilate the battery compartment. Disconnect the batteries to prevent arcing, removing the negative (-) battery cable first.

3. 3

   Isolate the Component

   Locate the NH3 sensor assembly on the SCR catalyst. Disconnect the slide-lock connector separating the sensor probe from the sensor module.

4. 4

   Replace the Faulty Component

   If the probe failed the visual inspection or the multimeter resistance test (outside 500-2000 ohms), replace only the NH3 sensor probe. If the probe tests within specification, the fault lies within the NH3 sensor module (Control Unit A-087). Replace the sensor module.

5. 5

   Reassembly

   Install the new component, reconnect the slide-lock connector, and reattach the battery cables (attaching the negative cable last).

6. 6

   Clear Codes

   Turn the key on and use the diagnostic display or service tool to clear the inactive fault codes and verify the sensor signal is now fluctuating normally during operation.