Case IH 3170 – Engine Control Unit (ECU) / NH3 Control Unit (A-087): NH3 (Ammonia) sensor signal is not changing over time

The NH3 (Ammonia) sensor signal is not changing over time. The system expects the sensor's readings to fluctuate as exhaust gas composition changes during operation. When the signal is stuck at a constant value, the system flags a failure. Possible failure modes include a faulty NH3 sensor that is damaged, improperly installed, or missing, or a hardware or software failure in the NH3 control unit (A-087).

• Steiger T4B
• 240 Series Axial-Flow
• 7240
• 8240
• 9240
• 6150
• 8250
• Magnum
• Puma
• Maxxum
• Steiger
• Quadtrac

1. 1

   Check for related SCR codes (such as DTC-43CE) using a diagnostic tool and diagnose those concurrently if present.

2. 2

   Inspect the NH3 sensor physically for debris accumulation, sensing tip breakage, or other physical damage.

3. 3

   Visually inspect the relevant harnesses and connectors for damage, bent or dislocated pins, corroded terminals, or broken wires. Verify connectors are fully seated.

4. 4

   Perform a wiggle test by flexing the involved wiring harnesses to reveal intermittent breaks or shorts while monitoring the display for changes.

5. 5

   Check the ECU for the appropriate software version and re-flash if necessary.

1. 1

   Resolve Physical Damage

   If the NH3 sensor is physically damaged or heavily fouled with debris, replace the sensor.

2. 2

   Repair Wiring

   If the harness inspection reveals shorts or broken wires, repair the damaged conductor or connector.

3. 3

   Clear the Code

   If no damage is found and the display indicates normal readings after checking connections, erase the fault code.

4. 4

   Perform SCR Fault Repair Verification

   Because this fault causes an engine inducement (power derate/power loss), you must perform the SCR Fault Repair Verification Test using the Electronic Service Tool (EST) once the physical repair is complete.

5. 5

   Reset Engine Restart Counter

   You must perform the 'Engine Restart Counter Reset / Unlock Inducement' configuration with the EST before you can return the machine to service and restore full engine power.