Case IH 3170 (DTC 38CB) - ECU – ECU: NH3 sensor signal is not changing

The Ammonia (NH3) sensor, which monitors the Selective Catalytic Reduction (SCR) emissions system, is sending a static, frozen, or unresponsive signal to the controller, triggering an engine inducement (severe engine power loss or derate) and activating the stop engine/warning lights.

• MAXXUM T4E
• Case IH 240 Series Axial-Flow Combines
• Case IH Puma Tractors
• Case IH Magnum Tractors
• Case IH Farmall Tractors

1. 1

   Visually inspect the NH3 sensor wiring harness between the sensor and the controller for any defects, chafing, or disconnected lines.

2. 2

   Check the CAN controller of the NH3 sensor to ensure the sensor is present and correctly connected to the network.

3. 3

   Verify there is no undervoltage condition reaching the sensor.

4. 4

   Check if the sensor heating element is defective or providing insufficient heat.

5. 5

   Monitor the sensor data for negative drift or a completely static signal.

1. 1

   Locate the NH3 sensor

   Locate the NH3 sensor, which is mounted on the SCR muffler and catalyst assembly.

2. 2

   Gain access to the sensor

   Depending on the specific machine (e.g., Farmall 130A), you may need to remove the SCR muffler and catalyst upper heat shield to gain access. In some configurations, removing the downstream temperature sensor or exhaust outlet pipe clamps may also be necessary for clearance.

3. 3

   Disconnect wiring

   Disconnect the wiring harness from the NH3 sensor.

4. 4

   Remove sensor

   Remove the faulty Ammonia (NH3) sensor.

5. 5

   Install new sensor

   Install the new NH3 sensor and reconnect the wiring harness.

6. 6

   Reinstall components

   Reinstall any heat shields or exhaust components removed during disassembly.

7. 7

   Perform verification test

   Connect the Case IH Electronic Service Tool (EST) and perform the "SCR Fault Repair Verification Test". Simply replacing the part will not clear the power derate.

8. 8

   Reset engine restart counter

   Use the EST to navigate to the configure menu and perform the "Engine Restart Counter Reset / Unlock Inducement" configuration before returning the machine to service.