Case IH 19551 – Engine Control Module (ECM) or Dosing Control Unit (DCU): Short circuit error for the NOx signal

The control module has detected a short circuit in the electrical signal circuit of the Nitrogen Oxide (NOx) sensor. Because of this short circuit, the sensor cannot transmit reliable exhaust emission data to the computer, which will likely trigger an SCR (Selective Catalytic Reduction) system failure warning or an engine derate.

• Tier 4b
• Magnum (180, 190, 210, 225, 235, 260, 290, 315, 340, 370)
• Steiger & Quadtrac (350, 400, 450, 500, 550, 600)
• Puma (150, 165)
• Farmall (110A, 120A, 130A, 140A)
• Axial-Flow 5130, 6130, 7130, 7230, 8230, 9230, 5140, 6140, 7140, 7240, 8240, 9240
• Patriot (2240, 2250, 3240, 3340, 4430, 4440)
• Titan (3030, 3040, 3530, 3540, 4030, 4040, 4530, 4540)
• Case Construction Loaders 521F, 621F, 721F, 821F, 921F, 1021F, 1121F

1. 1

   Inspect the NOx sensor wiring harness for chafing, melting from exhaust heat, or physical damage.

2. 2

   Disconnect the NOx sensor and inspect the connector pins for moisture, corrosion, or pushed-out pins.

3. 3

   Using a multimeter, check the sensor's signal wire for a short to ground or a short to voltage. Verify that the sensor is receiving proper power and ground from the ECM/DCU.

1. 1

   Turn off the machine and disconnect the battery

   Turn off the machine and disconnect the battery to prevent electrical spikes.

2. 2

   Locate the faulty NOx sensor

   Locate the faulty NOx sensor on the exhaust system (the specific sensor location—upstream or downstream of the catalyst—will depend on the exact machine configuration).

3. 3

   Disconnect the electrical connector

   Disconnect the 5-pin electrical connector for the NOx sensor.

4. 4

   Unscrew the NOx sensor

   Carefully unscrew the NOx sensor from the exhaust pipe. (Penetrating oil may be required if the sensor is seized from exhaust heat).

5. 5

   Install the new NOx sensor

   Install the new NOx sensor into the exhaust pipe. Ensure anti-seize is applied to the threads (avoid getting it on the sensor tip).

6. 6

   Route the wiring harness

   Route the wiring harness safely away from extreme heat sources and reconnect the electrical plug.

7. 7

   Reconnect the battery

   Reconnect the battery and turn on the ignition.

8. 8

   Clear the fault codes

   Use a diagnostic tool (such as the CNH Electronic Service Tool) to clear the fault codes. Note: Error cleaning is required after fitting a new NOx sensor.

9. 9

   Run the engine

   Run the engine to allow the SCR system to heat up and verify that the code does not return.