Case IH 3639 – Engine Control Unit (ECU): NOx Sensor drift test

The NOx sensor's readings have drifted outside of the acceptable calibration range or plausibility limits during the system's self-test.

• Magnum (180 to 370)
• Steiger/Quadtrac (350 to 600)
• Puma (130 to 230)
• Maxxum (110 to 140)
• Farmall series
• 5130
• 6130
• 7130
• 7230
• 8230
• 9230
• Farmlift series (632, 635, 735, 742, 935)

1. 1

   Turn the key switch OFF and visually inspect connections between the ECU and the NOx Module for tightness, security, and corrosion

2. 2

   Verify that the connector locks on the ECU and DCU are not broken and securely hold the connectors in a locked position

3. 3

   Measure the resistance through the SCR CAN bus harness (should be less than 10 Ω)

4. 4

   Use the CNH Electronic Service Tool (EST) to check the CAN network for active communication

1. 1

   Power Down

   Turn the ignition key switch OFF.

2. 2

   Inspect Wiring

   Trace the SCR CAN bus harness. If damaged wiring is found, repair the damaged wiring and retest the circuit.

3. 3

   Isolate the Circuit

   Disconnect all components connected to the SCR CAN Bus.

4. 4

   Jumper Test

   Fabricate a 20 cm (8 in) jumper wire. Connect the jumper between the ECU SCR CAN High and SCR CAN Low pins.

5. 5

   Measure Resistance

   Measure the resistance through the SCR CAN bus circuit. If the resistance is higher than 10 Ω, temporarily replace the SCR CAN bus wires and retest. Repair or replace the harness as required.

6. 6

   Replace Sensor

   If the wiring, connectors, and CAN bus resistance are all within specification, the NOx sensor itself has failed the drift test and must be replaced.

7. 7

   Clear Codes

   After fitting the new NOx sensor, use the EST to clear the error codes. The system may require a run cycle to validate the repair.