Case IH F-3242-14 - ECU – Engine Control Unit (ECU): SCR downstream temperature sensor signal drift at cold start

During a cold start, the Engine Control Unit (ECU) compares the reading from the SCR (Selective Catalytic Reduction) downstream temperature sensor to a calculated "normal" ambient temperature. If the sensor's reading deviates significantly from the expected ambient temperature, the ECU detects a signal drift and logs this fault.

• MAGNUM AFS Connect
• Case IH Austoft 9900 Sugarcane Harvesters
• Case IH Magnum Series (e.g., 225, 235-340)
• Case IH Maxxum Series (115, 125, 135, 145, 150)
• Case IH Axial-Flow Combines (e.g., 240 Series, AFX 8250)
• Case IH Farmall Series

1. 1

   Check for environmental false triggers, such as sudden exposure to intense morning sunshine or a warm air stream after a cold night, which can cause the sensor to read higher than the calculated ambient temperature.

2. 2

   Inspect the sensor's wiring harness and connectors for high resistance, loose contacts, or corrosion.

3. 3

   Verify battery and alternator health, as low voltage or wiring defects can cause sensor signal drift.

4. 4

   Use the Case IH Electronic Service Tool (EST) to check for other Exhaust Gas Temperature (EGT) sensor codes.

1. 1

   Verify code and prepare machine

   Connect the EST diagnostic laptop to verify the code and ensure the machine is keyed off and the exhaust system has cooled down.

2. 2

   Locate sensor

   Locate the SCR downstream temperature sensor. It is mounted on the exhaust pipe directly after the SCR muffler/catalyst assembly.

3. 3

   Disconnect harness

   Disconnect the 2-cavity electrical connector (often designated as C193) from the sensor harness.

4. 4

   Remove faulty sensor

   Carefully unthread and remove the faulty SCR downstream temperature sensor from the exhaust pipe.

5. 5

   Install new sensor

   Install the new temperature sensor into the exhaust bung and tighten to OEM specifications.

6. 6

   Reconnect harness

   Reconnect the electrical harness.

7. 7

   Clear fault codes

   Connect the EST laptop to clear the fault codes. Note: If the tractor entered an SCR system failure "limp home" mode, key cycles will not clear the red stop sign; an EST laptop reset is mandatory to restore full power.