Case IH F-4765-14 - ECU – Engine Control Unit (ECU): DOC upstream temperature sensor signal drift at cold start

The Engine Control Unit (ECU) has detected a plausibility error during a cold start: the temperature reading from the sensor located upstream of the Diesel Oxidation Catalyst (DOC) deviates significantly from the readings of other engine/ambient temperature sensors. This is often an environmental anomaly (such as exposure to direct sunlight or a warm air stream) rather than a hard part failure.

• MAGNUM AFS Connect
• Case IH Steiger Tractors (535, 580)
• Case IH Magnum Tractors (180, 200, 220, 240, 310)
• Case IH Maxxum Tractors (115, 125, 135, 145, 150)
• Case IH Farmall Tractors
• Case IH Axial-Flow Combines (240 series, 7120, 8120)
• Case IH Austoft Harvesters (9900)

1. 1

   Environmental Plausibility Check: Determine the machine's parking conditions prior to the cold start. If the exhaust was exposed to direct sunlight after a cold night, or parked near an external heat source, no action is needed. Clear the code and monitor.

2. 2

   Sensor Mounting Check: Verify that the temperature sensors upstream and downstream of the DOC have not been installed incorrectly or swapped during previous exhaust work.

3. 3

   Wiring and Connector Inspection: Check the sensor's wiring harness and connector (often designated as C189 or X189) for continuity, proper pin contact, and corrosion.

1. 1

   Turn off the machine and engage the master battery disconnect switch

   Cut power to the ECU.

2. 2

   Locate the DOC upstream temperature sensor

   Find the sensor on the exhaust aftertreatment assembly (positioned before the Diesel Oxidation Catalyst).

3. 3

   Disconnect the electrical connector

   Disconnect the 2-cavity electrical connector (C189 / X189) from the sensor.

4. 4

   Remove the temperature sensor

   Carefully unthread and remove the temperature sensor from the exhaust system bung (penetrating oil may be required if carbon/heat has seized the threads).

5. 5

   Install the new DOC upstream temperature sensor

   Tighten it to the OEM torque specification.

6. 6

   Reconnect the electrical connector

   Ensure the weather seal clicks into place.

7. 7

   Verify sensor reading and clear fault code

   Restore battery power, turn the key on, and use a diagnostic service tool to verify the new sensor is reading a plausible ambient temperature matching the other engine sensors before starting the engine. Clear the F-4765-14 fault code.