Case IH 3771 – Engine ECU: Oxidation Catalyst: Up and down stream temperature sensors in Oxidation catalysts exchanged

The system has detected that the temperature readings for the Diesel Oxidation Catalyst (DOC) are inverted. This typically means the upstream and downstream exhaust gas temperature (EGT) sensors or their electrical wiring connectors have been physically swapped or plugged into the wrong ports during assembly or previous service.

• Magnum 290
• Maxxum 120
• Maxxum 125
• Maxxum 130
• Maxxum 140
• Puma 140
• Puma 210
• Farmall 100C
• Farmall 105A
• Farmall 105C
• Farmall 105U
• Farmall 110A
• Farmall 110C
• Farmall 110U
• Farmall 115A
• Farmall 115C
• Farmall 115U
• Farmall 120U
• SR220
• SR250
• SV250
• SV300
• TR320
• TV380

1. 1

   Visually inspect the Diesel Oxidation Catalyst (DOC) chamber to identify the upstream (entering) and downstream (exiting) temperature sensors

2. 2

   Trace the wiring from both sensors to the engine wiring harness to verify that the upstream sensor is plugged into the upstream connector and the downstream sensor is plugged into the downstream connector

3. 3

   Check for previous service on the exhaust system, DOC, or sensors, as this code is typically triggered by human error during reassembly

1. 1

   Power Down

   Turn off the machine and allow the exhaust system to cool completely to avoid burns, as the DOC operates at extremely high temperatures.

2. 2

   Correct the Sensor Orientation

   If the electrical connectors are swapped, simply disconnect both sensors and plug them into their correct respective harness connectors. If the physical sensors were threaded into the wrong bungs (and have different part numbers/lengths), remove them using a 17mm wrench (standard for M14 x 1.5 sensors) and reinstall them in the correct upstream/downstream positions.

3. 3

   Clear the Code

   Use the Case IH Electronic Service Tool (EST) to clear the inactive fault code from the Engine ECU, or run the machine to allow the ECU to verify the temperature plausibility and self-clear the active status.