Case IH 3840 – Engine Control Unit (ECU): Temperature Sensor Circuit (T2) Downstream Oxicat - High Error

The Engine Control Unit has detected that the signal voltage from the temperature sensor located downstream of the Diesel Oxidation Catalyst (DOC / Oxicat) and upstream of the DPF is exceeding the maximum plausible range (SRC High). This condition typically points to a short circuit to a high voltage source, an open circuit, or an internally failed sensor.

• skid steer
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• Farmall
• Magnum
• Steiger

1. 1

   Visually inspect the T2 temperature sensor, engine main harness, and connectors for frayed wires, pulled terminals, or physical damage.

2. 2

   Verify sensor placement to ensure the upstream (T1) and downstream (T2) Oxicat temperature sensors have not been accidentally interchanged.

3. 3

   Check the exhaust gas piping for physical damage, cracks, or blockages that could cause abnormal temperature readings.

4. 4

   Test the sensor circuit with a multimeter to rule out a short to battery voltage or an open load in the wiring harness.

1. 1

   Locate the Sensor

   Identify the T2 Exhaust Gas Temperature Sensor located on the exhaust path, specifically downstream of the DOC (Oxicat) and before the DPF.

2. 2

   Inspect and Repair Wiring

   Disconnect the sensor. If the diagnostic checks revealed damaged wiring or a short to ground/power in the harness, repair the damaged sections or replace the connector pigtail.

3. 3

   Replace the Sensor

   If the wiring harness tests perfectly but the ECU still reports a high voltage error, the sensor itself has failed internally. Remove the old sensor and install a new OEM replacement.

4. 4

   Reconnect and Clear

   Reconnect all harnesses securely. Use the Case IH Electronic Service Tool (EST) or EASy tool to clear the inactive fault codes from the Engine ECU.

5. 5

   Verify Repair

   Start the engine and allow it to reach operating temperature. Verify that fault code 3840 does not return and that the exhaust temperature readings are within normal parameters.