Case IH 3801 – ENGINE ECU: Turbine upstream pressure sensor: SRC High for Turbine upstream pressure sensor.

The signal voltage from the turbine upstream pressure sensor (exhaust manifold pressure sensor or exhaust back pressure sensor) is reading above the maximum allowable limit, indicating an electrical issue such as a short circuit to an external power source (short to battery) or a completely failed sensor.

• Farmall
• skid steer
• tractors
• combines
• heavy equipment
• wheel loaders

1. 1

   Inspect the wiring harness leading to the turbine upstream pressure sensor for chafing, melting, or exposed wires that could cause a short to voltage.

2. 2

   Disconnect the sensor and inspect the pins for corrosion, moisture, or damage.

3. 3

   Using a multimeter, check the sensor's signal wire for a short circuit to the battery/power supply.

4. 4

   With the engine off and the key on, use a diagnostic scan tool to read the sensor's live data. It should roughly match atmospheric pressure. If it is pegged at its maximum value (e.g., 5V), the sensor is internally shorted or the wiring is compromised.

1. 1

   Power Down

   Turn off the engine and turn the key start switch to the OFF position.

2. 2

   Locate the Sensor

   Find the turbine upstream pressure sensor, which is typically plumbed into the exhaust manifold or the exhaust piping just before the turbocharger.

3. 3

   Disconnect

   Unplug the machine harness connector from the sensor.

4. 4

   Wiring Repair (If Applicable)

   If your diagnostic tests revealed a short to power in the harness, trace the wiring back to the Engine ECU and repair the damaged section of the harness.

5. 5

   Replace the Sensor

   If the wiring tests good, the sensor itself has failed internally. Unthread the old sensor from the exhaust pressure tube. Install the new sensor and tighten it to OEM specifications.

6. 6

   Reconnect and Clear

   Plug the harness connector back into the new sensor. Turn the key on, connect your diagnostic tool, and clear the active/inactive 3801 fault code.

7. 7

   Verify

   Start the engine and verify that the code does not return and that the sensor reads appropriate exhaust back pressure under load.