New Holland ENG 3171 – Engine Control Unit (ECU): Diesel Particulate Filter (DPF) Outlet Pressure #1: P1 is Out of Voltage - Low

This code indicates an electrical fault where the signal voltage from the DPF Outlet Pressure Sensor has dropped below the minimum acceptable threshold. Because the voltage is out of range on the low side, the system cannot accurately measure the exhaust pressure exiting the DPF. This is typically an electrical circuit issue (such as a short to ground, an open circuit, or a dead sensor) rather than a physical exhaust blockage.

• L220
• L223
• L225
• L230
• L234
• C232
• C238
• SR175
• Case SR130
• Case SR160

1. 1

   Inspect the wiring harness leading to the DPF Outlet Pressure Sensor for melted wires, chafing, or physical damage near the hot exhaust.

2. 2

   Disconnect the sensor and inspect the pins for corrosion, moisture ingress, or bent terminals.

3. 3

   Turn the key to the ON position (engine off) and verify that the sensor connector is receiving the correct 5V reference voltage and has a solid ground from the ECU.

4. 4

   Check the signal wire for continuity between the sensor connector and the ECU harness, and test the signal wire for a short to ground.

5. 5

   If the wiring is intact, the reference voltage is present, and there is no short to ground in the harness, the sensor itself has failed internally and must be replaced.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the negative battery cable to prevent electrical shorts. Ensure the exhaust system has completely cooled down, as the DPF assembly operates at extremely high temperatures.

2. 2

   Locate the Sensor

   Locate the DPF Outlet Pressure Sensor on the exhaust aftertreatment system, positioned downstream of the Diesel Particulate Filter.

3. 3

   Disconnect Electronics

   Carefully depress the locking tab and remove the electrical harness connector from the sensor.

4. 4

   Remove the Sensor

   Unbolt or unscrew the pressure sensor from its mounting bracket or exhaust pressure tube. Use a wrench to hold the pressure tube fitting steady so you do not twist or damage the metal lines leading into the exhaust pipe.

5. 5

   Install the New Sensor

   Thread the new DPF Outlet Pressure Sensor into place and tighten it to the OEM torque specification.

6. 6

   Reconnect

   Plug the electrical harness back into the sensor until it clicks securely. Reconnect the battery.

7. 7

   Clear Codes and Test

   Connect an electronic service tool to the machine's diagnostic port and clear the ENG 3171 fault code. Start the engine and verify that the code does not return. If required by the service tool, perform a stationary DPF regeneration or an Air System Service Test to ensure the ECU is reading the outlet pressure correctly.