New Holland ENG 3840 – Engine Control Unit (ECU): Diesel Particulate Filter (DPF) Upstream Temperature Sensor: Diagnostic fault check for SRC high

The Engine Control Unit is receiving a voltage signal from the sensor that exceeds the maximum expected threshold. This condition is almost always caused by an open circuit in the sensor/wiring harness or a short circuit to a high-voltage source (such as battery voltage).

• L213
• L216
• L218
• L220
• L230
• C238
• SR175
• T5
• T6
• T7
• T8
• CX8.80
• CR7.80
• B115C

1. 1

   Visually inspect the DPF upstream temperature sensor body, pigtail wiring, and connector for physical damage, melting, or corrosion.

2. 2

   Disconnect the sensor and the Engine ECU connector to check the signal and ground wires for continuity (checking for an open circuit).

3. 3

   With the key ON (engine off), use a multimeter to perform a short-to-voltage test on the sensor signal wire to see if it is shorted to a 12V power source.

4. 4

   Measure the resistance across the pins of the temperature sensor itself. If the multimeter reads 'OL' (Open Loop) or infinite resistance, the internal thermistor has failed.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the negative battery terminal to prevent electrical spikes. Ensure the exhaust system has completely cooled down to avoid severe burns.

2. 2

   Removal

   Disconnect the electrical harness connector from the DPF upstream temperature sensor. Use a specialized sensor socket or a flare nut wrench to carefully unthread the sensor from the exhaust pipe bung. (Penetrating oil may be required if the sensor is seized).

3. 3

   Installation

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (avoid getting any on the sensor probe). Thread the new sensor into the exhaust bung and tighten to the manufacturer's specified torque (typically around 35 ft-lbs / 47 Nm, depending on the exact engine manual).

4. 4

   Reconnection

   Reconnect the sensor's electrical connector, ensuring it clicks securely into place. Reconnect the battery.

5. 5

   Verification

   Connect a diagnostic scan tool to the machine's diagnostic port. Clear the ENG 3840 fault code. Start the engine and monitor the live data for the DPF Upstream Temperature to ensure it is reading a plausible ambient/exhaust temperature. If required by the specific ECU, perform a stationary/forced DPF regeneration to verify the system is operating correctly.