What is XCMG XE750D Fault Code 174-4 SPN174 FMI4?

Fault Code 174-4 (SPN 174, FMI 4) indicates a voltage below normal or shorted to ground condition in the fuel injection actuation pressure circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects that the fuel rail pressure sensor is reading voltage levels significantly lower than the expected operating range, typically below 0.5 volts.

On the XCMG XE750D excavator, this code specifically targets the fuel injection actuation pressure sensor and its associated wiring harness. The sensor monitors the hydraulic pressure used to actuate the unit injectors or common rail injectors, which is critical for precise fuel delivery timing and quantity. When this circuit fails, the ECM cannot accurately control fuel injection events, directly impacting engine performance, fuel efficiency, and emissions compliance. For a machine of this size and application, maintaining proper fuel system voltage signals is essential for delivering the power needed for heavy digging and lifting operations.

Common Symptoms

• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the instrument cluster
• Engine power derate or limited throttle response, preventing the excavator from reaching full RPM
• Rough idling or unstable engine operation, particularly during cold starts
• Increased black smoke from the exhaust due to improper fuel metering
• Difficulty starting the engine, especially after the machine has been sitting idle

Potential Causes

The most common technical causes for Code 174-4 on used XCMG XE750D excavators include:

• Damaged or corroded wiring harness between the fuel pressure sensor and ECM, particularly at flex points near the engine mount or valve cover
• Failed fuel injection actuation pressure sensor due to internal circuit degradation or contamination
• Chafed wires rubbing against the engine block, frame rails, or hydraulic lines—common in high-vibration environments
• Corroded or loose connector pins at the sensor plug or ECM connection points
• Shorted sensor ground wire to chassis ground or engine block
• Water intrusion into the sensor connector from damaged seals or improper maintenance
• ECM internal fault (less common, but possible in machines with high operating hours)

How to Troubleshoot and Fix Code 174-4 SPN174 FMI4

Step 1: Visual Inspection of Harness and Connections

Begin by thoroughly inspecting the fuel injection pressure sensor wiring harness from the sensor to the ECM. On used excavators, focus on areas where the harness passes near moving components, sharp edges, or heat sources. Look for abraded insulation, pinched wires, or signs of previous repairs. Check all connector pins for corrosion, bent pins, or moisture intrusion. Clean connectors with electrical contact cleaner and ensure they click firmly into place.

Step 2: Sensor and Circuit Voltage Testing

Using a digital multimeter (DMM), perform voltage checks at the sensor connector with the key in the "ON" position (engine off). The 5-volt reference supply from the ECM should measure between 4.5-5.5 volts. Check the sensor ground circuit for continuity to chassis ground (should read less than 0.5 ohms resistance). With the sensor disconnected, measure resistance between the signal wire and ground—infinite resistance indicates no short, while low resistance (under 100 ohms) confirms a short circuit requiring harness repair.

Step 3: Sensor Replacement and ECM Verification

If wiring tests pass, replace the fuel injection actuation pressure sensor with an OEM or high-quality aftermarket unit. After installation, clear fault codes using XCMG diagnostic software or a compatible J1939 diagnostic tool. Perform a road test under load conditions. If the code returns immediately, suspect ECM internal issues or incorrect sensor calibration values. For used machines with over 8,000 operating hours, consider having the ECM professionally tested or reflashed with updated software.

Disclaimer: This guide provides general diagnostic information. Always consult the XCMG XE750D service manual and consider professional assistance from a certified heavy equipment technician for complex electrical diagnostics or if you're unfamiliar with high-pressure fuel systems.