What is XCMG XE750D Fault Code 175-4 SPN175 FMI4?

Fault Code 175-4 (SPN 175 FMI 4) indicates a voltage problem below normal or shorted to ground in the engine oil temperature sensor circuit. This code is part of the J1939 diagnostic protocol used in modern diesel engines and specifically points to the Engine Oil Temperature (EOT) sensor sending incorrect low voltage signals to the Engine Control Module (ECM).

For the XCMG XE750D excavator, this fault directly impacts the ECM's ability to manage engine protection strategies, fuel injection timing, and cooling system operation. The engine oil temperature data is critical for preventing catastrophic engine damage, especially during cold starts and high-load operations common in heavy excavation work.

Common Symptoms

When this fault code is active on your XE750D, you may experience:

• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Engine derate mode engaging, limiting maximum RPM and hydraulic power output to protect the engine
• Difficulty starting in cold weather, as the ECM cannot properly adjust cold-start fuel enrichment
• Abnormal cooling fan operation, running constantly at high speed or not engaging when needed
• Stored fault codes that prevent the machine from passing emissions compliance checks

Potential Causes

The most common technical causes for Code 175-4 on used XCMG excavators include:

• Damaged or corroded wiring harness between the oil temperature sensor and ECM, particularly at connector pins exposed to engine heat and vibration
• Failed engine oil temperature sensor due to internal short circuit or thermal degradation (common after 5,000+ operating hours)
• Shorted sensor wiring to chassis ground, often caused by harness rubbing against engine block or frame rails
• Corroded connector terminals at the sensor or ECM, allowing moisture intrusion in the engine compartment
• ECM internal fault (rare, but possible in high-hour machines with electrical system history)

How to Troubleshoot and Fix Code 175-4

Step 1: Visual Inspection Begin by locating the engine oil temperature sensor (typically mounted in the engine oil pan or oil filter housing on XCMG diesel engines). Inspect the sensor connector and wiring harness for obvious damage, oil contamination, corrosion, or abraded insulation. On used excavators, pay special attention to harness routing near hot exhaust components or sharp metal edges.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter (DMM) to measure resistance across the sensor terminals. A functional oil temperature sensor typically shows 200-3,000 ohms depending on oil temperature (consult XCMG service manual for exact specifications). Also check for continuity to ground—there should be infinite resistance between each sensor terminal and chassis ground.

Step 3: Wiring Harness Check With the sensor disconnected, measure voltage at the harness connector (ECM side) with ignition on. You should see approximately 5 volts supply voltage from the ECM. Check harness continuity from sensor connector back to ECM pins, and verify no shorts to ground along the entire wire run.

Step 4: Component Replacement If the sensor tests faulty, replace with an OEM or quality aftermarket oil temperature sensor. If wiring shows damage, repair using weatherproof heat-shrink connectors and reroute away from heat sources. After repairs, clear codes using XCMG diagnostic software or a compatible J1939 scan tool and perform a test run under load.

Used Equipment Consideration: Before replacing expensive components, thoroughly clean all connector pins with electrical contact cleaner and apply dielectric grease. Many fault codes on high-hour machines resolve with proper connector maintenance.

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Disclaimer: This guide provides general diagnostic information. Always consult the official XCMG XE750D service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic equipment.