What is XCMG XE750D Fault Code 1835-3 SPN1387 FMI3?

Fault Code 1835-3 (SPN 1387 FMI 3) indicates a voltage above normal or shorted high condition in the Engine Speed/Position Sensor 1 circuit. This code is triggered when the Engine Control Module (ECM) detects an abnormally high voltage reading from the primary engine speed sensor, which monitors crankshaft position and rotational speed.

The SPN 1387 specifically refers to the engine's primary speed/position sensor circuit, while FMI 3 denotes a voltage level exceeding the manufacturer's specified parameters. This sensor is critical for the XCMG XE750D's engine timing, fuel injection synchronization, and overall engine management. Without accurate speed data, the ECM cannot properly control fuel delivery, ignition timing, or emission systems, potentially leading to performance degradation or complete engine shutdown.

Common Symptoms

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Engine runs rough, experiences misfires, or exhibits irregular idle behavior
• Sudden engine derate mode activation, limiting machine power output to protect components
• Difficulty starting the engine or intermittent no-start conditions
• Loss of hydraulic power or reduced digging force due to engine performance restrictions

Potential Causes

The most common technical causes for this fault code in used XCMG XE750D excavators include:

• Damaged or frayed sensor wiring harness, particularly at flex points near the engine block where vibration and heat cause insulation breakdown
• Corroded or moisture-contaminated connector pins at the speed sensor or ECM connection points
• Failed crankshaft position sensor due to internal short circuit or heat damage
• Chafed wiring rubbing against the engine block, starter motor housing, or hydraulic lines creating intermittent short-to-power conditions
• ECM internal fault or poor grounding at the ECM mounting location
• Aftermarket sensor installation with incorrect voltage specifications

How to Troubleshoot and Fix Code 1835-3 SPN1387 FMI3

Step 1: Visual Inspection Begin by thoroughly inspecting the crankshaft position sensor wiring harness from the sensor to the ECM connector. On used excavators, check for visible wire damage, particularly where the harness passes near hot exhaust components or moving engine parts. Look for melted insulation, exposed copper wire, or evidence of previous repairs.

Step 2: Connector and Pin Examination Disconnect the speed sensor connector and inspect for corrosion, bent pins, or moisture intrusion. Clean connections with electrical contact cleaner and examine the sensor terminals for greenish corrosion typical in older machines. Check the ECM harness connector similarly, as corrosion here creates high resistance that mimics sensor failure.

Step 3: Electrical Testing Using a digital multimeter, measure voltage at the sensor connector with the ignition on, engine off. Compare readings against XCMG specifications (typically 5V reference voltage). With the sensor disconnected, check for short-to-power by measuring voltage on the signal wire—any reading above 0.5V indicates a wiring short. Test sensor resistance (usually 200-1000 ohms) and compare to factory specifications.

Step 4: Sensor and Wiring Replacement If electrical tests confirm high voltage, trace and repair the harness short before replacing components. For used excavators, replace the entire harness section rather than splicing, as aged insulation often fails at multiple points. Install a new OEM-quality crankshaft position sensor and ensure proper air gap clearance (typically 0.5-1.5mm). Secure all wiring away from heat sources and moving parts using proper cable ties and protective loom.

Step 5: Clear Codes and Verify After repairs, clear fault codes using XCMG diagnostic software or a compatible scan tool. Run the engine through multiple operating cycles and monitor for code recurrence. Perform a road test under load to ensure the issue is fully resolved.

---

Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the XCMG XE750D service manual and qualified diesel technicians for your specific machine. Improper repairs can cause equipment damage or safety hazards.