XCMG QSX15 Fault Code 157-4: Complete Diagnostic Guide

What is XCMG QSX15 Fault Code 157-4?

Fault Code 157-4 indicates a moderately severe condition in the Injector Cylinder #4 Circuit, specifically detecting a current below normal or shorted to ground. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects abnormal electrical resistance or a short circuit in the fuel injector wiring or solenoid for cylinder #4 on the Cummins QSX15 engine powering your XCMG excavator.

This code is critical because the QSX15's common rail fuel injection system relies on precise electronic control of each injector. When cylinder #4's injector circuit malfunctions, the ECM cannot properly meter fuel delivery, leading to rough running, power loss, and potential damage to the catalytic aftertreatment system due to incomplete combustion. In used excavators, this fault often stems from harness degradation rather than injector failure itself.

Common Symptoms

• Check Engine Light (CEL) illuminated on the instrument cluster with possible amber warning indicator
• Rough idle or misfiring sensation, particularly noticeable at low engine RPM during warm-up
• Reduced engine power and sluggish hydraulic response during digging or lifting operations
• Black or white smoke from the exhaust stack, indicating improper fuel combustion
• Increased fuel consumption as the ECM attempts to compensate for the cylinder #4 misfire

Potential Causes

The most common technical causes for Code 157-4 on used XCMG QSX15 excavators include:

• Damaged or chafed injector harness at cylinder #4, especially where the wiring passes near engine mounts or vibrates against metal surfaces
• Corroded or moisture-contaminated electrical connector at the #4 fuel injector (common in machines operating in wet or marine environments)
• Failed injector solenoid coil within the #4 fuel injector assembly showing abnormal resistance
• Shorted wiring to ground due to harness insulation breakdown from heat exposure near the exhaust manifold
• ECM internal driver circuit failure (less common but possible in high-hour machines)
• Loose or corroded ground connections affecting the entire injector circuit reference voltage

How to Troubleshoot and Fix Code 157-4

Step 1: Visual Inspection Begin with the engine off and cooled. Locate the #4 fuel injector on the driver's side of the engine block. Carefully inspect the injector harness connector for corrosion, bent pins, or moisture intrusion. On used excavators, pay special attention to harness routing—look for signs of rubbing, melted insulation, or oil contamination that can degrade wire integrity.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the injector connector and measure resistance across the injector solenoid terminals. Specification for QSX15 injectors is typically 0.3-0.9 ohms at room temperature. Next, check for continuity between each injector terminal and ground—any reading below 10k ohms indicates a short to ground condition. Also verify harness integrity by back-probing the ECM connector (typically requiring Cummins INSITE diagnostic software to identify pin locations).

Step 3: Component Replacement or Repair If resistance values are out of specification, replace the #4 fuel injector assembly with a genuine Cummins or OEM-equivalent part. If wiring shows damage, repair the injector harness using proper gauge wire and heat-shrink connections—never use electrical tape in high-temperature environments. For used machines with multiple harness wear points, consider replacing the entire engine harness to prevent recurring codes. After repairs, clear codes with INSITE software and perform a cylinder contribution test to verify proper operation.

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Disclaimer: This guide provides general diagnostic information for Code 157-4. Always consult the official XCMG service manual and Cummins troubleshooting procedures for your specific machine serial number. If you lack experience with high-pressure fuel systems or electronic diagnostics, seek assistance from a certified Cummins or XCMG technician to avoid injury or equipment damage.