Sumitomo SH220LC-6 Fault Code 7420: Complete Diagnostic Guide

What is Sumitomo SH220LC-6 Fault Code 7420?

Fault Code 7420 on the Sumitomo SH220LC-6 excavator indicates a hydraulic pump pressure sensor circuit malfunction or abnormal signal voltage detected by the machine's Electronic Control Module (ECM). This diagnostic trouble code specifically relates to the main hydraulic pump's pressure monitoring system, which is critical for load-sensing hydraulic performance.

The pressure sensor continuously monitors hydraulic system pressure and sends voltage signals to the ECM to optimize pump output and prevent system overload. When the ECM detects voltage readings outside the normal range (typically 0.5-4.5V), it triggers Code 7420. This is particularly critical on the SH220LC-6 because the load-sensing hydraulic system relies on accurate pressure data to modulate pump displacement and maintain efficient operation across varying loads.

Common Symptoms

When Code 7420 is active, operators typically experience:

• Reduced hydraulic power or sluggish boom/arm/bucket response during operation
• Intermittent or constant warning lamp illumination on the instrument cluster
• Erratic engine RPM fluctuations when hydraulic functions are engaged
• Loss of fine control during precision digging or grading operations
• Automatic engine derate or power limitation in severe cases to protect the hydraulic system

Potential Causes

The most common technical failures triggering Code 7420 on used SH220LC-6 excavators include:

• Hydraulic pump pressure sensor failure due to internal diaphragm rupture or contamination from hydraulic fluid breakdown
• Damaged wiring harness near the main pump mounting area, where vibration and heat cause insulation deterioration
• Corroded or loose connector pins at the sensor plug, especially on machines operating in wet or corrosive environments
• ECM internal circuit degradation, though less common, particularly in high-hour machines (8,000+ hours)
• Hydraulic oil contamination causing sensor port blockage or erratic pressure readings
• Ground circuit failure between the sensor and chassis, common at worn mounting brackets

How to Troubleshoot and Fix Code 7420

Step 1: Visual Inspection Begin by inspecting the hydraulic pump pressure sensor located on the main pump assembly. Check for physical damage, hydraulic oil leakage around the sensor body, and examine the wiring harness for abrasion points where it contacts the pump housing or frame rails—a known wear point on used SH220LC-6 models.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. The typical range should be 250-350 ohms at room temperature. Next, check the supply voltage at the harness connector with the ignition on—it should read approximately 5.0V. Measure ground circuit continuity to ensure less than 1 ohm resistance to chassis ground.

Step 3: Signal Voltage Verification Reconnect the sensor and backprobe the signal wire while starting the engine. Monitor voltage with the engine at idle and under load. Normal operation shows 0.5-1.2V at idle, increasing proportionally with hydraulic demand. Erratic or out-of-range readings confirm sensor replacement is necessary.

Step 4: Connector and Harness Repair For used excavators, thoroughly clean all connector pins with electrical contact cleaner and inspect for corrosion (green discoloration). Apply dielectric grease to prevent future moisture intrusion. If harness damage is found, repair using proper gauge wire and heat-shrink terminals rather than replacing entire harnesses unnecessarily.

Step 5: Sensor Replacement and Calibration If testing confirms sensor failure, replace with a genuine Sumitomo pressure sensor (Part# varies by build date—consult serial number). After installation, clear codes using diagnostic software compatible with Sumitomo systems and perform a pressure calibration procedure per the service manual specifications.

---

Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Sumitomo SH220LC-6 service manual and consider professional assistance for complex electrical diagnostics or if unfamiliar with high-pressure hydraulic systems.