Sumitomo SH300-6 Fault Code 91: Complete Diagnostic Guide

What is Sumitomo SH300-6 Fault Code 91?

Fault Code 91 on the Sumitomo SH300-6 excavator indicates a Pump Solenoid Valve Circuit malfunction, specifically related to the main hydraulic pump's electronic control system. This code triggers when the Electronic Control Module (ECM) detects abnormal voltage or current flow in the pump control solenoid circuit, which regulates hydraulic flow and pressure.

This fault is critical because the pump solenoid valve directly controls the swash plate angle of the main hydraulic pump, affecting excavator performance, fuel efficiency, and responsiveness. On used machines, this code often signals deteriorating electrical connections or component wear that can lead to significant productivity loss if left unaddressed.

Common Symptoms

When Code 91 is active on your SH300-6, operators typically experience:

• Erratic hydraulic response with inconsistent boom, arm, or bucket speed
• Loss of power during digging operations or reduced breakout force
• Warning light illumination on the instrument panel (typically yellow or amber)
• Engine RPM fluctuations when operating multiple hydraulic functions simultaneously
• Intermittent fault that appears during cold starts or under heavy load conditions

Potential Causes

The most common technical reasons for Code 91 on used SH300-6 excavators include:

• Damaged wiring harness near the main pump assembly where vibration causes conductor breakage or insulation wear
• Corroded connector pins at the pump solenoid valve plug (common in machines operating in wet/muddy environments)
• Failed pump solenoid valve due to internal coil breakdown or mechanical sticking
• ECM power supply issues affecting the 12V reference voltage to the solenoid circuit
• Grounding problems at chassis ground points, particularly after frame repairs or modifications

How to Troubleshoot and Fix Code 91

Step 1: Visual Inspection Begin by inspecting the wiring harness running from the ECM to the main hydraulic pump. On used excavators, check for harness rubbing against the pump housing, cracked insulation, or corroded connectors. Clean all connector pins with electrical contact cleaner and verify proper seating.

Step 2: Electrical Testing Using a digital multimeter, check the solenoid coil resistance (typically 8-15 ohms for Sumitomo pumps). With ignition ON, measure voltage at the solenoid connector—you should see approximately 12V. Check for continuity to ground and verify no short circuits exist.

Step 3: Component Testing If electrical values are correct, perform a dynamic test using Sumitomo's diagnostic software or a compatible scan tool. Monitor solenoid PWM duty cycle during operation. Replace the pump solenoid valve if resistance is out of specification or if the valve fails to respond to commanded signals.

Step 4: Verify Repair After repairs, clear the fault code, operate all hydraulic functions under load, and re-scan for codes. For used machinery, perform this verification during different temperature conditions to ensure intermittent connection issues are resolved.

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