What is Hyundai R335LC-9T Fault Code 627-12?

Fault Code 627-12 on the Hyundai R335LC-9T excavator indicates a "Pump Control Solenoid Valve #1 - Current Below Normal or Shorted to Ground." This diagnostic trouble code (DTC) is triggered when the Electronic Control Unit (ECU) detects abnormally low current flow through the main hydraulic pump's control solenoid valve circuit, or when the circuit has a short to ground.

This code specifically affects the proportional solenoid valve that regulates the swash plate angle on the primary hydraulic pump. The solenoid controls pump output by adjusting displacement based on load demand. When this circuit fails, the excavator's hydraulic system cannot properly modulate pump flow, critically impacting performance and fuel efficiency. For the R335LC-9T's advanced load-sensing hydraulic system, this fault can severely compromise operational capability.

Common Symptoms

• Reduced hydraulic power across all functions (boom, arm, swing, and travel)
• Service warning light illuminated on the instrument cluster with fault code displayed
• Engine auto-derating or rpm limitation to protect the hydraulic system
• Erratic hydraulic response or inconsistent implement speeds during operation
• Increased fuel consumption due to improper pump regulation and efficiency loss

Potential Causes

The most common technical causes for Code 627-12 on used R335LC-9T excavators include:

• Failed pump control solenoid valve due to internal coil winding damage or mechanical seizure
• Damaged wiring harness between the ECU and solenoid, particularly at known rub points near the pump mounting area and along the main boom pivot
• Corroded or loose electrical connectors at the solenoid valve or ECU interface (common in machines with high hour counts)
• Short to ground in the solenoid circuit wiring, often caused by harness chafing against frame components
• ECU internal fault (less common) affecting the solenoid driver circuit output
• Poor ground connections at the pump assembly or main chassis ground points

How to Troubleshoot and Fix Code 627-12

Step 1: Visual Inspection and Connector Check Begin by inspecting the pump control solenoid valve connector located on the main hydraulic pump assembly. Disconnect the connector and examine both the pin terminals and socket contacts for corrosion, bent pins, or moisture intrusion. On used excavators, this connector frequently accumulates hydraulic fluid contamination. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: Solenoid Resistance Test Using a digital multimeter, measure the resistance across the solenoid valve terminals. Typical specification for the R335LC-9T pump solenoid is 3-7 ohms at 20°C. Reading below 2 ohms indicates a short within the coil; reading infinite resistance confirms an open circuit. Also test for short to ground by measuring resistance between each solenoid terminal and pump body (should read infinite/open circuit).

Step 3: Wiring Harness Continuity and Ground Test Trace the solenoid harness from the pump back to the ECU connector, paying special attention to areas where the harness passes near moving components or sharp edges. Check for continuity from ECU connector pins to solenoid connector (should be less than 1 ohm). Test for shorts to ground along the entire harness length—resistance to chassis ground should be infinite.

Step 4: Voltage Supply Check With the key on and engine running, use a multimeter to verify the ECU is supplying voltage to the solenoid circuit (typically 12V PWM signal). If no voltage is present despite good wiring and solenoid, suspect an ECU driver circuit failure. For used machines, inspect all ground connections at the pump mounting bracket and main chassis ground points—clean and tighten as corrosion commonly develops over time.

Step 5: Component Replacement and Verification If the solenoid valve tests faulty, replace with a genuine Hyundai or OEM-equivalent proportional valve. After replacement, clear fault codes using Hi-SCANPro diagnostic software or equivalent Hyundai-compatible scan tool, then cycle the machine through all hydraulic functions to verify proper operation and confirm the code does not return.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the Hyundai R335LC-9T service manual for exact specifications and procedures. If unfamiliar with hydraulic systems or electrical diagnostics, seek assistance from a certified Hyundai excavator technician to prevent equipment damage or safety hazards.