Yanmar General Excavator Fault Code P1664: Complete Diagnostic Guide

What is Yanmar General Fault Code P1664?

Fault Code P1664 indicates a malfunction in the Fuel Rail Pressure Relief Valve Control Circuit, specifically detecting an abnormal voltage or current signal between the Engine Control Module (ECM) and the pressure relief valve solenoid. This code triggers when the ECM detects an electrical irregularity—typically an open circuit, short to ground, or short to power—in the control wiring or the relief valve solenoid itself.

The fuel rail pressure relief valve plays a critical role in Yanmar diesel engines by regulating excessive fuel pressure within the common rail system. When this circuit malfunctions, the ECM cannot properly control fuel system pressure, which directly impacts engine performance, fuel efficiency, and emission compliance. For used excavators, this code often signals age-related electrical degradation rather than mechanical fuel system failure.

Common Symptoms

When P1664 is active on your Yanmar excavator, operators typically experience:

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the dashboard
• Engine derating or reduced power output, especially under heavy load conditions
• Rough idle or inconsistent engine RPM fluctuations
• Hard starting or extended cranking time, particularly during cold starts
• Black smoke from the exhaust indicating improper fuel combustion due to pressure irregularities

Potential Causes

The most common technical causes for P1664 on used Yanmar excavators include:

• Damaged or corroded wiring harness at the fuel rail pressure relief valve connector (common rub point near engine block)
• Failed pressure relief valve solenoid due to internal coil breakdown or contamination
• Connector pin corrosion from moisture intrusion at the valve or ECM connections
• Chafed wiring where harness routes near sharp metal edges or vibrating components
• ECM internal circuit failure (less common, but possible in high-hour machines)
• Poor ground connections at engine block grounding points

How to Troubleshoot and Fix Code P1664

Step 1: Visual Inspection Begin by thoroughly inspecting the wiring harness from the ECM to the fuel rail pressure relief valve. On used excavators, check for harness wear where it passes over the engine block or near moving components. Look for abraded insulation, crushed wires, or oil-soaked connectors that indicate deterioration.

Step 2: Connector and Pin Testing Disconnect the pressure relief valve connector and inspect for corrosion, bent pins, or moisture. Clean contacts with electrical contact cleaner. Using a digital multimeter, check for continuity between the valve connector and ECM pins (consult Yanmar wiring diagrams for specific pin locations). Resistance should typically read below 5 ohms for good connections.

Step 3: Solenoid Resistance Check Measure the solenoid coil resistance at the pressure relief valve connector. Yanmar specifications typically call for 2-8 ohms depending on model (verify with service manual). Readings outside this range indicate a failed solenoid requiring replacement.

Step 4: Voltage Supply Test With ignition on and engine off, verify the ECM is supplying proper reference voltage (typically 12V or 5V depending on system) to the valve circuit. No voltage indicates an ECM internal fault or blown fuse.

Step 5: Advanced Diagnostics Use Yanmar diagnostic software to perform active tests, commanding the relief valve open/closed while monitoring actual vs. commanded states. This identifies whether the issue is electrical control or mechanical valve sticking.

For used excavators specifically, always replace connector seals and apply dielectric grease to prevent future corrosion. Check nearby harness support clips and re-route cables away from heat sources.

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Disclaimer: This guide provides general troubleshooting information for Yanmar fault code P1664. Always consult the specific service manual for your excavator model and consider professional diagnostic assistance for complex electrical or fuel system repairs. Improper fuel system work can cause serious engine damage or safety hazards.