Sumitomo SH80-6B Fault Code P0669-3: Complete Diagnostic Guide

What is Sumitomo SH80-6B Fault Code P0669-3?

Fault Code P0669-3 indicates a voltage irregularity or electrical fault in the Glow Plug Control Circuit for cylinder bank 3, specifically signaling that the voltage is above the normal operating range. This diagnostic trouble code (DTC) is part of the OBD-II standard emissions control system that monitors the diesel engine's cold-start aid system.

In the Sumitomo SH80-6B excavator's diesel engine, the glow plug control module regulates voltage to the glow plugs, which preheat combustion chambers for reliable starting in cold conditions. When the Engine Control Module (ECM) detects voltage exceeding manufacturer specifications in this circuit, it triggers P0669-3. This is critical because improper glow plug operation can lead to hard starting, increased white smoke during cold starts, and incomplete combustion that accelerates engine wear.

Common Symptoms

Operators may experience the following issues when Code P0669-3 is active:

• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the instrument panel
• Difficult cold starts or extended cranking time, especially in temperatures below 40°F (4°C)
• Excessive white or gray smoke from the exhaust during initial startup
• Rough idle for the first few minutes after a cold start
• Reduced engine performance until the engine reaches normal operating temperature

Potential Causes

The most common technical causes for P0669-3 on used SH80-6B excavators include:

• Faulty glow plug control module or relay providing excessive voltage to the circuit
• Short circuit in the glow plug wiring harness, particularly at rub points near the engine block or valve cover
• Corroded or damaged connector pins at the glow plug module or ECM connections (common in machines with 5,000+ operating hours)
• Failed glow plug(s) creating resistance imbalance that the control module interprets as high voltage
• ECM software glitch or internal ECM fault causing incorrect voltage readings
• Aftermarket electrical modifications or jump-start damage affecting circuit integrity

How to Troubleshoot and Fix Code P0669-3

Step 1: Visual Inspection and Code Verification

Connect a compatible diagnostic scanner (Sumitomo-compatible or multi-brand tool supporting J1939 protocol) to verify the fault code is current, not historical. Clear the code and attempt a cold start to see if it returns. Perform a thorough visual inspection of the glow plug wiring harness, checking for chafing against the engine block, melted insulation, or oil contamination on connectors—common issues in used excavators.

Step 2: Electrical Testing of Glow Plug Circuit

Using a digital multimeter (DMM), disconnect the glow plug control module connector and measure voltage at the power supply terminal with the key in the "ON" position (should read battery voltage, approximately 12-14V). Then check for continuity between the control module output and each individual glow plug terminal. Resistance should typically be 0.5-2.0 ohms per glow plug (consult service manual for exact specifications). High resistance or infinite readings indicate failed glow plugs or open circuits.

Step 3: Test Glow Plug Control Module and Relay

Inspect the glow plug relay for signs of overheating, corrosion, or burnt contacts. With the relay removed, use your multimeter to test relay coil resistance (typically 70-100 ohms) and perform a bench test by applying 12V to activate the relay, verifying proper switching. If the relay functions correctly, the glow plug control module itself may be faulty and require replacement. On used machines, also inspect the ECM connector pins (especially terminals related to glow plug control) for bent pins or "green corrosion" that creates voltage irregularities.

Step 4: Component Replacement and Verification

Replace faulty components starting with the most likely culprits identified during testing. For used excavators with over 3,000 hours, consider replacing all glow plugs simultaneously if one has failed, as others typically fail shortly after. After repairs, clear the fault code, perform multiple cold-start cycles, and monitor with the diagnostic scanner to ensure P0669-3 does not return.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official Sumitomo service manual for your specific serial number and consult a certified heavy equipment technician for complex electrical diagnostics. Improper repairs can cause additional damage or safety hazards.