Komatsu PC200-7 Fault Code E308: Complete Diagnostic Guide

What is Komatsu PC200-7 Fault Code E308?

Fault Code E308 on the Komatsu PC200-7 excavator indicates a Hydraulic Oil Temperature Sensor Circuit malfunction, specifically detecting an abnormal voltage signal from the sensor to the Engine Control Module (ECM). This code typically triggers when the sensor circuit experiences an open circuit, short circuit, or sends voltage readings outside the normal operating range of 0.5-4.5 volts.

The hydraulic oil temperature sensor is critical for the PC200-7's performance because it allows the ECM to monitor and protect the hydraulic system from overheating. When this sensor fails, the machine may enter a protective derate mode or prevent optimal hydraulic performance, which directly impacts productivity and can lead to expensive component damage if ignored.

Common Symptoms

• Warning lamp illumination on the instrument panel with reduced engine power
• Sluggish hydraulic response across all functions (boom, arm, bucket, and swing)
• Erratic temperature gauge readings or gauge stuck at minimum/maximum position
• Engine derate mode activating during normal operating conditions, limiting RPM to approximately 1,500
• Intermittent code appearance, especially when operating in wet conditions or after machine warmup

Potential Causes

The E308 code on used PC200-7 excavators commonly stems from age-related deterioration:

• Corroded or damaged wiring harness near the hydraulic tank area where the sensor mounts (known rub point on this model)
• Failed hydraulic oil temperature sensor due to thermal cycling fatigue over thousands of operating hours
• Moisture intrusion into the sensor connector, causing intermittent short circuits
• Broken or frayed wires at the harness connector behind the operator's cab where the main harness passes through
• ECM internal circuit failure (rare, but possible on high-hour machines)
• Poor ground connection at the sensor mounting point due to rust or hydraulic fluid contamination

How to Troubleshoot and Fix Code E308

Step 1: Visual Inspection Locate the hydraulic oil temperature sensor on the left side of the hydraulic oil tank. Inspect the sensor connector for corrosion, bent pins, or oil contamination. Check the wiring harness for visible damage, especially where it routes along the tank and through cab bulkheads—common wear points on used PC200-7 models.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure resistance. At 77°F (25°C), the sensor should read approximately 2.2-2.8 kΩ. Next, check circuit continuity from the ECM connector (Pin 37) to the sensor connector. Resistance should be less than 1 ohm. Measure voltage supply at the sensor connector with ignition on—you should see approximately 5 volts.

Step 3: Component Replacement If testing confirms sensor failure, replace with Komatsu OEM part number 7861-93-1650 or verified equivalent. For used excavators, always apply dielectric grease to connector pins during reassembly to prevent future moisture issues. If wiring shows damage, repair or replace the affected harness section rather than relying on temporary splices.

Step 4: Clear Code and Verify Use Komatsu diagnostic software (KOMTRAX) or a compatible scanner to clear the fault code. Operate the machine through a complete warm-up cycle and monitor for code recurrence.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC200-7 service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-voltage systems.