Komatsu PC800-7 Fault Code E315: Complete Diagnostic Guide

What is Komatsu PC800-7 Fault Code E315?

Fault Code E315 on the Komatsu PC800-7 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open/short circuit condition in the sensor wiring harness. This code is generated when the Engine Control Module (ECM) receives voltage readings outside the predetermined range (typically below 0.2V or above 4.8V) from the coolant temperature sensor.

The coolant temperature sensor is critical for the PC800-7's performance because it directly influences fuel injection timing, engine protection protocols, and hydraulic oil temperature management. When this sensor fails, the ECM defaults to a predetermined temperature value, potentially causing inefficient combustion, increased emissions, and inadequate engine protection during cold starts or overheating conditions.

Common Symptoms

• Warning lamp illuminated on the instrument cluster with reduced engine power output
• Engine running in derate mode (limited to approximately 70-80% power)
• Difficulty starting in cold weather conditions due to improper fuel enrichment
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Erratic temperature gauge readings or gauge stuck at minimum/maximum position

Potential Causes

The most common causes of E315 on used PC800-7 excavators include:

• Coolant temperature sensor internal failure due to age and thermal cycling (typical lifespan: 5,000-8,000 operating hours)
• Corroded or damaged connector pins at the sensor or ECM connection points
• Wiring harness chafing near the engine block mounting points or along the frame rail where vibration causes insulation wear
• Moisture intrusion in the sensor connector causing intermittent short circuits
• Failed ECM internal circuitry (rare, but documented in high-hour machines)
• Improper coolant mixture causing sensor element degradation

How to Troubleshoot and Fix Code E315

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor (located on the engine block near the thermostat housing) and its connector for obvious damage, corrosion, or coolant leaks. On used excavators, check for harness wear at known rub points along the engine valley and frame crossmembers.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms. Check wiring harness continuity from sensor to ECM and verify no shorts to ground (should read infinite resistance).

Step 3: Signal Voltage Verification With the sensor connected and ignition on (engine off), backprobe the sensor connector and measure voltage. You should see approximately 5V reference voltage from the ECM. If voltage is absent, trace the harness for breaks or check ECM power supply circuits.

Step 4: Component Replacement Replace the sensor if resistance values are incorrect. For used machines, always apply dielectric grease to connector pins and secure harnesses away from heat sources and moving components to prevent recurrence.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual and consider professional diagnostic assistance for complex electrical issues or ECM-related problems.