Komatsu PC120LC-6 Fault Code E317: Complete Diagnostic Guide

What is Komatsu PC120LC-6 Fault Code E317?

Fault Code E317 indicates a malfunction in the engine coolant temperature sensor circuit, specifically an abnormal voltage signal detected by the Engine Control Module (ECM). This code triggers when the ECM receives either an excessively high or low voltage reading from the coolant temperature sensor, preventing accurate monitoring of engine operating temperatures.

For the PC120LC-6's SAA4D102E-2 engine, this sensor plays a critical role in fuel injection timing, engine protection systems, and idle speed control. When E317 activates, the ECM typically defaults to a predetermined temperature value, which can compromise engine efficiency and potentially lead to overheating or excessive fuel consumption.

Common Symptoms

• Yellow warning light illuminated on the instrument panel with reduced engine power output
• Rough idling or hunting at low RPM, especially during cold starts
• Black smoke from the exhaust due to incorrect fuel mapping
• Engine running cooler or hotter than normal operating temperature (80-95°C)
• Delayed warm-up periods with the engine remaining in high-idle mode longer than usual

Potential Causes

The most frequent causes of E317 on used PC120LC-6 excavators include:

• Corroded or loose connector pins at the coolant temperature sensor (common failure point after 5,000+ operating hours)
• Failed coolant temperature sensor due to thermal cycling and coolant contamination
• Damaged wiring harness near the thermostat housing where vibration causes wire chafing against metal brackets
• Poor ground connections at the ECM or sensor ground circuit
• Coolant contamination on sensor tip causing erratic resistance readings
• ECM internal fault (rare, but seen in machines with water ingress history)

How to Troubleshoot and Fix Code E317

Step 1: Visual Inspection Locate the coolant temperature sensor on the thermostat housing (driver's side of engine block). Inspect the two-wire connector for corrosion, bent pins, or moisture. Check the wiring harness from sensor to ECM for abrasion points, particularly where it passes near the fuel filter bracket.

Step 2: Sensor Resistance Testing Disconnect the sensor and measure resistance using a digital multimeter. At 20°C (68°F), resistance should read approximately 2.3-2.7 kΩ; at 80°C (176°F), approximately 0.3-0.4 kΩ. Values outside this range indicate sensor failure.

Step 3: Circuit Voltage Check With ignition on and sensor disconnected, measure voltage at the ECM-side connector. You should see approximately 5V reference voltage on the signal wire. No voltage indicates wiring issues or ECM problems.

Step 4: Harness Continuity Test Test continuity between sensor connector and ECM pins (refer to service manual for specific pin locations). On used excavators, pay special attention to connector seals and check for green corrosion inside terminals—a common issue in machines operating in high-humidity environments.

Step 5: Replacement and Verification If sensor tests faulty, replace with genuine Komatsu part 6732-81-3140. Apply dielectric grease to connector before reinstallation. Clear codes using Komatsu diagnostic software (KOMTRAX) or compatible scan tool, then run engine through full temperature cycle to verify repair.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional assistance for complex electrical diagnostics.