What is Komatsu PC200LC-7 Fault Code E318?

Komatsu PC200LC-7 fault code E318 indicates a malfunction in the Hydraulic Oil Temperature Sensor Circuit, specifically detecting an abnormal voltage signal or open/short circuit condition in the sensor wiring harness. This code is triggered when the Electronic Control Module (ECM) receives voltage readings outside the expected range (typically 0.5-4.5V) from the hydraulic oil temperature sensor located in the main hydraulic tank.

This fault is critical for the PC200LC-7 because the ECM relies on accurate hydraulic oil temperature data to regulate engine speed, prevent thermal damage to hydraulic components, and optimize fuel efficiency. When this sensor circuit fails, the machine may enter protective derate mode or disable certain high-demand hydraulic functions, significantly reducing productivity on the job site.

Common Symptoms

• Amber warning light illuminated on the instrument cluster with E318 displayed on the monitor panel
• Reduced hydraulic response or slower cycle times, particularly during cold starts or after extended operation
• Engine may automatically reduce RPM to low idle mode when hydraulic oil reaches certain thresholds
• Intermittent loss of auxiliary hydraulic functions (breaker, thumb, or multi-processor attachments)
• Audible warning alarm that activates during high-temperature conditions, even when oil temperature appears normal

Potential Causes

The most common technical failures causing E318 on used PC200LC-7 excavators include:

• Damaged or corroded wiring harness at the sensor connector, especially where the harness passes near the swing motor or along the undercarriage (known rub point on this model)
• Failed hydraulic oil temperature sensor due to internal thermistor deterioration or moisture intrusion
• Corroded connector pins at the 3-pin Deutsch connector between the sensor and main harness (common on machines operating in wet/corrosive environments)
• ECM internal fault in the analog-to-digital converter circuitry (rare, but documented on high-hour units)
• Broken or frayed wiring inside the engine compartment near exhaust components due to heat stress
• Previous repair attempts using non-OEM sensors with incorrect resistance curves

How to Troubleshoot and Fix Code E318

Step 1: Visual Inspection and Connector Check Begin by locating the hydraulic oil temperature sensor on the left side of the main hydraulic tank. Disconnect the 3-pin connector and inspect for green corrosion, bent pins, or oil contamination. On used excavators, this connector frequently shows corrosion damage. Clean with electrical contact cleaner and apply dielectric grease before reconnecting.

Step 2: Sensor Resistance Testing Using a digital multimeter (DMM), measure resistance across the sensor terminals with the sensor removed from the tank. At 68°F (20°C), resistance should read approximately 2,200-2,800 ohms. Compare readings against Komatsu's temperature-resistance chart. Replace the sensor if readings deviate by more than 10% or show infinite resistance (open circuit).

Step 3: Harness Continuity and Voltage Check With the sensor disconnected, check for 5-volt reference voltage at the harness connector (key on, engine off). Verify continuity between the sensor ground pin and chassis ground (should read less than 1 ohm). Inspect the harness routing from the tank to the ECM near the operator's cab, paying special attention to areas where the harness crosses metal edges or moving components—these are common failure points on machines with 5,000+ hours.

Step 4: Clear Code and Monitor After repairs, use Komatsu diagnostic software (KOMTRAX Plus) or a compatible scan tool to clear the fault code. Operate the machine through a complete warm-up cycle while monitoring live sensor data. The temperature reading should climb gradually from ambient to 140-180°F during normal operation.

For used excavators specifically, always inspect the wire harness routing for signs of previous modifications or repairs, as aftermarket harness repairs often use inferior wire gauge or inadequate heat protection.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu service manual for your specific serial number and consult qualified Komatsu-certified technicians for complex electrical diagnostics or ECM replacement procedures.