What is Komatsu PC100-6 Fault Code E108?

Komatsu PC100-6 Fault Code E108 indicates a malfunction in the hydraulic oil temperature sensor circuit. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects abnormal voltage readings from the hydraulic oil temperature sensor, typically outside the range of 0.2-4.8 volts.

The hydraulic oil temperature sensor monitors the operating temperature of the hydraulic system, which is critical for maintaining optimal viscosity and preventing component damage. On the PC100-6, this sensor sends real-time temperature data to the ECM, which adjusts pump output and activates warning systems when temperatures exceed safe operating limits (typically above 95°C/203°F). When this circuit fails, the machine cannot properly regulate hydraulic system performance, potentially leading to catastrophic pump or motor failure.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument panel, even when oil feels cool to touch
• Reduced hydraulic performance including slower cycle times and decreased lifting capacity
• Intermittent loss of auxiliary hydraulic functions during operation
• ECM defaulting to fail-safe mode, limiting engine RPM to approximately 1,500 to protect the system
• Erratic temperature gauge readings that fluctuate dramatically or remain at minimum/maximum

Potential Causes

The most common technical causes for E108 on used PC100-6 excavators include:

• Sensor connector corrosion at the hydraulic tank mounting point, where moisture and debris accumulate over years of operation
• Failed hydraulic oil temperature sensor due to internal thermistor degradation (common after 5,000+ operating hours)
• Damaged wiring harness between the sensor and ECM, particularly where the harness routes near the swing bearing—a known rub point on this model
• Poor ground connection at the ECM grounding point near the battery box
• ECM internal fault in the sensor input circuit (rare, but possible on machines with 10+ years of service)
• Aftermarket sensor installation with incorrect resistance specifications (should be approximately 2.5kΩ at 20°C)

How to Troubleshoot and Fix Code E108

Step 1: Visual Inspection Inspect the sensor connector located on the hydraulic tank's right side. Clean any corrosion using electrical contact cleaner and check for bent pins. On used excavators, this connector often fills with hydraulic mist and dirt, causing intermittent failures.

Step 2: Sensor Resistance Check Disconnect the sensor and measure resistance with a digital multimeter. At ambient temperature (20°C/68°F), resistance should read 2.3-2.7kΩ. If outside this range, replace the sensor (Komatsu part# 7861-93-3320).

Step 3: Wiring Harness Continuity Test Check continuity from the sensor connector to ECM pin C-24. Inspect the harness where it passes through the upper structure rotation point—a common wear location. Look for abraded insulation or broken strands.

Step 4: Voltage Supply Verification With ignition ON, verify 5-volt reference supply at the sensor connector (signal wire). If no voltage present, trace back to the ECM for potential internal failure.

Step 5: Ground Circuit Check Measure resistance between sensor ground wire and chassis ground—should be less than 1Ω. Poor grounds are extremely common on used machines with corroded battery terminals.

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Disclaimer: This guide provides general troubleshooting information. Complex electrical diagnostics should be performed by qualified technicians with proper Komatsu diagnostic equipment. Always consult the official service manual for your specific serial number range.