What is Komatsu PC220-7 Fault Code E308?

Komatsu PC220-7 fault code E308 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. This diagnostic trouble code (DTC) is logged by the machine's Engine Control Module (ECM) when it receives voltage readings outside the normal operating range (typically 0.5-4.5V) from the hydraulic oil temperature sensor.

The hydraulic oil temperature sensor plays a critical role in the PC220-7's performance management system. It monitors the operating temperature of hydraulic fluid to prevent overheating, optimize hydraulic pump efficiency, and protect sensitive components. When this sensor fails or sends inaccurate data, the ECM may limit machine functions or trigger warning systems to prevent catastrophic hydraulic system damage.

Common Symptoms

When code E308 is active on your Komatsu PC220-7, operators typically experience:

• Illuminated warning lamp on the instrument panel (often amber/yellow hydraulic system indicator)
• Inaccurate hydraulic oil temperature readings displayed on the monitor or stuck at minimum/maximum values
• Reduced hydraulic performance as the ECM may enter a protective derate mode
• Intermittent activation of cooling fans regardless of actual operating temperature
• Machine may enter limp mode in severe cases, limiting swing speed and travel functions

Potential Causes

The most common technical causes for E308 on used PC220-7 excavators include:

• Worn or corroded sensor connector pins (extremely common in machines with 5,000+ hours due to exposure to moisture and vibration)
• Damaged wiring harness from rubbing against the hydraulic tank mounting brackets or pump assembly
• Failed hydraulic oil temperature sensor due to internal element degradation or thermal cycling fatigue
• Poor ground connection at the sensor mounting point caused by rust or paint buildup
• ECM internal fault (rare, but possible in high-hour machines with electrical system history)

How to Troubleshoot and Fix Code E308

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor mounted on the hydraulic tank (typically on the left side near the return filter). Inspect the sensor connector for corrosion, bent pins, or oil contamination. Check the wiring harness along its entire route for chafing, particularly where it passes near metal edges or moving components. On used excavators, this is the most common failure point.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should read approximately 2,000-3,000 ohms (refer to Komatsu service manual for exact specifications). Test the harness continuity from the ECM connector to the sensor plug—readings should show less than 5 ohms resistance and infinite resistance to ground.

Step 3: Voltage Signal Check With the ignition on and sensor connected, backprobe the signal wire at the sensor connector. You should see approximately 5V reference voltage from the ECM. If voltage is absent, trace the reference voltage circuit back to the ECM for breaks or shorts.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu part (P/N 7861-93-3320 or equivalent). Clean all connector pins with electrical contact cleaner and apply dielectric grease before reconnection. Clear codes using Komatsu diagnostic software (KDPF) and verify repair with a test cycle.

For used excavators with persistent issues after sensor replacement, inspect the ECM connector terminals and consider updating ECM software, as older firmware versions may have known sensor sensitivity issues.

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Disclaimer: This guide provides general troubleshooting information for trained technicians. Always consult the official Komatsu PC220-7 service manual and follow proper safety procedures. If you lack the necessary diagnostic tools or experience, contact a certified Komatsu dealer or qualified heavy equipment technician.