What is Komatsu PC450-7 Fault Code E-24?

Fault Code E-24 on the Komatsu PC450-7 excavator indicates a malfunction in the Hydraulic Oil Temperature Sensor Circuit, specifically detecting an abnormally high voltage signal or open circuit condition in the sensor wiring.

This diagnostic trouble code is triggered when the machine's Electronic Control Module (ECM) receives a voltage reading outside the specified range (typically above 4.5V) from the hydraulic oil temperature sensor located in the main hydraulic tank. The PC450-7's hydraulic system relies on precise temperature monitoring to protect expensive pumps, motors, and control valves from thermal damage. When this sensor circuit fails, the ECM cannot accurately monitor oil temperatures, potentially leading to component overheating and reduced operational efficiency. For used excavators, this code is particularly important as deteriorated wiring and corroded connectors are common failure points that can cause catastrophic hydraulic system damage if ignored.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument cluster, even when the machine is cold or after minimal operation
• Erratic temperature gauge readings that jump between minimum and maximum values or remain pegged at maximum
• Machine may enter derate mode (reduced engine RPM or hydraulic power) if the ECM defaults to a fail-safe high-temperature assumption
• Intermittent code activation that appears and disappears, especially when the machine vibrates during operation or boom/arm movement
• Abnormal fan operation with cooling fans running continuously at high speed regardless of actual oil temperature

Potential Causes

Broken or frayed sensor wiring is the most common issue in used PC450-7 excavators, particularly where the harness routes near the hydraulic tank mounting brackets or along the swing bearing area where constant machine movement causes wire insulation to wear through.

Corroded or loose electrical connectors at the sensor itself or at the main wiring harness connection points create intermittent high-resistance conditions that the ECM interprets as an open circuit.

Failed hydraulic oil temperature sensor with internal element breakage, though less common than wiring issues in machines with over 5,000 operating hours.

Damaged ECM connector pins (specifically the sensor signal and ground pins) due to moisture intrusion or improper previous repair attempts.

Grounding issues where the sensor ground wire has corroded at its chassis mounting point, creating voltage reference problems.

How to Troubleshoot and Fix Code E-24

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 sensor's 2-pin connector and carefully inspect both the sensor-side and harness-side terminals for corrosion, bent pins, or oil contamination. On used excavators, this connector frequently shows green corrosion due to hydraulic oil mist exposure. Clean connectors with electrical contact cleaner and examine the wiring harness from the sensor back to the bulkhead connector for any visible damage, especially where the harness passes near sharp edges or rotating components.

Step 2: Sensor Resistance Testing

Using a digital multimeter, measure the resistance across the sensor terminals with the sensor disconnected. At approximately 20°C (68°F), the sensor should read between 2,000-3,000 ohms. If you see an open circuit (infinite resistance) or readings significantly outside this range, the sensor has failed and requires replacement (Komatsu part number 7861-93-3320 or equivalent). For used machines, also physically inspect the sensor body for cracks or damage from impacts during tank servicing.

Step 3: Circuit Voltage and Wiring Verification

Reconnect the sensor and perform a backprobe test at the ECM connector (located behind the operator's seat). With ignition on and engine off, measure voltage between the sensor signal wire (typically a white/blue wire at ECM pin C-22) and chassis ground. You should see approximately 5V reference voltage. If voltage is absent or incorrect, trace the wiring for breaks or shorts. Pay special attention to areas where harnesses route through the swing bearing area and near the hydraulic pump mounting - these are notorious rub points on the PC450-7. Use Komatsu KOMTRAX diagnostic software or a compatible CAN diagnostic tool to monitor live sensor data and verify the ECM is receiving proper signals after repairs.

For used excavators specifically: Before replacing any components, thoroughly inspect all harness protection sleeves and wire loom routing. Many E-24 codes are resolved simply by re-routing damaged harnesses away from wear points and properly securing them with new cable ties and protective conduit.

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Disclaimer: This guide provides general troubleshooting information for the Komatsu PC450-7. Always consult the official Komatsu service manual for your specific machine serial number, and consider engaging a certified Komatsu technician for complex electrical diagnostics. Improper repairs may void warranties or create safety hazards.