Kato APC150 Fault Code E79: Complete Diagnostic and Repair Guide

What is Kato APC150 Fault Code E79?

Fault Code E79 on the Kato APC150 excavator indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal temperature reading exceeding safe operating limits. This code is triggered when the Electronic Control Unit (ECU) detects either a sensor voltage outside the expected range (typically 0.5-4.5V) or an actual hydraulic oil temperature above critical thresholds (usually 90-95°C).

This fault is particularly critical for the APC150 because excessive hydraulic temperatures can cause rapid degradation of seals, decreased hydraulic efficiency, and potential component failure. The hydraulic system temperature sensor provides essential data for the ECU to regulate pump output and protect the system from thermal damage.

Common Symptoms

• Warning light illumination on the instrument panel, often accompanied by an audible alarm
• Reduced hydraulic power or sluggish operation as the ECU enters derate mode to protect components
• Erratic temperature gauge readings or gauge pegged at maximum/minimum positions
• Intermittent code activation that clears and returns, especially when operating in hot conditions
• Complete loss of hydraulic function in severe cases where the ECU initiates shutdown protocol

Potential Causes

The E79 code typically stems from issues common in used excavators:

• Hydraulic oil temperature sensor failure due to age-related degradation or thermal cycling stress
• Damaged wiring harness at known rub points near the hydraulic tank mounting bracket or along the main boom
• Corroded connector pins at the sensor plug, especially on machines operated in coastal or high-humidity environments
• Actual hydraulic system overheating caused by clogged oil coolers, low oil levels, or failing cooling fans
• ECU calibration drift or internal ECU fault (less common but possible in high-hour machines)
• Poor electrical grounding at the sensor mounting point due to rust or loose fasteners

How to Troubleshoot and Fix Code E79

Step 1: Visual Inspection Begin with a thorough inspection of the hydraulic oil temperature sensor located on the hydraulic tank (typically mounted on the return filter housing). Check the wiring harness for abrasion, cuts, or heat damage along its entire length, paying special attention to areas where the harness contacts the frame.

Step 2: Electrical Testing Using a digital multimeter (DVOM), disconnect the sensor connector and measure resistance across the sensor terminals. At 20°C ambient temperature, resistance should typically read 2,000-3,000 ohms (consult service manual for exact specifications). Check continuity in the wiring from sensor to ECU connector pins. Measure voltage supply from the ECU—you should see approximately 5V reference voltage.

Step 3: Physical Sensor and System Checks For used excavators, verify actual hydraulic oil temperature using an infrared thermometer at the tank surface. Clean all connector terminals with electrical contact cleaner and apply dielectric grease. Check hydraulic oil level and condition—contaminated or low oil causes genuine overheating. Inspect the hydraulic oil cooler for debris blockage.

Step 4: Component Replacement If testing confirms sensor failure, replace with OEM or quality aftermarket temperature sensor, ensuring proper torque specifications (typically 15-20 N⋅m). On high-hour machines, consider replacing the connector pigtail simultaneously to prevent future corrosion issues.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Kato service manual for your specific serial number range. For complex electrical diagnostics or critical repairs, consult a certified heavy equipment technician with Kato-specific diagnostic software.