What is Komatsu PC120LC-6 Fault Code E315?

Fault Code E315 on the Komatsu PC120LC-6 indicates a Swing Motor Overheat condition detected by the excavator's monitoring system. This code triggers when the temperature sensor integrated into the swing motor assembly detects temperatures exceeding the manufacturer's safe operating threshold, typically above 100-110°C (212-230°F).

The swing motor on the PC120LC-6 is a critical hydraulic component responsible for rotating the upper structure. When overheating occurs, the Electronic Control Module (ECM) logs the fault to prevent catastrophic damage to internal seals, bearings, and hydraulic oil integrity. This protection mechanism is vital because swing motor replacement on used excavators can cost $3,000-$8,000 in parts alone, making early detection crucial for equipment longevity.

Common Symptoms

When Code E315 is active, operators typically experience:

• Audible warning alarm accompanied by a red warning light on the instrument cluster
• Reduced swing speed or swing function temporarily disabled as the system enters protective derate mode
• Abnormal heat radiating from the swing motor housing, detectable during physical inspection
• Jerky or inconsistent rotation of the upper structure during operation
• Hydraulic oil discoloration or burning smell near the swing motor area in severe cases

Potential Causes

The most common technical causes for E315 on used PC120LC-6 excavators include:

• Restricted swing motor cooling circuit due to clogged or damaged heat exchanger fins
• Degraded swing bearing grease causing increased friction and heat generation (common after 6,000+ operating hours)
• Faulty temperature sensor or corroded wiring harness connections near the swing motor
• Excessive hydraulic pressure to the swing circuit from contaminated or worn relief valves
• Low hydraulic oil level or use of incorrect viscosity oil reducing heat dissipation efficiency
• Damaged wiring harness from rubbing against the swing bearing race during rotation (a known wear point on this model)

How to Troubleshoot and Fix Code E315

Step 1: Initial Inspection Allow the machine to cool completely. Physically inspect the swing motor housing for excessive dirt buildup blocking cooling fins. Check hydraulic oil level and condition—milky or burnt oil indicates contamination. On used excavators, examine the wiring harness routing around the swing bearing for abrasion or exposed wires.

Step 2: Temperature Sensor Testing Using a digital multimeter, disconnect the temperature sensor connector (located on the swing motor housing). Measure resistance across sensor terminals—specifications typically range 200-500 ohms at 20°C ambient temperature. Compare readings against Komatsu service manual specifications. Inspect connector pins for corrosion or moisture intrusion, common in machines operating in wet conditions.

Step 3: Hydraulic System Diagnostics Connect Komatsu diagnostic software (KOMTRAX or equivalent) to read real-time swing motor temperature and pressure data. Monitor swing circuit pressure during operation—normal values should be 280-320 bar. Excessive pressure indicates potential relief valve failure. Test swing motor case drain flow; restricted flow suggests internal bearing wear.

Step 4: Mechanical Assessment For used excavators with high hours, check swing bearing grease condition through grease ports. Dark or gritty grease indicates bearing wear generating excessive heat. Rotate the upper structure manually (engine off) feeling for rough spots or binding—indicators of bearing deterioration requiring replacement before motor damage occurs.

Step 5: Corrective Actions Replace the temperature sensor if readings are out of specification ($150-$250 part). Clean or replace the swing motor heat exchanger. Flush and refill with manufacturer-specified hydraulic oil. If bearing wear is confirmed, schedule immediate swing bearing service to prevent E315 recurrence and costly motor replacement.

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Disclaimer: This guide provides general troubleshooting procedures. Always consult the official Komatsu PC120LC-6 service manual and consider professional diagnostic assistance for complex hydraulic or electrical issues, especially on high-hour used equipment.