What is Komatsu PC120-6 Fault Code E317?

Komatsu PC120-6 fault code E317 indicates a malfunction in the pump controller's output signal circuit for the engine speed sensor (Ne sensor), specifically related to an abnormal voltage condition detected by the pump control ECM.

This code targets the communication between the engine control system and the hydraulic pump controller, which relies on accurate engine RPM data to regulate pump displacement and hydraulic output pressure. On the PC120-6 platform, the Ne sensor feeds real-time crankshaft rotational data to both the engine ECM and the pump controller simultaneously.

When this signal is corrupted or lost, the pump controller cannot correctly match hydraulic demand to engine load — a critical function for safe and efficient excavator operation.

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Common Symptoms

When E317 is active on a PC120-6, operators typically report the following:

• Warning lamp illuminates on the monitor panel, often accompanied by the caution buzzer activating at startup or under load
• Hydraulic power reduction or "derating" — the machine feels sluggish and unresponsive during digging or lifting cycles
• Erratic engine RPM behavior, including hunting or surging at idle
• Auto-deceleration failure — the engine does not throttle down correctly during idle periods
• E-mode or L-mode lockout, where the operator cannot switch between working modes via the monitor panel

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Potential Causes

The following are the most frequent technical root causes for E317 on used PC120-6 units:

• Faulty Ne sensor — magnetic pickup sensors degrade over time, particularly in machines with high hours exposed to vibration and heat cycling
• Damaged or chafed signal harness — the wiring loom running from the sensor to the pump controller passes near the engine block and is prone to abrasion on older machines
• Corroded or loose connector pins — moisture ingress at the sensor connector (typically near the flywheel housing) causes intermittent signal dropout
• Pump controller (ECM) internal fault — less common, but controller failures do occur on high-hour PC120-6 machines, especially if the machine has had flood exposure
• Incorrect sensor air gap — if the Ne sensor has been previously replaced without proper calibration, the signal amplitude may fall below the controller's threshold

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How to Troubleshoot and Fix Code E317

Step 1 — Connector and Harness Inspection Begin with a thorough visual inspection of the Ne sensor harness. On used excavators, prioritize checking for wire chafing against the engine block, cracked insulation near clamp points, and corrosion inside the sensor connector. Clean all pins with electrical contact cleaner and apply dielectric grease before reassembly.

Step 2 — Sensor Resistance and Air Gap Check Using a digital multimeter, measure the Ne sensor coil resistance across the sensor terminals. The standard specification for PC120-6 is typically 860–1,060 Ω at ambient temperature — consult your Komatsu shop manual for the precise value. Also verify the physical air gap between the sensor tip and the flywheel gear ring; the gap should be within 0.5–1.5 mm. An incorrect gap produces a weak voltage signal that triggers E317.

Step 3 — Signal Voltage Verification Connect the multimeter in AC millivolt mode and crank the engine. At cranking speed, the Ne sensor should produce a measurable AC output signal. A weak or absent signal with correct resistance confirms a failed sensor. A correct signal with the fault still active points toward a harness open circuit between the sensor and the pump controller connector.

Step 4 — Diagnostic Software Confirmation Use Komatsu KOMTRAX Plus or PC Excavator Troubleshooting (SPAR) software to monitor live Ne sensor data and cross-reference pump controller input values. This confirms whether the fault is sensor-side or controller-side before ordering components.

Step 5 — Component Replacement Replace only the confirmed failed component. If the harness is damaged, repair with appropriately rated shielded cable to maintain signal integrity. After any repair, clear the fault code and perform a full operational test cycle.

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Disclaimer: The diagnostic procedures outlined above are intended as a technical reference for qualified heavy equipment mechanics and experienced operators. Always consult the official Komatsu PC120-6 Shop Manual and adhere to your regional safety regulations before performing electrical or mechanical repairs. If fault code E317 persists after initial diagnostics, consult an authorized Komatsu dealer or certified diesel equipment technician.