What is Komatsu PC120-6 Fault Code H-15?

Komatsu PC120-6 fault code H-15 indicates an abnormality in the pump control solenoid valve circuit — specifically, an open or short circuit detected in the main hydraulic pump's PC (pressure compensation) solenoid valve.

This code is generated when the ECM (Engine Control Module) detects that the signal sent to the PC solenoid valve falls outside the expected current range. On the PC120-6, this solenoid directly governs hydraulic pump displacement, regulating flow output in response to load demands. A fault here compromises the machine's ability to match pump output to working conditions, which directly impacts both fuel efficiency and hydraulic performance.

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Common Symptoms

When fault code H-15 is active on a Komatsu PC120-6, operators typically report the following:

• Warning lamp illumination on the monitor panel, often accompanied by an audible alarm
• Reduced hydraulic power or sluggish boom, arm, and bucket response during normal digging cycles
• Engine lugging or hunting under load due to uncontrolled pump displacement
• Abnormal heat buildup in the hydraulic system caused by inefficient flow regulation
• Machine entering a limp or derate mode, limiting maximum engine RPM and hydraulic output to protect components

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Potential Causes

The following are the most likely technical causes of the H-15 code on this model:

• Open circuit in the PC solenoid valve wiring harness — a common failure point where the harness routes beneath the cab or along the boom foot on used machines
• Internal short circuit within the PC solenoid coil itself, caused by coil insulation breakdown from heat exposure or age
• Corroded or damaged connector pins at the solenoid plug or ECM connector, particularly on machines operating in wet or muddy environments
• Faulty ECM output driver — less common but possible on high-hour units with prior electrical damage
• Hydraulic contamination causing solenoid spool seizure, forcing abnormal current draw detectable by the ECM

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How to Troubleshoot and Fix Code H-15

Step 1 — Inspect the Harness and Connectors First On a used excavator, always begin with a thorough visual inspection. Trace the wiring harness from the ECM to the PC solenoid, checking for chafing, pinch points, or corrosion. Pay close attention to harness routing near the swing frame and undercarriage covers — common friction points on the PC120-6. Clean corroded pins with electrical contact cleaner before proceeding.

Step 2 — Measure Solenoid Coil Resistance Disconnect the solenoid connector and use a digital multimeter set to the Ohms (Ω) function. Measure resistance across the solenoid terminals. The PC120-6 PC solenoid typically reads approximately 18–22 Ω at ambient temperature. A reading of 0 Ω (short) or OL/infinite (open) confirms solenoid coil failure — replace the solenoid valve assembly.

Step 3 — Check Circuit Voltage at the ECM Using Komatsu's KOMTRAX Plus or a compatible diagnostic interface (such as Komatsu PC Excavator Monitoring System software), monitor live solenoid output current. Verify that the ECM is commanding correct current output. Check supply voltage at the harness connector with the key-on; you should see battery voltage (approximately 24V DC) present before the ECM grounds the circuit.

Step 4 — Verify and Clear After completing repairs, clear the fault code using the diagnostic tool and cycle the machine through a full operating sequence. Confirm the code does not return and that hydraulic response has normalized.

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Disclaimer: The diagnostic information provided here is intended as a general technical reference for qualified mechanics and experienced equipment owners. Fault diagnosis on hydraulic and electronic systems can involve high-pressure fluids and live electrical circuits. Always consult the official Komatsu PC120-6 Shop Manual and, when in doubt, engage a certified Komatsu dealer or qualified heavy equipment technician before performing repairs.