What is Komatsu PC120-6 Fault Code H-32?

Komatsu PC120-6 fault code H-32 indicates an abnormality in the pump controller's communication system — specifically, a failure in the data link between the pump controller (PC) and the engine controller (EC), resulting in a loss of coordinated control signal transmission.

On the PC120-6, the pump and engine controllers must continuously exchange operational data to optimize hydraulic output and engine load matching. When this CAN communication link is interrupted or degraded, the machine cannot regulate pump displacement relative to engine speed — a critical function for both efficiency and component protection.

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Common Symptoms

Operators and technicians typically report the following when H-32 is active:

• Warning lamp illumination on the monitor panel, often accompanied by an audible alarm
• Reduced hydraulic response — attachments and swing feel sluggish or unresponsive
• Engine and pump desynchronization, causing noticeable hunting or irregular RPM behavior under load
• Possible power derate mode activation, limiting machine output to prevent damage
• Error code displayed on the Komatsu monitor unit alongside potential concurrent controller fault codes

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Potential Causes

The following are the most frequently identified root causes of H-32 on the PC120-6:

• Damaged or corroded CAN bus wiring harness between the pump controller and engine controller — a common issue on used machines with high operating hours
• Loose or oxidized connector pins at the pump controller (PC) or engine controller (EC) junction points, particularly in high-vibration mounting areas
• Harness chafing along the firewall or frame routing points, a known wear location on this model
• Failed pump controller (PC unit) — internal communication chip failure after prolonged heat and vibration exposure
• ECU power supply irregularities — low or unstable voltage to either controller disrupting data link initialization

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How to Troubleshoot and Fix Code H-32

Step 1 — Retrieve and Document All Active Codes Connect Komatsu KOMTRAX or a compatible diagnostic interface (such as Komatsu PC Excavator Diagnostics software) to the machine's diagnostic port. Record all active and stored fault codes. Multiple concurrent codes often point to a wiring or power supply issue rather than a failed controller.

Step 2 — Inspect the Wiring Harness and Connectors Physically trace the CAN bus harness routing between the pump controller and engine controller. On used PC120-6 units, pay close attention to harness segments near the hydraulic pump housing, engine firewall grommets, and any cable ties that may have worn through the insulation. Look for corrosion, green oxidation, or pin-back in the multi-pin connectors.

Step 3 — Perform Voltage and Resistance Checks Using a digital multimeter, verify:

• Battery voltage at both controllers: should read 24V DC (±1V) with the key on
• CAN High/CAN Low line resistance: measure between CAN-H and CAN-L terminals — nominal resistance should be approximately 60 ohms across the terminated network

Step 4 — Clean, Repair, or Replace Apply electrical contact cleaner and dielectric grease to all inspected connectors. Repair or replace any chafed harness sections using appropriately rated shielded cable. If wiring integrity is confirmed but the fault persists, the pump controller unit should be tested on a known-good machine before replacement.

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Disclaimer: This guide is intended for qualified heavy equipment technicians and experienced operators. Fault diagnosis on electronic control systems involves working with sensitive components. Always consult the official Komatsu PC120-6 Shop Manual and seek assistance from a certified Komatsu dealer or licensed diesel mechanic before replacing major components.