What is Komatsu PC120LC-6 Fault Code E233?

Fault Code E233 indicates a malfunction in the hydraulic pilot pressure sensor circuit. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the pilot pressure sensor, which monitors the hydraulic pressure used to control the machine's working equipment and travel functions.

The pilot pressure sensor is critical for the PC120LC-6's performance because it provides real-time feedback to the ECM about hydraulic system demand. When this sensor fails or sends incorrect signals, the ECM cannot properly regulate engine output to match hydraulic loads, potentially causing inefficient operation, reduced productivity, and component stress. This code is particularly important in used machines where sensor degradation and wiring deterioration are common.

Common Symptoms

• Reduced engine power or inability to reach maximum RPM under load
• Erratic operation of joystick controls, including sluggish or inconsistent response
• Warning lamp illumination on the instrument cluster (often the amber caution indicator)
• Intermittent loss of hydraulic functions, especially during cold starts or high-demand operations
• Abnormal engine derating where the machine limits power output automatically

Potential Causes

The most common technical causes for Code E233 on used PC120LC-6 excavators include:

• Pilot pressure sensor failure due to internal wear, contamination, or diaphragm rupture
• Damaged wiring harness between the sensor and ECM, particularly at flex points near the operator's cab or around the hydraulic pump area where harness rubbing is common
• Corroded or loose connector pins at the sensor plug or ECM connections, typical in machines operating in wet or corrosive environments
• Short circuit to ground or power in the sensor signal wire, often caused by wire insulation degradation
• ECM voltage supply issues providing incorrect reference voltage to the sensor (typically should be 5V)

How to Troubleshoot and Fix Code E233

Step 1: Visual Inspection Begin by inspecting the pilot pressure sensor (located on the hydraulic pilot valve block) and its wiring harness. Check for obvious physical damage, oil contamination, corrosion on connector terminals, or abraded wires. On used excavators, pay special attention to harness routing near moving components where friction wear commonly occurs.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's output voltage with the ignition on. The pilot pressure sensor should output approximately 0.5-4.5 volts depending on pressure. Also verify the ECM reference voltage at the sensor connector (should be 5V ±0.25V). Check resistance in the signal wire from sensor to ECM—it should be less than 5 ohms.

Step 3: Sensor Replacement or Repair If voltage readings are out of specification or erratic, replace the pilot pressure sensor with a genuine Komatsu part (Part #: 7861-93-1650). Before replacement, clean all connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. If wiring damage is found, repair using OEM-spec wiring and proper heat-shrink connectors—avoid simple tape repairs on used machines.

Step 4: Clear Code and Verify After repairs, clear the fault code using Komatsu KOMTRAX diagnostic software or a compatible scan tool. Operate the machine through full working cycles and monitor for code reoccurrence.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.