Komatsu PC35MR-2 Fault Code H-20: Complete Diagnostic Guide

What is Komatsu PC35MR-2 Fault Code H-20?

Fault Code H-20 on the Komatsu PC35MR-2 indicates a malfunction in the travel motor sensor circuit, specifically detecting an abnormal signal from the left or right travel motor speed sensor system. This code triggers when the machine's ECM (Engine Control Module) receives voltage readings outside the expected parameters from the travel motor's magnetic pickup sensor.

This diagnostic trouble code is critical for the PC35MR-2's performance because the travel motor sensors provide essential feedback to the hydraulic control system. When the ECM cannot accurately monitor travel motor speed, it may limit machine functions to prevent damage to the hydrostatic transmission system. On used excavators, this fault often results from sensor degradation or wiring harness issues rather than catastrophic component failure.

Common Symptoms

When fault code H-20 is active, operators typically experience:

• Warning light illumination on the instrument panel with possible audible alarm
• Reduced travel speed or jerky movement in one or both tracks
• Intermittent loss of straight tracking, causing the machine to pull to one side
• Hydraulic system responsiveness issues during simultaneous travel and work operations
• Error code display on the monitor screen (model-specific digital displays)

Potential Causes

The most common technical reasons for H-20 appearing on used PC35MR-2 excavators include:

• Travel motor speed sensor failure due to internal component degradation or contamination from metal debris in hydraulic fluid
• Damaged or corroded wiring harness at connector points near the travel motors (high-vibration area)
• Broken sensor mounting hardware causing air gap issues between the sensor and tone wheel
• Connector pin corrosion from water intrusion in the undercarriage environment
• ECM internal fault (rare, but possible in high-hour machines with 8,000+ operating hours)
• Intermittent short circuits caused by harness rubbing against the travel motor housing

How to Troubleshoot and Fix Code H-20

Step 1: Visual Inspection Begin by inspecting both travel motor sensor connectors for obvious damage. Look for corroded pins, pushed-back terminals, or moisture inside connector housings. On used excavators, check for harness wear where cables route along the undercarriage frame—this is a known rub point on the PC35MR-2.

Step 2: Electrical Testing Using a digital multimeter, measure resistance across the sensor terminals with the connector disconnected. The travel motor speed sensor should read approximately 800-1200 ohms at room temperature (consult your service manual for exact specifications). Check for continuity between sensor ground and chassis ground. Measure supply voltage at the ECM connector (typically 5-8V reference voltage).

Step 3: Signal Testing Reconnect the sensor and use Komatsu KOMTRAX diagnostic software or a compatible scan tool to monitor live sensor data. Manually rotate the travel motor and observe frequency changes. An erratic signal or no signal indicates sensor failure.

Step 4: Physical Sensor Inspection Remove the sensor from the travel motor housing. Inspect the tone wheel (pickup target) for damage or excessive buildup of metallic debris. Verify the air gap between sensor tip and tone wheel is within specification (typically 0.5-1.5mm). Clean all metal shavings from the magnetic sensor tip.

Step 5: Replacement Protocol If testing confirms sensor failure, replace with a genuine Komatsu sensor or OEM-equivalent part. For used excavators, always replace both the sensor and connector pigtail together to prevent future corrosion issues. Apply dielectric grease to all connector pins before reassembly.

---

Disclaimer: This guide provides general diagnostic procedures for educational purposes. Always consult the official Komatsu PC35MR-2 service manual for model-specific specifications. Complex electrical issues or hydraulic system repairs should be performed by certified Komatsu technicians with proper diagnostic equipment.