Komatsu PC138US-2 Fault Code E101: Technical Guide

What is Komatsu PC138US-2 Fault Code E101?

Fault Code E101 on the Komatsu PC138US-2 indicates a malfunction in the hydraulic oil temperature sensor circuit. This code triggers when the Engine Control Module (ECM) detects abnormal voltage readings from the hydraulic oil temperature sensor, typically outside the manufacturer's specified range of 0.5-4.5 volts.

The hydraulic oil temperature sensor is critical for the PC138US-2's performance monitoring system. It provides real-time data to the ECM, which regulates engine speed, hydraulic pump output, and activates protection modes when oil temperatures exceed safe operating limits (typically above 105°C/221°F). This sensor failure can prevent proper thermal protection, potentially leading to hydraulic system damage or reduced efficiency in older machines where oil cooling capacity may already be compromised.

Common Symptoms

When Code E101 is active on your PC138US-2, operators typically experience:

• Warning light illumination on the instrument panel, often accompanied by an audible alarm
• Reduced hydraulic response or sluggish boom/arm movements as the ECM enters derate mode
• Inaccurate temperature gauge readings showing either maximum, minimum, or erratic fluctuations
• Engine auto-shutdown in extreme cases when the ECM cannot verify safe operating temperatures
• Intermittent code triggering during cold starts or specific operating conditions

Potential Causes

The most common technical causes for Code E101 in used PC138US-2 excavators include:

• Faulty hydraulic oil temperature sensor due to internal thermistor failure (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor harness connection point near the hydraulic tank
• Damaged wiring harness from abrasion against the swing bearing assembly or undercarriage frame
• Poor ground connection at the sensor mounting location due to rust or thread contamination
• ECM internal fault (rare, but possible in high-hour machines with moisture exposure)
• Contaminated hydraulic oil causing sensor coating and false readings

How to Troubleshoot and Fix Code E101

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank's right side). Inspect the wiring harness for physical damage, particularly where it routes past the swing motor and along the frame rails—common wear points on the PC138US-2. Check the connector for corrosion, bent pins, or oil contamination.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to check sensor resistance. At 20°C (68°F), resistance should read approximately 2.5-3.0 kΩ (consult your service manual for exact specifications). Test the harness voltage with the key on: you should see approximately 5 volts supply from the ECM. Check continuity from the sensor ground to chassis ground (should be <1 ohm).

Step 3: Sensor Replacement and Verification If readings fall outside specifications, replace the hydraulic oil temperature sensor (Komatsu part number 7861-93-3320 or equivalent). For used excavators, apply dielectric grease to connector pins before reassembly to prevent future corrosion. Clear the code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then operate the machine through a complete warm-up cycle to verify the fix.

Critical for Used Machines: Before replacing components, thoroughly clean all connector terminals with electrical contact cleaner and inspect for harness chafing at factory routing points—many E101 codes on older PC138US-2s resolve with connector maintenance alone.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number, and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic equipment.