Komatsu PC850-8R Fault Code E-33: Complete Diagnostic Guide

What is Komatsu PC850-8R Fault Code E-33?

Fault Code E-33 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically relates to the temperature monitoring system that protects the Komatsu SAA6D170E-5 engine from overheating damage.

The coolant temperature sensor provides critical data to the ECM, which uses this information to adjust fuel injection timing, control engine speed, and activate warning systems. On the PC850-8R, this sensor is essential for maintaining optimal operating temperatures in demanding excavation conditions. When E-33 triggers, the machine's performance and longevity are at risk, as the ECM cannot properly regulate engine functions without accurate temperature data.

Common Symptoms

When Code E-33 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with accompanying audible alarm
• Engine derate mode activated, limiting maximum RPM and hydraulic power output
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Difficulty starting in cold conditions or excessive white smoke during warm-up

Potential Causes

The most common technical reasons for E-33 on used PC850-8R excavators include:

• Coolant temperature sensor failure due to age-related degradation or thermal cycling damage
• Wiring harness damage at known rub points near the engine block mounting brackets
• Corroded or loose electrical connectors at the sensor or ECM interface
• ECM internal fault affecting the temperature monitoring circuit
• Contaminated coolant causing sensor element fouling or incorrect readings
• Short circuits in the sensor wiring caused by insulation breakdown from heat exposure

How to Troubleshoot and Fix Code E-33

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block's coolant passage. Check for physical damage, coolant leaks, or corrosion on the connector terminals. On used excavators, examine the entire wiring harness from sensor to ECM for chafing, especially where it contacts frame members or passes through grommets.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (typically 2,000-3,000 ohms at 20°C for Komatsu sensors). Compare readings against manufacturer specifications. Check for continuity in the wiring harness and verify ground integrity. Inspect for voltage drops exceeding 0.2V, which indicate connection problems.

Step 3: Component Replacement and Verification If sensor resistance is out of specification or wiring shows damage, replace the faulty component using genuine Komatsu parts (part number 7861-93-3320 or equivalent). After replacement, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool. Perform a test cycle monitoring live coolant temperature data to confirm proper operation.

Critical for Used Machines: Before replacing expensive components, thoroughly clean all connector pins with electrical contact cleaner and apply dielectric grease to prevent future corrosion—a common issue in high-hour excavators.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and seek professional assistance from certified technicians for complex repairs.