Komatsu PC850SE-8R Fault Code E-29: Complete Diagnostic Guide

What is Komatsu PC850SE-8R Fault Code E-29?

Fault Code E-29 on the Komatsu PC850SE-8R 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 engine from overheating damage.

The coolant temperature sensor provides critical data to the ECM, which uses this information to regulate fuel injection timing, engine speed limits, and activate warning systems. On the PC850SE-8R's high-output diesel engine, maintaining proper temperature monitoring is essential to prevent catastrophic engine damage, as this machine operates under extreme loads in demanding applications. When E-29 triggers, the ECM may implement protective measures that limit machine performance.

Common Symptoms

When Code E-29 is active, operators typically experience:

• Engine warning light or malfunction indicator illuminated on the monitor panel
• Engine derate mode activated, limiting maximum RPM and hydraulic power output
• Inaccurate coolant temperature readings displayed (showing extremely high or low values)
• Cooling fan running continuously at maximum speed regardless of actual engine temperature
• Difficulty starting in cold conditions or excessive warm-up times

Potential Causes

The most common technical causes for E-29 on used PC850SE-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 or along the chassis rail
• Corroded or loose electrical connectors at the sensor or ECM interface (common in machines exposed to moisture)
• ECM internal circuit failure affecting the temperature input channel
• Damaged sensor mounting threads causing poor thermal contact with coolant passages
• Contaminated coolant causing sensor element fouling or scaling

How to Troubleshoot and Fix Code E-29

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically near the thermostat housing). 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 bulkheads.

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 68°F, but verify against Komatsu specifications). Test harness continuity from the sensor connector to the ECM pins. Check for short circuits to ground or power by measuring resistance between each wire and chassis ground (should read infinite resistance).

Step 3: Live Data Analysis Connect Komatsu diagnostic software (KOMTRAX or compatible scan tool) to monitor real-time coolant temperature values. Compare displayed temperature against actual engine temperature using an infrared thermometer. A variance greater than 10°F indicates sensor or circuit problems.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu coolant temperature sensor (part-specific to PC850SE-8R). Clean mounting threads and apply appropriate thread sealant. For used machines, consider replacing the connector pigtail simultaneously, as corrosion often affects both components. Clear codes using diagnostic software and verify repair through a complete heat cycle.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.