Komatsu PC850-8R Fault Code E-29: Complete Diagnostic Guide

What is Komatsu PC850-8R Fault Code E-29?

Fault Code E-29 on the Komatsu PC850-8R 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 coolant temperature monitoring system, which is critical for preventing engine overheating and maintaining optimal operating temperatures.

The ECM continuously monitors signals from the coolant temperature sensor to regulate fuel injection timing, engine speed, and cooling fan operation. When the sensor provides readings outside the normal operating range (typically -40°C to 150°C), or when circuit voltage falls outside specified parameters (usually 0.5V to 4.5V), the system triggers E-29. For the PC850-8R's SAA6D170E-5 engine, proper temperature monitoring is essential for protecting this high-output powerplant from thermal damage and maintaining hydraulic system efficiency.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel with audible alarm
• Engine derate mode activated, limiting maximum RPM to protect components
• Cooling fan running continuously at high speed regardless of actual temperature
• Difficulty starting in cold conditions or rough idle during warm-up
• Inaccurate temperature gauge readings showing extreme high or low values

Potential Causes

The most common technical causes for E-29 on used PC850-8R excavators include:

• Coolant temperature sensor failure due to internal element degradation (common after 8,000+ hours)
• Wiring harness damage at known rub points near the engine block mounting brackets
• Corroded or loose connector pins at the sensor plug (especially in marine or coastal environments)
• ECM internal circuit failure affecting the temperature input channel
• Coolant contamination causing sensor element coating and false readings
• Ground circuit issues in the sensor return path to the ECM

How to Troubleshoot and Fix Code E-29

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for chafing, cuts, or heat damage. On used excavators, check for oil contamination on connectors and verify the connector lock is fully engaged. Look for coolant leaks that may indicate sensor seal failure.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At 20°C (68°F), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). Test circuit voltage at the harness connector with ignition on—you should see approximately 5V reference voltage from the ECM.

Step 3: Circuit Verification Check for continuity between the sensor connector and ECM pins (refer to wiring diagram). Measure ground circuit resistance, which should be less than 5 ohms. For used machines, inspect harness routing for wear points where insulation may have rubbed through, creating intermittent shorts.

Step 4: Component Replacement If sensor resistance is out of specification or circuit tests pass but the code persists, replace the coolant temperature sensor using genuine Komatsu parts. Clear codes using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor for code recurrence during 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 machine serial number and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic equipment.