Komatsu PC750SE-7 Fault Code E-6: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E-6?

Fault Code E-6 on the Komatsu PC750SE-7 indicates a malfunction in the engine controller (ECM) communication circuit or a critical sensor voltage abnormality within the engine management system. This code specifically relates to disrupted data transmission between the Engine Control Module (ECM) and other critical control systems, or an out-of-range voltage signal from key engine sensors.

This fault is particularly critical for the PC750SE-7 because it directly impacts the machine's ability to regulate fuel injection timing, turbocharger boost pressure, and emission controls. When communication breaks down, the excavator may enter a protective derate mode to prevent catastrophic engine damage, significantly reducing productivity on job sites.

Common Symptoms

When Code E-6 is active, operators typically experience:

• Engine warning light illuminated on the instrument cluster, often accompanied by audible alarms
• Reduced engine power or sudden derating, limiting maximum RPM to 1200-1500 range
• Erratic engine performance, including rough idling, hesitation during acceleration, or unexpected shutdowns
• Hydraulic system sluggishness due to insufficient engine power delivery
• Intermittent loss of dashboard display information or gauge malfunctions

Potential Causes

The most common technical causes for Code E-6 on used PC750SE-7 excavators include:

• Corroded or damaged wiring harness connectors at the ECM, particularly the main 48-pin connector prone to moisture intrusion
• Failed crankshaft position sensor or camshaft position sensor providing irregular voltage signals
• ECM power supply issues, including faulty main relay or degraded ground connections at chassis mounting points
• Harness chafing at known rub points near the engine firewall and along the right-hand frame rail
• ECM internal failure (less common but possible in high-hour machines exceeding 8,000 hours)
• Aftermarket component interference, especially non-OEM sensors installed during previous repairs

How to Troubleshoot and Fix Code E-6

Step 1: Initial Inspection Connect Komatsu KOMTRAX diagnostic software or a compatible scan tool to retrieve freeze-frame data. Document engine hours, operating conditions when the fault occurred, and any additional stored codes. Visually inspect the ECM harness for obvious damage, particularly at connector C1 behind the operator cab.

Step 2: Electrical Testing Using a digital multimeter, check ECM power supply voltage at pin 1 (should read 24V ±2V with key on). Test ground circuits at pins 24 and 48 for resistance below 0.5 ohms. Inspect sensor voltage supplies (typically 5V reference) at crankshaft and camshaft position sensors—out-of-spec readings indicate harness faults or ECM issues.

Step 3: Component Verification For used excavators, remove and inspect all harness connectors for green corrosion, bent pins, or moisture. Apply dielectric grease during reassembly. Test suspected sensors using resistance checks per Komatsu specifications (crankshaft sensor: 155-255 ohms at 20°C). Replace only confirmed failed components—avoid unnecessary parts replacement.

Step 4: Advanced Diagnostics If basic checks pass, perform CAN bus communication testing between ECM and other controllers. Check for software updates available for the ECM—Komatsu released several patches addressing communication errors in 2015-2017 production units.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750SE-7 service manual and consider professional technician assistance for complex electrical diagnostics. Improper repairs may void warranties or cause additional damage.