Komatsu PC850SE-8R Fault Code E-6: Complete Diagnostic Guide

What is Komatsu PC850SE-8R Fault Code E-6?

Fault Code E-6 on the Komatsu PC850SE-8R indicates an Engine Controller (ECM) communication error or malfunction in the engine control system's primary circuit. This code specifically relates to a breakdown in data transmission between the Engine Control Module (ECM) and other critical electronic components within the machine's monitoring network.

The E-6 code represents a serious diagnostic concern because the ECM serves as the central processing unit for engine management, controlling fuel injection timing, emissions systems, and performance parameters. When communication fails, the excavator's ability to optimize engine performance and protect against damage becomes severely compromised. For the PC850SE-8R's high-output diesel engine, maintaining proper ECM function is essential for fuel efficiency, emissions compliance, and preventing costly engine damage.

Common Symptoms

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

• Engine warning light illuminated on the main instrument panel, often accompanied by audible alarms
• Reduced engine power or derate mode, limiting machine performance to protect the engine
• Erratic engine behavior, including irregular idle, unexpected shutdowns, or difficulty starting
• Loss of diagnostic display functions, with the monitor showing incomplete or frozen data
• Intermittent electrical issues affecting other systems controlled by the ECM network

Potential Causes

The most common technical causes for Code E-6 on used PC850SE-8R excavators include:

• ECM power supply failure due to corroded or loose connections at the main power harness
• Damaged wiring harness between the ECM and engine sensors, particularly at known rub points near the engine mounting brackets
• Failed ECM internal components, especially in high-hour machines with exposure to vibration and heat cycles
• Corroded ground connections affecting the ECM's reference voltage and communication protocols
• Water intrusion into the ECM housing or connector pins, common in machines operated in wet conditions
• Faulty CAN bus termination resistors or damaged communication wiring in the data network

How to Troubleshoot and Fix Code E-6

Step 1: Visual Inspection Begin with a thorough inspection of the ECM and its wiring harness. Check all connector pins for corrosion, bent terminals, or moisture. On used excavators, pay special attention to harness routing near the engine block where heat and vibration cause insulation breakdown.

Step 2: Power Supply Verification Using a digital multimeter, verify the ECM receives proper voltage (typically 24V DC). Check the main power supply wire and ground connections. Measure resistance between the ECM ground and chassis ground—it should read less than 1 ohm. Clean and tighten all ground points.

Step 3: Communication Network Testing With Komatsu diagnostic software (KOMTRAX Plus) or compatible scan tool, attempt to establish communication with the ECM. If communication is intermittent, inspect the CAN bus wiring for shorts or opens. Check termination resistors at network endpoints (should measure approximately 60 ohms across CAN-H and CAN-L).

Step 4: ECM Replacement Consideration If power supply and wiring check out, the ECM itself may have failed. Before replacement, verify the part number matches your specific engine serial number. For used machines, consider having the existing ECM bench-tested before purchasing a replacement, as these units are expensive.

Critical for Used Equipment: Always inspect connector seals and apply dielectric grease to prevent future corrosion. Check service history for previous electrical repairs that may indicate recurring issues.

---

Disclaimer: This guide provides general diagnostic information. Complex electrical issues should be diagnosed by qualified technicians with proper Komatsu diagnostic equipment. Always consult the official service manual for your specific machine serial number.