Komatsu PC750SE-7 Fault Code E920: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E920?

Fault Code E920 indicates a communication error between the Engine Control Module (ECM) and the Hydraulic Control Module (HCM) on the Komatsu PC750SE-7 excavator. This code specifically signals that the CAN bus communication network has experienced an interruption, timeout, or data transmission failure between these two critical control systems.

The PC750SE-7 relies on continuous data exchange between the ECM and HCM to optimize engine performance, hydraulic flow, and fuel efficiency. When communication breaks down, the machine cannot properly coordinate engine output with hydraulic demand, potentially causing reduced productivity and increased fuel consumption. This fault is particularly critical because it affects the integrated control system that makes modern excavators efficient.

Common Symptoms

When Code E920 is active, operators typically experience:

• Warning light illumination on the monitor panel, often accompanied by a communication error message
• Reduced hydraulic response or sluggish boom/arm movements due to improper engine-hydraulic coordination
• Engine derate mode where maximum RPM is limited to protect the powertrain
• Intermittent loss of monitor display functions, including fuel consumption or hydraulic temperature readings
• Erratic engine behavior during simultaneous multi-function operations (e.g., boom lift while slewing)

Potential Causes

The most common technical causes for E920 on used PC750SE-7 excavators include:

• CAN bus wiring harness damage from rubbing against the frame near the engine mounting points or hydraulic pump area
• Corroded or loose connector pins at the ECM or HCM connection points, especially on machines operating in wet or coastal environments
• Failed termination resistors on the CAN bus network (typically 120-ohm resistors at network endpoints)
• ECM or HCM internal failure, though less common than wiring issues
• Voltage supply problems to either control module due to failing alternator or battery connections
• Water intrusion into controller housings from damaged seals or improper maintenance

How to Troubleshoot and Fix Code E920

Step 1: Visual Inspection Begin by inspecting the wiring harness between the ECM (located behind the operator cab) and the HCM (mounted near the hydraulic pumps). On used excavators, check for harness wear at known rub points, particularly where cables pass through bulkheads or near vibrating components. Examine all connector pins for corrosion, bent terminals, or moisture.

Step 2: Electrical Testing Using a digital multimeter, verify power supply to both modules (typically 24V DC). Check CAN-High and CAN-Low wire continuity between ECM and HCM connectors. Measure termination resistance across the CAN bus—you should read approximately 60 ohms with both modules connected (two 120-ohm resistors in parallel).

Step 3: Advanced Diagnostics Connect Komatsu KOMTRAX diagnostic software or compatible scan tool to monitor real-time CAN bus traffic. Check for intermittent dropouts or error frames. If wiring tests pass, suspect internal module failure—swap modules with known-good units if available for confirmation.

Step 4: Repair and Verification Replace damaged harnesses, clean corroded connectors with electrical contact cleaner, and apply dielectric grease to prevent future corrosion. After repairs, clear codes and operate the machine through full work cycles to ensure stable communication.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnostic assistance for complex electrical issues.