Komatsu PC750LC-7 Fault Code E980: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code E980?

Fault Code E980 indicates a communication error between the Engine Control Module (ECM) and the Hydraulic Control Module (HCM) on the Komatsu PC750LC-7 excavator. This code specifically signals that the CAN bus communication network has experienced an interruption or data transmission failure between these two critical control systems.

The PC750LC-7 relies on continuous data exchange between the ECM and HCM to optimize engine performance relative to hydraulic demand. When this communication link fails, the machine cannot properly coordinate power delivery with hydraulic functions, severely impacting operational efficiency. This is particularly critical in the PC750LC-7, where the integrated control system manages fuel efficiency and hydraulic response simultaneously.

Common Symptoms

When Code E980 is active, operators typically experience:

• Warning light illumination on the monitor panel with reduced machine responsiveness
• Hydraulic system derate or sluggish boom, arm, and bucket movements
• Engine power limitation preventing the machine from reaching full RPM under load
• Intermittent loss of auxiliary hydraulic functions including attachments
• Error messages displayed on the multi-function monitor indicating communication faults

Potential Causes

The most common technical causes for E980 on used PC750LC-7 excavators include:

• CAN bus wiring harness damage from rubbing against the frame near the engine compartment or along the main boom pivot point
• Corroded or loose connector pins at the ECM or HCM connection points, especially in machines exposed to moisture
• Failed termination resistors on the CAN bus network (120-ohm resistors at network endpoints)
• ECM or HCM internal failure due to voltage spikes or age-related component degradation
• Damaged shielding on CAN bus cables causing electromagnetic interference
• Low battery voltage or poor ground connections affecting module power supply

How to Troubleshoot and Fix Code E980

Step 1: Visual Inspection Begin by inspecting all wiring harnesses between the ECM (located behind the operator cab) and HCM (mounted near the hydraulic pump). Look for chafing, cuts, or pinch points where harnesses route through the swing bearing area. On used excavators, check for previous repair attempts using non-shielded wire or improper splices.

Step 2: Connector Examination Disconnect and inspect the CAN bus connectors at both modules. Clean any corrosion using electrical contact cleaner and verify all pins are straight and making proper contact. Check connector seals for deterioration—a common issue on machines with 5,000+ operating hours.

Step 3: Electrical Testing Using a digital multimeter, measure CAN High and CAN Low voltage at the ECM connector with the key on, engine off. You should read approximately 2.5V on each line at rest. Check for 120-ohm resistance between CAN High and CAN Low with modules disconnected—this confirms termination resistors are intact.

Step 4: Advanced Diagnostics Connect Komatsu KOMTRAX or compatible diagnostic software to monitor real-time CAN bus traffic. This will identify whether one module is failing to transmit. For used machines, perform a wiggle test on harnesses while monitoring communication to locate intermittent breaks.

Step 5: Component Replacement If wiring and connections test properly, the issue likely resides in the ECM or HCM. Before replacing expensive modules on used equipment, verify battery voltage remains above 24V during cranking and check all ground straps for resistance below 0.5 ohms.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues. Improper repairs may cause additional system damage.