What is Komatsu PC210LC-7 Fault Code E256?

Komatsu PC210LC-7 Fault Code E256 indicates a malfunction in the engine controller's communication circuit with the pump control system, specifically relating to abnormal signal detection between the Engine Control Module (ECM) and the hydraulic pump controller. This code triggers when the ECM detects inconsistent or missing data packets from the pump flow control solenoid feedback circuit, disrupting the coordinated engine-pump matching system that's critical for the PC210LC-7's fuel efficiency and performance.

This fault is particularly critical on the PC210LC-7 because this generation of Komatsu excavators relies on CLSS (Closed-Center Load-Sensing System) technology, where precise ECM-to-pump communication ensures optimal hydraulic flow matches engine output. When E256 appears, this coordination breaks down, potentially causing excessive fuel consumption and reduced digging performance.

Common Symptoms

• Machine derate mode – Engine power limited to approximately 70-80% of rated output, with noticeable sluggishness in boom and bucket operations
• Yellow warning lamp illuminated on the monitor panel, often accompanied by intermittent beeping
• Erratic hydraulic response – Inconsistent pump flow causing jerky movements during combined functions (swing + boom operations)
• Increased engine RPM without corresponding increase in hydraulic speed, indicating loss of electronic load-sensing calibration
• Diagnostic monitor displays "Engine-Pump Communication Error" or similar message on machines equipped with advanced display panels

Potential Causes

The most frequent causes of E256 on used PC210LC-7 excavators include:

• Damaged wiring harness between ECM and pump controller, particularly at the routing point near the hydraulic pump mounting bracket where vibration causes wire chafing
• Corroded connector pins on the 18-pin pump controller connector (C-203), especially common in machines operated in coastal or high-humidity environments
• Failed pump control solenoid feedback sensor – typically from age-related internal coil degradation after 8,000+ operating hours
• ECM internal communication board failure – less common but documented in PC210LC-7 units manufactured between 2004-2006
• Voltage supply issues from the main relay circuit providing power to the pump controller (should maintain steady 24V DC)

How to Troubleshoot and Fix Code E256

Step 1: Visual Inspection and Voltage Verification Begin by inspecting the main wiring harness running from the ECM (located behind the operator's seat) to the hydraulic pump controller (mounted on the main pump). Look for obvious wire damage, particularly where the harness passes through metal grommets near the pump. Using a digital multimeter, verify the pump controller receives stable 24V DC at connector C-203, pin 1 (power supply) and pin 9 (ground).

Step 2: Connector and Communication Circuit Testing Disconnect connector C-203 at the pump controller and inspect for corrosion, bent pins, or moisture intrusion – extremely common on used excavators. Clean contacts with electrical contact cleaner and apply dielectric grease. With the connector disconnected and ignition on (engine off), use Komatsu KOMTRAX diagnostic software or compatible scan tool to monitor communication attempts. Check resistance between ECM pins and pump controller pins per Komatsu specifications (typically 120 Ω across the CAN communication lines).

Step 3: Component Testing and Replacement If wiring and voltage check out, test the pump flow control solenoid feedback circuit. With the engine running at low idle, measure the AC voltage signal from the feedback sensor (should show 0.5-4.5V AC fluctuation). On used excavators, don't immediately replace the expensive pump controller – first swap the ECM with a known-good unit if available, as ECM communication board failures mimic pump controller issues. Replace components only after confirming the fault through isolation testing.

Critical for Used Machines: Before ordering parts, check service history for previous hydraulic system work – improper pump replacement or ECM reprogramming can cause phantom E256 codes that clear after proper calibration using Komatsu's PLUS+1 software.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC210LC-7 Service Manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may void warranties or cause additional damage.