Komatsu PC800SE-7 Fault Code E957: Complete Diagnostic Guide

What is Komatsu PC800SE-7 Fault Code E957?

Fault Code E957 indicates a malfunction in the Engine Control Module (ECM) communication circuit, specifically related to a CAN (Controller Area Network) bus communication error or timeout between the engine controller and other critical machine systems.

This code triggers when the ECM fails to receive proper data signals from connected controllers within the specified time frame, typically affecting communication between the engine control system and the hydraulic or monitor control units. For the PC800SE-7, this is critical because the integrated control system relies on continuous data exchange to optimize engine performance, hydraulic response, and emission controls. Communication failures can result in reduced machine efficiency, improper fuel delivery, or complete system shutdowns.

Common Symptoms

When Code E957 is active, operators typically experience:

• Warning light illumination on the monitor panel, often accompanied by a "Check Engine" or communication error message
• Intermittent or complete loss of monitor display functions, including fuel gauge, temperature readings, or hour meter
• Engine derating or reduced power output as the ECM enters failsafe mode
• Erratic hydraulic performance due to disrupted communication between engine and hydraulic controllers
• Difficulty starting or unexpected engine shutdowns during operation

Potential Causes

The most common technical causes for E957 on used PC800SE-7 excavators include:

• Corroded or damaged CAN bus connectors at the ECM, monitor panel, or junction points (especially common in machines with 5,000+ hours)
• Harness chafing or wire breaks near the engine compartment where vibration and heat cause insulation deterioration
• Faulty ECM internal circuits or corrupted firmware requiring reprogramming
• Poor ground connections at the battery or ECM mounting points causing voltage fluctuations
• Water intrusion into sealed connectors from damaged grommets or failed seals
• Aftermarket component interference from non-OEM monitors or accessories disrupting CAN communication

How to Troubleshoot and Fix Code E957

Step 1: Visual Inspection Begin by thoroughly inspecting all wiring harnesses between the ECM (located behind the operator cab) and the monitor panel. Look for obvious damage, melted insulation, or connector corrosion. On used excavators, pay special attention to harness routing near the engine block where heat and vibration cause premature wear.

Step 2: Connector and Ground Testing Disconnect the main CAN bus connectors at the ECM and monitor controller. Clean all pins with electrical contact cleaner and inspect for bent terminals or green corrosion. Using a digital multimeter, verify ground continuity (should read less than 1 ohm resistance) between the ECM ground terminal and battery negative.

Step 3: CAN Bus Voltage Check With the ignition on (engine off), measure CAN-High and CAN-Low voltage at the ECM connector. You should read approximately 2.5V on CAN-High and 2.5V on CAN-Low at rest. During communication, these should fluctuate between 1.5-3.5V. No voltage or constant voltage indicates a circuit break or controller failure.

Step 4: Diagnostic Software Analysis Connect Komatsu KOMTRAX or compatible diagnostic software to retrieve detailed fault data, including which specific controller lost communication. This pinpoints whether the issue is ECM-related or originates from peripheral controllers.

Step 5: Component Replacement If wiring and connections test properly, the ECM itself may require replacement or reprogramming. For used machines, consider testing with a known-good ECM before purchasing new components, as these units exceed $2,000.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnosis for complex electrical issues, especially when dealing with expensive control modules.