What is Komatsu PC1250-11R Fault Code CB697?

Fault Code CB697 indicates a communication error or malfunction in the engine control system's CAN (Controller Area Network) bus, specifically related to a timeout or lost message between the Engine Control Module (ECM) and another critical control unit. This code typically signals that the ECM is not receiving expected data packets from a connected controller within the prescribed time interval, disrupting coordinated machine operations.

On the Komatsu PC1250-11R, this large mining-class excavator relies on seamless CAN bus communication between multiple controllers including the engine ECM, pump controller, and monitoring systems. When CB697 activates, it compromises the machine's ability to optimize hydraulic pump output, fuel injection timing, and emission controls based on real-time load demands. This fault is critical because the PC1250-11R's advanced load-sensing hydraulics and integrated machine control depend on millisecond-level data exchange between modules.

Common Symptoms

• Warning light illumination on the operator display panel with reduced engine power or derate mode activation
• Intermittent or complete loss of monitor display functions, including fuel consumption data, diagnostic readouts, or system temperatures
• Erratic hydraulic response or inability to achieve full boom/bucket speed under load due to pump controller miscommunication
• Engine stalling or rough idling when multiple hydraulic functions are operated simultaneously
• Stored fault codes that appear and disappear without consistent pattern, indicating intermittent connection issues

Potential Causes

The most common technical causes for CB697 on used PC1250-11R excavators include:

• Corroded or loose CAN bus connectors at the ECM harness junction, particularly the 38-pin main connector which is exposed to vibration
• Damaged CAN bus wiring along known rub points near the engine mounting brackets or where harnesses pass through the revolving frame junction
• Failed terminating resistor (120-ohm) at either end of the CAN network backbone, causing signal reflection and data corruption
• ECM internal failure or corrupted firmware requiring reflashing with Komatsu diagnostic software
• Voltage irregularities from failing alternator or weak batteries causing ECM brownouts during high electrical load periods
• Aftermarket component interference from non-OEM monitoring systems improperly connected to the CAN network

How to Troubleshoot and Fix Code CB697

Step 1: Visual Inspection of CAN Harness Begin by thoroughly inspecting all CAN bus wiring (typically twisted orange/green pair) from the ECM through junction boxes to connected controllers. On used excavators, focus on harness routing near the turret bearing where flexing causes insulation breakdown. Check all connectors for corrosion, bent pins, or moisture intrusion—clean with electrical contact cleaner and apply dielectric grease.

Step 2: Verify CAN Bus Integrity Using a digital multimeter, measure resistance between CAN-High and CAN-Low terminals at the ECM connector (engine off, harness disconnected). You should read approximately 60 ohms, indicating both 120-ohm terminating resistors are present and functional. Deviation suggests open circuit, short, or missing terminator.

Step 3: Check Power Supply and Grounds Verify the ECM receives stable 24V DC power (key on, engine off) and that all ground connections show less than 0.1 ohms resistance to chassis. Weak grounds are particularly problematic on high-hour machines with corroded frame connections.

Step 4: Diagnostic Software Analysis Connect Komatsu KOMTRAX or PC-based diagnostic software to read live CAN bus traffic and identify which specific controller is timing out. This pinpoints whether the issue lies with pump controller, monitor, or another module. Check for available ECM software updates that address known communication bugs.

Step 5: Component Replacement If diagnostics isolate a failed module, replace the terminating resistor (simple inline component), repair damaged harness sections with proper twisted-pair shielded cable, or replace the faulty controller. For used machines, always verify replacement parts match the machine's serial number range to ensure compatibility.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu PC1250-11R service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs to CAN bus systems can cause additional controller damage.