Komatsu PC200-10 Fault Code CA691: Expert Guide

What is Komatsu PC200-10 Fault Code CA691?

Fault Code CA691 indicates a communication error between the Engine Controller (ECM) and the Hydraulic Pump Controller (HPC) on the Komatsu PC200-10 excavator. This CAN bus communication failure prevents proper coordination between engine power output and hydraulic demand, disrupting the machine's integrated control system.

This code specifically triggers when the ECM fails to receive valid data packets from the HPC within the programmed timeout period (typically 500 milliseconds). The PC200-10's advanced load-sensing hydraulic system relies on constant ECM-HPC communication to optimize fuel efficiency and hydraulic performance. When this communication breaks down, the machine cannot properly match engine speed to hydraulic requirements, severely impacting operational efficiency and potentially causing component damage.

For used excavators, this fault is particularly critical because the integrated control system is fundamental to the PC200-10's performance advantages over older models.

Common Symptoms

• Machine enters derate mode, limiting engine RPM to approximately 1,500 RPM to protect components
• Hydraulic response becomes sluggish or erratic, with delayed bucket or arm movements
• Warning light illuminates on the instrument cluster, often accompanied by audible alarm
• Diagnostic monitor displays CA691 with possible simultaneous codes related to hydraulic pressure
• Inconsistent engine speed during loaded operations, with sudden RPM drops under hydraulic demand

Potential Causes

CAN Bus Wiring Issues: The CAN-H and CAN-L communication wires between the ECM and HPC are susceptible to damage on used machines, particularly where harnesses route near the swing post or along the boom base. Chafing against metal edges is common after 5,000+ operating hours.

HPC Controller Failure: The hydraulic pump controller's internal circuit boards can develop cold solder joints or capacitor failures, especially in machines operated in high-temperature environments or with contaminated hydraulic oil causing overheating.

ECM Software Corruption: Voltage spikes from jump-starting or electrical system issues can corrupt ECM programming, disrupting proper CAN protocol timing.

Corroded Connectors: The 9-pin connector at the HPC and the ECM's communication harness connector (located behind the operator's seat) are prone to moisture intrusion on older units, causing intermittent resistance that disrupts data transmission.

Terminating Resistor Failure: The CAN bus network requires proper 120-ohm terminating resistors; one resistor is typically integrated into the HPC on PC200-10 models.

How to Troubleshoot and Fix Code CA691

Step 1: Verify Communication Circuit Integrity

Using a digital multimeter, measure resistance between CAN-H and CAN-L terminals with all controllers connected and ignition off. You should read approximately 60 ohms (two 120-ohm resistors in parallel). A reading significantly higher indicates an open circuit or failed terminating resistor. Disconnect the HPC connector and measure again—resistance should increase to 120 ohms if the HPC's internal resistor is functioning.

Step 2: Inspect Harness and Connectors

Physically trace the CAN bus harness from the ECM (located right-side of engine compartment) to the HPC (mounted on the hydraulic pump). On used excavators, pay special attention to wear points where the harness passes through the bulkhead near the swing bearing and where it clamps to the pump mounting bracket. Look for insulation wear, exposed copper, or harness discoloration indicating previous shorting. Remove both connectors and inspect pins for corrosion or bent terminals—clean with electrical contact cleaner and apply dielectric grease.

Step 3: Perform Voltage Tests

With ignition on (engine off), backprobe the CAN-H wire at the HPC connector—you should measure approximately 2.5V to ground. The CAN-L wire should also read approximately 2.5V (CAN bus at idle/recessive state). During active communication (engine running), these voltages should oscillate. If voltages are absent, suspect ECM failure or power supply issues to the communication circuit.

Step 4: Check Software and Perform Relearn

Connect Komatsu KOMTRAX diagnostic software or compatible Komatsu diagnostic tool to verify ECM and HPC software versions are compatible and not corrupted. Perform a controller relearn procedure to re-establish communication protocols—this often resolves intermittent CA691 codes after battery disconnection or electrical work on used machines.

Step 5: Test HPC Functionality

If communication circuit tests pass but the code persists, swap the HPC with a known-good unit (if available) or send for bench testing. HPC failures manifest differently than wiring issues—the code will typically be constant rather than intermittent. Before replacing expensive controllers on used equipment, verify all ground connections at both the ECM and HPC are clean and tight, as poor grounds cause bizarre communication errors.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu PC200-10 service manual and follow manufacturer-specific procedures. Complex electrical diagnostics should be performed by certified Komatsu technicians with proper diagnostic equipment. Improper troubleshooting can cause additional system damage.