Komatsu PC240LC-10 Fault Code CA691: Technical Guide

What is Komatsu PC240LC-10 Fault Code CA691?

Fault Code CA691 indicates a malfunction in the exhaust temperature sensor circuit for the Diesel Particulate Filter (DPF) system. Specifically, this code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the DPF inlet or outlet temperature sensor, indicating either an open circuit, short circuit, or sensor reading outside normal operating parameters.

This fault is critical for the PC240LC-10's emission control system because accurate exhaust temperature monitoring is essential for proper DPF regeneration cycles. Without reliable temperature data, the ECM cannot effectively manage soot burn-off, potentially leading to DPF clogging, reduced engine performance, and violation of Tier 4 Final emission standards.

Common Symptoms

When Code CA691 is active, operators typically experience:

• Amber malfunction warning lamp illuminated on the instrument cluster
• DPF regeneration failure or inability to complete automatic regeneration cycles
• Reduced engine power (derate mode) after prolonged operation with active fault
• Increased exhaust backpressure warnings on the monitor display
• Excessive black smoke from the exhaust stack during load operations

Potential Causes

The most common technical causes for CA691 on used PC240LC-10 excavators include:

• Exhaust temperature sensor failure due to thermal cycling and carbon buildup on the probe tip
• Damaged wiring harness near the DPF canister where heat and vibration cause insulation breakdown
• Corroded connectors at the sensor interface, particularly on machines operated in wet or marine environments
• ECM voltage supply issues affecting the 5-volt reference circuit to the temperature sensor
• Previous aftertreatment system repairs with improperly routed or pinched sensor wiring

How to Troubleshoot and Fix Code CA691

Step 1: Visual Inspection Begin by inspecting the DPF exhaust temperature sensor and its wiring harness for obvious damage. On used excavators, check for heat-damaged insulation, connector corrosion (green oxidation), and wire chafing where the harness contacts the DPF housing or frame rails.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. A functional sensor typically reads 250-400 ohms at room temperature (consult Komatsu service manual for exact specifications). Also verify the ECM provides 5-volt reference voltage on the signal wire with ignition on, engine off.

Step 3: Circuit Continuity Check Test for continuity and shorts to ground throughout the sensor harness back to the ECM connector. Pay special attention to harness routing near high-heat zones and previous repair splices that may have failed.

Step 4: Sensor Replacement and Verification If electrical tests confirm sensor failure, replace with a genuine Komatsu temperature sensor (part-specific for Tier 4 systems). After installation, clear the fault code using Komatsu diagnostic software (KOMTRAX Plus) and perform a stationary DPF regeneration to verify proper operation.

For used equipment, always inspect the DPF differential pressure sensor simultaneously, as combined sensor failures often indicate systemic exhaust system issues requiring comprehensive aftertreatment service.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC240LC-10 service manual and consider professional diagnostics for complex emission system repairs. Improper DPF system repairs may violate emission regulations.