What is Komatsu PC240LC-10 Fault Code CA428?

Fault Code CA428 indicates a malfunction in the Engine Speed Sensor Circuit, specifically detecting an abnormal signal or complete loss of signal from the crankshaft position sensor to the Engine Control Module (ECM). This diagnostic trouble code (DTC) is triggered when the ECM fails to receive proper rpm data from the engine speed sensor, which is critical for fuel injection timing, engine speed regulation, and overall engine management.

On the Komatsu PC240LC-10 equipped with the SAA6D107E-1 engine, this sensor provides essential feedback for the common rail fuel injection system. Without accurate engine speed data, the ECM cannot properly calculate fuel delivery, potentially causing the machine to enter a protective derate mode or prevent starting altogether. This code is particularly critical because engine speed monitoring directly affects power output, emissions control, and prevents potential engine damage from over-revving.

Common Symptoms

• Engine cranks but fails to start, or starts then immediately shuts down
• Amber or red engine warning light illuminated on the instrument cluster
• Significant power loss or derate mode where the engine limits maximum rpm to 1200-1500 range
• Erratic engine idle or rough running conditions with inconsistent throttle response
• Diagnostic display showing CA428 when accessed through the monitor panel

Potential Causes

The most frequent causes of CA428 on used PC240LC-10 excavators include:

• Failed crankshaft position sensor due to heat exposure or internal component breakdown (common after 6,000+ hours)
• Damaged sensor wiring harness from rubbing against the engine block near the flywheel housing—a known wear point on this model
• Corroded or loose connector pins at the sensor plug or ECM connection, especially in machines operated in wet or marine environments
• Contaminated sensor face from oil leaks or metallic debris accumulation on the magnetic pickup
• ECM internal fault (less common) affecting the speed sensor input circuit
• Broken or damaged flywheel teeth causing irregular signal generation

How to Troubleshoot and Fix Code CA428

Step 1: Visual Inspection Locate the engine speed sensor on the left side of the engine block near the flywheel housing. Inspect the sensor, connector, and wiring harness for obvious damage, oil contamination, or corrosion. On used excavators, carefully check where the harness routes along the engine—rubbing against the block is a frequent failure point on older PC240LC models.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to check sensor resistance. The crankshaft position sensor should read approximately 190-250 ohms at room temperature. Also measure resistance in the wiring harness from the sensor connector back to the ECM connector E2 (pins should show continuity with less than 5 ohms resistance). Check for short circuits to ground (should show infinite resistance).

Step 3: Signal Testing Using Komatsu KOMTRAX diagnostic software or an oscilloscope, monitor the AC voltage signal from the sensor while cranking the engine. You should see a waveform with voltage varying between 0.5-3.0V AC. An absent or erratic signal confirms sensor failure.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu part number 7861-93-1651 or equivalent OEM sensor. Clean the mounting surface thoroughly and ensure proper air gap (typically self-adjusting). For used machines, always replace the connector pigtail if any corrosion is present—this prevents recurring failures.

Step 5: Clear Code and Verify After replacement, clear the fault code using diagnostic software and operate the machine through a full duty cycle to confirm proper repair.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number, and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-pressure fuel systems.