Komatsu PC120LC-6 Fault Code E207: Complete Diagnostic Guide

What is Komatsu PC120LC-6 Fault Code E207?

Fault code E207 on the Komatsu PC120LC-6 indicates a malfunction in the engine speed sensor circuit, specifically detecting an abnormal signal or loss of signal from the engine revolution sensor.

This code is generated by the ECM (Engine Control Module) when it fails to receive valid RPM data from the magnetic pickup sensor mounted on the flywheel housing. The engine speed sensor is critical for fuel injection timing, governor control, and overall engine management on the 6D95L diesel engine used in this model.

Without accurate engine speed data, the ECM cannot properly regulate fuel delivery, leading to poor performance and potential engine protection activation.

Common Symptoms

• Engine runs rough or stalls unexpectedly during operation
• Erratic idle speed that fluctuates without throttle input
• Reduced engine power with sluggish hydraulic response
• Check Engine warning lamp illuminated on the monitor panel
• Difficulty starting or extended cranking before ignition

Potential Causes

The most common causes for E207 on used PC120LC-6 units include:

• Damaged engine speed sensor due to heat exposure or age-related failure
• Corroded or loose connector pins at the sensor or ECM harness junction
• Chafed wiring harness near the flywheel housing where vibration causes abrasion
• Contaminated sensor tip with metal debris or oil buildup affecting magnetic signal
• Improper sensor air gap between pickup and flywheel ring gear teeth
• ECM ground issues causing signal interference

How to Troubleshoot and Fix Code E207

Step 1: Visual Inspection Locate the engine speed sensor on the right side of the flywheel housing. Inspect the wiring harness for chafing, cuts, or heat damage. On used excavators, pay particular attention to areas where the harness contacts metal brackets or exhaust components. Check the connector for corrosion, bent pins, or moisture intrusion.

Step 2: Sensor Testing Disconnect the sensor connector and use a multimeter to measure resistance across the sensor terminals. The specification is typically 190-250 ohms at room temperature. Values outside this range indicate sensor failure. Also verify continuity from the sensor connector to the ECM pins to rule out open circuits.

Step 3: Air Gap Verification Using a feeler gauge, confirm the sensor-to-flywheel gap is within 0.5-1.5mm. Excessive gap from mounting bolt looseness is common on high-hour machines.

Step 4: Signal Verification With the sensor reconnected, use an oscilloscope or Komatsu diagnostic tool to verify AC voltage output during cranking. A healthy sensor produces 1-5V AC pulses proportional to engine speed.

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Disclaimer: This guide is for informational purposes. Complex electrical diagnostics should be performed by qualified technicians using proper safety procedures and manufacturer-approved service literature.