Komatsu PC210LC-7 Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC210LC-7 Fault Code S-6?

Fault Code S-6 on the Komatsu PC210LC-7 indicates a malfunction in the fuel control dial (engine speed control) circuit. This code is triggered when the ECM (Engine Control Module) detects an abnormal voltage signal from the fuel dial potentiometer, which controls engine RPM settings.

The fuel control dial is critical for this excavator's performance because it directly regulates engine speed for different operating conditions. When the ECM cannot accurately read the operator's throttle input, the machine may default to fixed RPM settings or fail to respond to speed adjustments. On used excavators, this circuit is particularly vulnerable to wear from constant operator adjustment and environmental exposure to dust and vibration.

Common Symptoms

When Code S-6 is active on your PC210LC-7, you may experience:

• Engine runs at fixed RPM regardless of fuel dial position (typically stuck at idle or mid-range speed)
• S-6 error code displayed on the monitor panel with accompanying warning light
• Inconsistent or erratic engine speed response when adjusting the throttle dial
• Loss of engine deceleration function (auto-idle may not work properly)
• Reduced productivity due to inability to match engine speed to work requirements

Potential Causes

The most common technical causes for Code S-6 on used PC210LC-7 excavators include:

• Worn or damaged fuel dial potentiometer from repeated mechanical wear (common failure point after 5,000+ hours)
• Corroded or loose connector pins at the fuel dial harness connection behind the operator console
• Damaged wiring harness due to rubbing against the seat mounting bracket (known wear point on this model)
• Failed 5-volt reference circuit from the ECM to the potentiometer
• Water intrusion into the control dial assembly through worn cab seals
• ECM internal fault (rare, but possible on high-hour machines)

How to Troubleshoot and Fix Code S-6

Step 1: Visual Inspection Begin by accessing the fuel control dial assembly beneath the right armrest. Disconnect the 3-pin connector and inspect for corrosion, bent pins, or moisture. On used machines, this connector frequently shows green corrosion due to cab leaks. Clean contacts with electrical contact cleaner and apply dielectric grease.

Step 2: Test the Potentiometer Using a digital multimeter, measure resistance across the potentiometer terminals while rotating the dial. You should see smooth resistance change between approximately 0.5kΩ to 4.5kΩ. Any jumps, dead spots, or out-of-range readings indicate a failed potentiometer requiring replacement (Komatsu Part #: 7861-15-4110).

Step 3: Check Supply Voltage With ignition ON and connector attached, backprobe the signal wire (typically green/white) and measure voltage while moving the dial. You should see a smooth voltage sweep between 0.5V and 4.5V. Also verify the 5-volt reference supply from the ECM is present. Voltage outside this range or erratic readings suggest wiring issues or ECM problems.

Step 4: Inspect Harness for Damage Trace the wiring from the dial through the seat pivot area—this is a known harness rub point on PC210LC-7 models. Look for abraded insulation or broken wires. Repair any damage with proper 18-gauge wire and heat shrink, then reroute away from metal edges.

Step 5: Clear Code and Test After repairs, clear the fault code using Komatsu KOMTRAX diagnostic software or by disconnecting the battery for 30 seconds. Test operation through full throttle range and verify smooth engine response.

Disclaimer: This guide provides general troubleshooting procedures. For used excavators with complex electrical issues or persistent codes after these checks, consult a certified Komatsu technician or authorized service center for comprehensive diagnostics and calibration.