What is Komatsu PC120-6 Fault Code E316?

Komatsu PC120-6 fault code E316 indicates a malfunction in the engine throttle control system — specifically, an abnormality detected in the throttle volume (potentiometer) signal circuit.

This code is triggered when the Engine Control Module (ECM) receives a signal from the throttle position sensor (fuel control dial) that falls outside the specified voltage range. On the PC120-6, this dial directly governs engine RPM through the fuel injection pump actuator, making accurate signal transmission critical for engine response and output control.

A faulty throttle signal can prevent the machine from reaching full power, which directly impacts productivity and can mask deeper drivetrain issues.

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Common Symptoms

When E316 is active on a Komatsu PC120-6, operators typically report:

• Engine RPM will not increase beyond low idle regardless of dial position
• Warning lamp illuminates on the monitor panel with engine derating
• Erratic or hunting engine speed — RPM fluctuates unpredictably during operation
• Loss of hydraulic power due to insufficient engine output
• Machine enters limp mode, severely limiting work performance

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Potential Causes

The most common technical root causes for E316 on this model include:

• Worn or failed throttle potentiometer — the resistive track degrades with age and heavy use
• Damaged wiring harness between the throttle dial and ECM — a known friction point exists where the cab harness passes near the door hinge on this chassis
• Corroded or loose connector pins at the throttle sensor plug or the ECM connector block
• Open or short circuit in the signal wire (Pin A, throttle signal line)
• Faulty ECM — less common, but possible on high-hour machines with moisture ingress history

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How to Troubleshoot and Fix Code E316

Step 1 — Visual Inspection First Before touching any components, inspect the throttle dial harness and its routing through the cab. On used PC120-6 units, pay close attention to harness abrasion points near the cab door hinge and floor penetration grommet. Look for cracked insulation, chafing, or corrosion on the 3-pin connector at the throttle potentiometer.

Step 2 — Measure Supply and Signal Voltage Using a digital multimeter, backprobe the throttle sensor connector with the key ON (engine OFF). Verify:

• Supply voltage (Pin C to ground): should read 5V DC ± 0.5V
• Signal voltage (Pin A to ground): should range from approximately 0.5V (low idle) to 4.5V (full throttle) as the dial rotates

If supply voltage is absent or signal voltage is stuck or out of range, the fault lies in the circuit or sensor itself.

Step 3 — Check Resistance of the Potentiometer Disconnect the sensor and measure resistance across the potentiometer terminals. The full sweep should produce a smooth, linear change in resistance. Any dead spots, open readings, or sudden jumps indicate a failed throttle potentiometer requiring replacement.

Step 4 — Inspect ECM Connector If wiring and sensor test normal, inspect the ECM harness connector for bent pins, moisture damage, or corrosion. Use Komatsu KOMTRAX or PC120-6 compatible diagnostic software (such as Komatsu INSITE or a compatible aftermarket scan tool) to verify live data and confirm the ECM is reading the corrected signal after repairs.

Step 5 — Clear Code and Verify After any repair, clear stored codes via the diagnostic tool and perform a full throttle sweep test to confirm the fault does not return.

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Disclaimer: This guide is intended for qualified heavy diesel mechanics and experienced equipment technicians. Diagnostic procedures on Komatsu machinery should be performed following the manufacturer's official service manual specifications. If you are uncertain about any step, consult a certified Komatsu dealer or licensed heavy equipment technician before proceeding. Improper repairs may cause further damage or create safety hazards.