Caterpillar Excavator Fault Code 654-6: Meaning, Symptoms & Fix

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What is Caterpillar Fault Code 654-6?

Caterpillar Fault Code 654-6 indicates a Fuel Injector Cylinder #6 — Current Above Normal condition. This means the ECM (Engine Control Module) has detected that the current flowing through the #6 fuel injector solenoid circuit is exceeding the manufacturer's acceptable threshold.

In Caterpillar's diagnostic framework, the "-6" suffix specifically identifies an overcurrent fault on that circuit. This is a critical code because excessive current can damage the injector driver circuit inside the ECM, lead to injector failure, and cause severe engine performance degradation if left unresolved.

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Common Symptoms

When Fault Code 654-6 is active, operators typically experience:

• Rough engine idle or misfiring, particularly noticeable at low RPM
• Active Check Engine or Diagnostic Warning Lamp illuminated on the operator display
• Engine power derate as the ECM enters a protective reduced-power mode
• Excessive black or white exhaust smoke from incomplete combustion in cylinder #6
• Increased fuel consumption with reduced hydraulic response during operation

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Potential Causes

The most likely technical causes for this fault include:

• Shorted fuel injector solenoid — internal winding failure causing a low-resistance short to ground
• Damaged wiring harness — particularly harness sections routed near the valve cover or exhaust manifold, common rub points on used Cat excavators
• Corroded or moisture-contaminated connectors at the injector or ECM harness plug
• Failed injector driver circuit inside the ECM itself, especially on high-hour machines
• Previous improper repairs — spliced wiring or wrong injector installation on used equipment with unknown service history

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How to Troubleshoot and Fix Code 654-6

Step 1 — Connect Diagnostic Software Use Caterpillar ET (Electronic Technician) software to confirm the active fault, check freeze frame data, and identify if the code is intermittent or continuous. Log injector trim codes and ECM parameters before clearing anything.

Step 2 — Inspect the Harness and Connectors Physically trace the #6 injector wiring harness from the injector to the ECM connector. On used excavators, pay close attention to harness chafing points near the rocker cover, heat shields, and any previous repair tape or splices. Look for corrosion, fretting, or moisture in all connectors.

Step 3 — Measure Injector Solenoid Resistance Disconnect the #6 injector connector and use a digital multimeter to measure solenoid resistance. A healthy Cat injector solenoid typically reads between 0.5–2.0 ohms depending on model. A reading near 0 ohms confirms an internal short — replace the injector.

Step 4 — Check for ECM Driver Damage If the harness and injector test good, measure voltage and resistance at the ECM harness connector pins for the #6 injector circuit. Abnormal readings here may indicate a damaged ECM injector driver requiring ECM replacement or professional reprogramming.

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Disclaimer: This guide is intended for informational purposes and as a general diagnostic reference. Always consult a certified Caterpillar dealer or licensed heavy equipment technician before performing repairs, particularly on ECM-related faults. Improper repairs can cause further component damage or void existing warranties.