Caterpillar Fault Code 6335: Technical Guide

What is Caterpillar Fault Code 6335?

Caterpillar Fault Code 6335 indicates an "Injector Solenoid Circuit - Voltage Above Normal" or "High Side Driver Fault" in the engine's fuel injection system. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects abnormally high voltage in one or more fuel injector solenoid circuits, typically exceeding manufacturer-specified parameters.

This fault directly impacts the fuel delivery precision of electronically controlled injectors in Caterpillar diesel engines. When voltage spikes occur, the ECM cannot properly regulate fuel injection timing and duration, compromising engine performance, emissions compliance, and fuel efficiency. In modern Caterpillar engines with HEUI (Hydraulic Electronic Unit Injector) or common rail systems, maintaining proper injector voltage is critical for optimal combustion.

Common Symptoms

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the dashboard
• Engine derate mode activated, limiting maximum power output to protect components
• Rough idling or noticeable misfiring, particularly at low RPMs when precise fuel metering is crucial
• Hard starting conditions, especially during cold starts when injector response must be immediate
• Excessive black or white smoke from the exhaust due to improper fuel atomization

Potential Causes

The most common technical failures triggering Code 6335 in used Caterpillar excavators include:

• Damaged injector wiring harness - particularly at known rub points near the valve cover, cylinder head, or engine block where vibration causes insulation wear
• Faulty fuel injector solenoid with internal short circuits or coil degradation from heat cycles
• Corroded or moisture-contaminated connectors at the injector or ECM harness interface
• ECM internal driver circuit failure affecting the high-side transistor controlling injector power
• Chafed wiring contacting grounded metal surfaces, creating unintended voltage pathways
• Aftermarket harness repairs using incorrect gauge wire or improper shielding

How to Troubleshoot and Fix Code 6335

Step 1: Retrieve Active and Logged Codes Connect Caterpillar Electronic Technician (Cat ET) diagnostic software to identify which specific injector circuit is affected. Note whether the fault is active or intermittent, as this indicates continuous versus occasional voltage spikes.

Step 2: Perform Visual Harness Inspection With the engine off, thoroughly inspect the injector wiring harness for physical damage. On used excavators, focus on areas where the harness routes near hot exhaust components or moving parts. Check all deutsch connectors at each injector for corrosion, pin backing-out, or moisture intrusion—common issues in machines operating in wet conditions.

Step 3: Measure Injector Resistance Disconnect the suspect injector connector and use a digital multimeter (DMM) to measure solenoid coil resistance. Compare readings against Caterpillar specifications (typically 0.5-2.0 ohms for most models). Readings significantly outside this range indicate injector replacement is necessary.

Step 4: Check Circuit Voltage and Continuity With ignition on but engine off, measure voltage at the injector connector using Cat ET to command the injector. Verify battery voltage is present during activation. Check for continuity to ground in the harness—any resistance below 10k ohms suggests damaged insulation or wire chafing creating a short circuit.

Step 5: Inspect ECM Connections Remove and examine the ECM connector—a frequently overlooked step. Corrosion on pins or moisture in the connector cavity can cause erratic voltage readings. Clean with electrical contact cleaner and apply dielectric grease before reassembly.

For used excavators specifically, replace any harness sections showing wear rather than attempting tape repairs, as vibration will cause recurring failures.

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Disclaimer: This guide provides general troubleshooting information. Always consult Caterpillar service manuals specific to your machine's serial number and engine model. Complex electrical diagnostics should be performed by certified technicians with proper calibration equipment.