What is Hyundai R335LC-9T Fault Code 105-3?

Fault Code 105-3 indicates an abnormal voltage condition in the Intake Air Heater (Grid Heater) Circuit, specifically detecting a voltage signal that is higher or lower than the manufacturer's specified range. This diagnostic trouble code (DTC) is generated by the Engine Control Module (ECM) when it detects an open circuit, short circuit, or resistance issue in the intake air heater system that assists cold-starting in diesel engines.

For the Hyundai R335LC-9T excavator, this fault affects the engine's cold-start capability and emissions performance. The intake air heater pre-warms incoming air during cold weather conditions, ensuring proper combustion and reducing white smoke during startup. When this system malfunctions, the ECM may limit engine performance or prevent starting in extreme temperatures.

Common Symptoms

• Warning lamp illuminated on the instrument cluster, often accompanied by reduced engine power
• Difficult cold starts or extended cranking time, especially in temperatures below 40°F (4°C)
• Excessive white or gray smoke from the exhaust during initial startup
• Engine derate mode activation, limiting maximum RPM and hydraulic functions
• Diagnostic display showing "105-3" on the monitor panel with potential audible warning alerts

Potential Causes

The most common technical causes for Code 105-3 on used Hyundai R335LC-9T excavators include:

• Faulty intake air heater element (grid heater burnout or internal resistance failure)
• Damaged wiring harness between the ECM and heater relay, particularly at flex points near the engine block where vibration causes wire chafing
• Corroded or loose electrical connectors at the heater element or relay module—common in machines with 5,000+ operating hours
• Failed intake air heater relay due to contact wear or coil resistance drift
• ECM internal circuit degradation (rare but possible in high-hour machines)
• Battery voltage irregularities causing inconsistent power supply to the heater circuit

How to Troubleshoot and Fix Code 105-3

Step 1: Visual Inspection Inspect the intake air heater wiring harness from the ECM to the heater element. Look for abraded insulation, particularly where the harness contacts the engine block or frame. Check all connector pins for corrosion, moisture intrusion, or bent terminals—this is critical on used excavators exposed to harsh environments.

Step 2: Electrical Testing Using a digital multimeter, measure resistance across the intake air heater element terminals (disconnect first). Typical resistance should read 0.2-0.8 ohms; infinite resistance indicates an open element. Test the heater relay by checking coil resistance (typically 70-90 ohms) and verifying proper switching function.

Step 3: Voltage Supply Check With the ignition on (engine off), verify battery voltage (12-14V) reaches the heater relay input. Activate the heater using Hyundai Hi-MATE diagnostic software or a compatible scan tool and confirm voltage output to the heater element during the glow cycle.

Step 4: Harness Continuity Perform continuity tests on all wiring between the ECM connector (Pin reference in service manual) and the heater assembly. For used machines, pay special attention to ground connections—clean and tighten all ground terminals, as corrosion resistance increases over time.

Step 5: Component Replacement Replace faulty components in this order: connectors first (if corroded), then the heater element, followed by the relay. Always use OEM or equivalent quality parts to prevent recurrence.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Hyundai service manual for your specific machine serial number, and consider professional diagnostic assistance for complex electrical issues. Improper repairs may void warranties or create safety hazards.