What is Hyundai R385LVS Fault Code 105-3?

Fault Code 105-3 on the Hyundai R385LVS excavator indicates an Intake Air Temperature (IAT) Sensor Circuit High Voltage condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the intake air temperature sensor, typically exceeding 4.8-4.9 volts for more than 0.5 seconds.

The IAT sensor measures incoming air temperature in the intake manifold, allowing the ECM to calculate proper fuel injection timing and air-fuel ratios. When this sensor reports incorrect high voltage readings, the ECM cannot accurately adjust fuel delivery for optimal combustion, directly impacting engine performance, fuel economy, and emissions compliance on this 38-ton class excavator.

Common Symptoms

When Code 105-3 is active on your R385LVS, you may experience:

• Check Engine Light (CEL) illuminated on the instrument cluster with reduced engine power
• Hard starting or extended cranking time, especially in cold weather conditions
• Black smoke from the exhaust due to improper fuel mixture calculations
• Rough idling or engine hesitation during acceleration under load
• Increased fuel consumption as the ECM defaults to preprogrammed backup values

Potential Causes

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

• Open circuit or broken wiring in the IAT sensor harness, particularly at known rub points near the engine valley and intake manifold mounting brackets
• Corroded or damaged sensor connector pins due to moisture intrusion or age-related deterioration
• Failed IAT sensor with internal circuit degradation (common after 5,000+ operating hours)
• Damaged ECM sensor supply circuit providing incorrect reference voltage
• Aftermarket intake modifications or missing air filter components causing sensor exposure to debris
• Harness chafing against turbocharger components or exhaust manifold shields

How to Troubleshoot and Fix Code 105-3

Step 1: Visual Inspection Begin by inspecting the IAT sensor and its wiring harness located in the intake manifold near the air filter housing. Check for physical damage, corroded connector pins, moisture contamination, or wire insulation wear at known friction points. On used excavators, examine the harness routing for modifications or repairs that may have compromised wire integrity.

Step 2: Electrical Testing Using a digital multimeter, disconnect the IAT sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). Next, check for supply voltage at the harness connector with ignition on—you should see approximately 5 volts on the signal wire.

Step 3: Circuit Continuity Check Test continuity between the ECM connector and the IAT sensor harness connector to identify open circuits. Measure resistance—it should be less than 5 ohms. Also check for short-to-power conditions that would cause high voltage readings.

Step 4: Component Replacement If the sensor tests out of specification or wiring shows damage, replace the IAT sensor (part typically costs $45-$85) or repair damaged harness sections. For used machines, always apply dielectric grease to connector pins to prevent future corrosion. Clear codes using Hyundai diagnostic software (Hi-MATE or compatible scan tool) and perform a test cycle.

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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 or if you're unfamiliar with high-voltage systems.