What is Hitachi EX200-3 Fault Code 105-3?

Fault Code 105-3 on the Hitachi EX200-3 excavator indicates an Intake Air Temperature (IAT) Sensor Circuit High Voltage condition. This diagnostic trouble code means the Engine Control Module (ECM) has detected an abnormally high voltage signal from the intake air temperature sensor circuit, typically exceeding 4.5-4.8 volts.

The IAT sensor monitors the temperature of air entering the engine's intake manifold, providing critical data the ECM uses to calculate proper fuel injection timing and quantity. On the Hitachi EX200-3's 6BD1 engine, this sensor plays a vital role in optimizing combustion efficiency and reducing emissions. When the circuit voltage reads too high, the ECM cannot accurately determine intake air density, leading to improper fuel-air mixture calculations that compromise engine performance and fuel economy.

Common Symptoms

When Code 105-3 is active, operators typically experience:

• Check Engine light illuminated on the instrument panel
• Hard starting conditions, especially during cold weather when accurate air temperature readings are most critical
• Rough idle or engine surging due to incorrect fuel delivery calculations
• Black smoke from exhaust indicating rich fuel mixture from faulty sensor data
• Reduced engine power as the ECM enters a default mode using preset temperature values instead of real-time data

Potential Causes

The most common technical reasons for Code 105-3 on used EX200-3 excavators include:

• Open circuit in sensor wiring harness – particularly where the harness routes near the engine block or valve cover, known wear points on aging machines
• Damaged or corroded connector pins at the IAT sensor plug, especially on machines with high operating hours in dusty or humid environments
• Failed IAT sensor with internal circuit breakdown causing infinite resistance
• Chafed wiring insulation where the sensor harness contacts metal brackets or engine components
• ECM internal fault (less common) affecting the 5-volt reference circuit

How to Troubleshoot and Fix Code 105-3

Step 1: Visual Inspection Begin with a thorough examination of the IAT sensor and its wiring harness. The sensor is typically located in the intake manifold or air intake tube. Check for obvious damage, corroded connectors, or wire insulation wear. On used excavators, pay special attention to harness routing near heat sources or moving components where friction damage commonly occurs.

Step 2: Electrical Testing Disconnect the IAT sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. A functioning IAT sensor should read approximately 2,000-3,000 ohms at 68°F (20°C). An infinite (open) reading confirms sensor failure. Next, check the harness side: measure voltage on the 5-volt reference wire from the ECM (key on, engine off) – it should read 4.5-5.2 volts. Measure continuity to ground on the signal return wire.

Step 3: Circuit Verification Inspect the entire harness length from sensor to ECM for chafing, cuts, or corrosion. On the EX200-3, check where the harness passes through firewall grommets and near engine mounts. Use a multimeter to verify less than 5 ohms resistance between sensor connector and ECM pins. Check for intermittent opens by wiggling the harness while monitoring resistance.

Step 4: Component Replacement If testing confirms sensor failure, replace with an OEM-equivalent IAT sensor (Hitachi part number or quality aftermarket). If wiring damage is found, repair using proper gauge wire, heat shrink connectors, and protective loom. After repairs, clear codes using diagnostic software (Hitachi Dr.EX or compatible scan tool) and perform a road test to verify the fix.

Disclaimer: This guide provides general troubleshooting information. Always consult the Hitachi EX200-3 service manual for complete specifications and safety procedures. For complex electrical issues or if you're uncomfortable working with engine management systems, seek assistance from a qualified Hitachi technician or certified heavy equipment mechanic.