What is Hyundai R225LVS Fault Code 105-4?

Fault Code 105-4 on the Hyundai R225LVS excavator indicates an Intake Air Heater (Glow Plug) Circuit Low Voltage condition. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects abnormally low voltage in the intake air heater relay circuit, typically below the manufacturer's specified threshold of approximately 10-12 volts during activation.

The intake air heater system is critical for reliable cold-start performance on this Hyundai diesel engine. When the glow plug relay circuit malfunctions, the system cannot adequately preheat incoming air during cold weather conditions, leading to difficult starts, excessive white smoke, and increased engine wear during initial cranking. For used excavators operating in colder climates, this code can significantly impact daily productivity and long-term engine durability.

Common Symptoms

• Glow plug indicator light remains illuminated or flashes on the instrument cluster
• Prolonged cranking time during cold starts, especially in temperatures below 40°F (4°C)
• Excessive white or gray smoke emission during initial startup
• Rough idle for the first 30-60 seconds after cold start
• Code 105-4 stored in ECM memory, potentially triggering the malfunction indicator lamp (MIL)

Potential Causes

The most frequent causes of Code 105-4 on used R225LVS excavators include:

• Faulty intake air heater relay (common failure point after 5,000+ operating hours)
• Damaged or corroded wiring harness between the ECM and heater relay, particularly at harness routing points near the engine block where vibration causes insulation wear
• Poor ground connection at the relay mounting bracket due to corrosion or paint buildup
• Failed individual glow plugs creating excessive current draw that triggers low voltage detection
• Degraded ECM relay driver circuit (less common but possible in high-hour machines)
• Low battery voltage or weak batteries masking as a relay circuit issue

How to Troubleshoot and Fix Code 105-4

Step 1: Initial Voltage Verification Using a digital multimeter, check battery voltage with the key off (should read 12.4-12.8V). Perform a load test to ensure batteries can maintain adequate voltage during cranking. On used excavators, weak batteries frequently cause false low-voltage codes.

Step 2: Inspect Wiring Harness and Connectors Physically examine the wiring harness from the ECM to the intake air heater relay. Pay special attention to areas where the harness contacts metal surfaces or routing brackets—these are common rub-through points on R225LVS models with 3,000+ hours. Check all connector pins for corrosion, bent terminals, or moisture intrusion.

Step 3: Test the Intake Air Heater Relay Locate the relay (typically in the main fuse/relay panel). Measure voltage at the relay coil terminals with key ON—should read battery voltage. Test relay operation by applying battery voltage directly to coil terminals while measuring continuity across output terminals. Replace relay if it fails to close circuit.

Step 4: Check Ground Circuit Integrity Verify ground connection at relay mounting point shows less than 0.5 ohms resistance to battery negative. Remove, clean with wire brush, and reinstall ground connections—critical on used machines with corrosion buildup.

Step 5: Diagnostic Software Confirmation If available, use Hyundai Hi-MATE diagnostic software or compatible J1939 scan tool to monitor real-time voltage values during glow plug activation and verify proper ECM commanding.

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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 diagnosis for complex electrical issues or if you're unfamiliar with high-current electrical systems.