What is Hyundai Excavator Fault Code 167-5?

Fault Code 167-5 indicates a Low Voltage condition in the Engine Coolant Temperature (ECT) Sensor Circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally low voltage signal from the coolant temperature sensor, typically below 0.2 volts. The ECM uses this sensor to monitor engine temperature and adjust fuel injection, idle speed, and fan operation accordingly.

This code is critical for Hyundai excavators because incorrect coolant temperature readings can cause the ECM to miscalculate fuel delivery, leading to poor engine performance, increased emissions, and potential overheating. The system may default to a predetermined temperature value, but this prevents optimal engine operation and can accelerate wear on critical components in used machines already experiencing age-related degradation.

Common Symptoms

• Check Engine light or warning lamp illuminated on the instrument cluster
• Engine runs rich (black smoke from exhaust) due to ECM assuming cold engine conditions
• Rough idle or difficulty starting, especially when the engine is warm
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Reduced engine power or derate mode activation in some Hyundai models

Potential Causes

The most common technical causes for Code 167-5 in used Hyundai excavators include:

• Faulty ECT sensor with internal short circuit or degraded thermistor element
• Damaged wiring harness between the sensor and ECM, particularly at rub points near the engine block or frame rails
• Corroded or loose connector pins at the sensor or ECM connection points (common in machines exposed to moisture)
• Shorted sensor ground wire creating a direct path to chassis ground
• Failed or moisture-damaged ECM (less common but possible in high-hour used equipment)

How to Troubleshoot and Fix Code 167-5

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block (typically near the thermostat housing). Check for physical damage, coolant leaks, or corrosion on the connector pins. For used excavators, carefully examine the entire wiring harness for chafing, particularly where it contacts metal surfaces or moves with engine vibration.

Step 2: Electrical Testing Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. Compare readings against Hyundai specifications (typically 2,000-3,000 ohms at 68°F/20°C). Next, check for voltage at the harness connector with the key on, engine off—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Circuit Verification Test for continuity between the sensor connector and ECM pins, and verify there's no unintended ground short (infinite resistance to ground on signal wire). Check connector terminals for corrosion or bent pins, which are extremely common failure points in aging equipment.

Step 4: Component Replacement If the sensor tests outside specifications or wiring shows damage, replace the faulty component using OEM or quality aftermarket parts. Always apply dielectric grease to connectors during reassembly to prevent future corrosion. Clear the code using Hyundai diagnostic software or a compatible scan tool and verify repair with a test cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult your Hyundai service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with excavator systems.