What is Hyundai R335LC-9T Fault Code 108-3?

Fault Code 108-3 on the Hyundai R335LC-9T excavator indicates a critical malfunction in the atmospheric pressure sensor circuit, specifically a voltage signal that is too high or outside the acceptable range. This code is generated when the Engine Control Module (ECM) detects an abnormal voltage reading from the barometric pressure sensor, which the engine management system relies upon to calculate proper air/fuel ratios and optimize combustion efficiency.

The atmospheric pressure sensor plays a vital role in the R335LC-9T's common rail diesel injection system. It measures ambient air pressure to help the ECM compensate for altitude changes and environmental conditions. When this sensor circuit reports voltage levels above manufacturer specifications (typically above 4.5-5.0 volts), the ECM cannot accurately adjust fuel delivery, potentially causing performance degradation, increased emissions, and reduced fuel economy. For used excavators operating in varying elevations or harsh job site conditions, this sensor and its wiring harness are particularly vulnerable to damage.

Common Symptoms

• Check Engine Light or MIL (Malfunction Indicator Lamp) illuminated on the instrument cluster
• Noticeable loss of engine power or difficulty reaching maximum RPM, especially at higher altitudes
• Rough idling or inconsistent throttle response during operation
• Increased black or gray exhaust smoke indicating improper fuel combustion
• Possible engine derate mode activation, limiting machine performance to protect internal components

Potential Causes

The most common causes of Code 108-3 on used Hyundai R335LC-9T excavators include:

• Damaged or corroded wiring harness connections at the atmospheric pressure sensor, particularly where the harness routes near the engine block or frame rails (known rub points on this model)
• Failed atmospheric pressure sensor due to internal component degradation, moisture intrusion, or physical damage
• Corroded or loose connector pins at the sensor plug, common in machines exposed to dust, water, or extreme temperatures
• Short circuit to power in the sensor signal wire, often caused by insulation breakdown in older machines
• ECM internal fault (rare) affecting the sensor input circuit

How to Troubleshoot and Fix Code 108-3

Step 1: Visual Inspection Begin with a thorough inspection of the atmospheric pressure sensor (typically located on or near the intake manifold or ECM housing). Examine the wiring harness for visible damage, chafing, or corrosion. On used excavators, pay special attention to connector integrity—remove the sensor connector and inspect pins for green corrosion, bent contacts, or moisture. Clean connectors with electrical contact cleaner and dielectric grease.

Step 2: Electrical Testing Using a digital multimeter (DVOM), perform voltage and resistance checks. With the ignition on and sensor disconnected, check for reference voltage from the ECM (should be approximately 5 volts). Test the signal wire for shorts to power by measuring voltage with the sensor unplugged—any reading above 0.2 volts indicates a wiring fault. Check ground circuit continuity between the sensor ground pin and chassis ground (should be less than 1 ohm).

Step 3: Sensor Testing and Replacement If wiring checks pass, test the sensor itself. Most atmospheric pressure sensors should show resistance values between 2,000-4,000 ohms depending on ambient conditions (consult Hyundai service manual for exact specifications). Compare readings at different altitudes if possible. If the sensor fails testing or shows erratic readings, replace it with an OEM or equivalent quality part. After replacement, clear codes using Hyundai Hi-Mate diagnostic software or compatible scan tool and perform a test cycle.

Step 4: Verify Repair After repairs, operate the machine through various load conditions and monitor for code recurrence. For used equipment, consider applying protective loom or heat shielding to vulnerable harness sections to prevent future failures.

---

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 cause additional damage.