What is Hyundai Excavator Fault Code ER35?

Fault Code ER35 indicates a malfunction in the engine preheating system, specifically related to the glow plug relay circuit or glow plug operation failure. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage reading, open circuit, or excessive resistance in the glow plug system during the preheating cycle.

The glow plug system is critical for cold-start performance on Hyundai excavators equipped with diesel engines. When ER35 appears, the ECM has identified that the preheating system cannot adequately warm the combustion chambers before starting. This is particularly problematic in used machines operating in cold climates, as it directly affects engine startability and can lead to increased wear during cold starts. The system relies on proper voltage delivery through the glow plug relay, wiring harness integrity, and functional glow plugs to ensure smooth engine ignition.

Common Symptoms

• Hard starting or extended cranking time, especially in cold weather conditions or after the machine has sat overnight
• Glow plug indicator light remains illuminated continuously or fails to activate during the normal preheating cycle
• White or gray exhaust smoke during initial startup due to incomplete combustion
• Rough idle or engine misfiring immediately after cold starts until the engine reaches operating temperature
• Warning message displayed on the instrument cluster indicating a preheating system fault

Potential Causes

The most common technical causes for ER35 on used Hyundai excavators include:

• Failed glow plug relay due to contact wear or coil burnout from repeated cycling over the machine's lifespan
• One or more defective glow plugs with broken heating elements or excessive carbon buildup reducing conductivity
• Damaged wiring harness between the relay and glow plugs, particularly at stress points near the engine block where vibration causes wire chafing
• Corroded electrical connectors at the glow plug relay, individual glow plugs, or ECM connections due to moisture intrusion
• Low battery voltage or weak alternator output affecting the relay's ability to energize properly
• ECM programming issues or internal ECM failure (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code ER35

Step 1: Visual Inspection and Voltage Check Begin by inspecting all visible wiring from the glow plug relay to each individual glow plug. Look for abraded insulation, especially where harnesses contact the engine block or valve cover. Check battery voltage with a multimeter—it should read 12.4-12.8V with the engine off. Inspect the glow plug relay connector for corrosion or burnt terminals.

Step 2: Test Glow Plug Relay Operation Using a multimeter, check for battery voltage at the relay input terminal with the key in the preheat position. The relay should click audibly when activated. Test continuity through the relay when energized. If no click occurs or continuity fails, replace the glow plug relay. On used excavators, relays often fail due to contact degradation from thousands of heating cycles.

Step 3: Individual Glow Plug Resistance Testing Disconnect the electrical connector from each glow plug. Measure resistance from the glow plug terminal to ground—typical specifications range from 0.5 to 2.0 ohms depending on the specific Hyundai engine model. A reading of infinite resistance indicates an open (failed) glow plug. Remove and physically inspect any suspect glow plugs for tip damage or excessive carbon deposits, which are common in used machines with inconsistent maintenance history.

Step 4: Harness Continuity and Voltage Drop Test With the relay energized, measure voltage at each glow plug connector. You should see full battery voltage (11-12V minimum). Significant voltage drop indicates high resistance in the harness. Pay special attention to harness routing near engine mounts and exhaust manifolds where heat and vibration cause insulation breakdown in older machines.

Step 5: Clear Code and Verify Repair After replacing faulty components, use Hyundai diagnostic software (Hi-MATE or compatible scan tool) to clear ER35 and monitor glow plug system operation during a cold start cycle. Verify proper preheat timing and that all glow plugs reach operating temperature.

Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official Hyundai service manual for your specific excavator model and serial number. If you're uncomfortable performing electrical diagnostics, consult a certified Hyundai technician or qualified heavy equipment mechanic to prevent further damage to the electrical system.