What is Hyundai R335LC-9T Fault Code 157-3?

Fault Code 157-3 on the Hyundai R335LC-9T excavator indicates an "Injector Cylinder #3 - Voltage Below Normal" condition. This code triggers when the Electronic Control Module (ECM) detects abnormally low voltage in the electrical circuit controlling the fuel injector for cylinder number three.

This diagnostic trouble code specifically monitors the injector driver circuit within the engine's common rail fuel injection system. The Hyundai D6CA diesel engine used in the R335LC-9T relies on precise electronic control of each injector to maintain optimal combustion efficiency, fuel economy, and emissions compliance. When voltage drops below the manufacturer's specified threshold (typically below 10-12 volts during injector activation), the ECM logs this fault and may initiate protective measures to prevent engine damage.

Common Symptoms

• Engine misfiring or rough idle, particularly noticeable at low RPMs or during warm-up
• Illuminated engine warning light on the instrument cluster, possibly accompanied by reduced engine power (derate mode)
• Loss of hydraulic performance due to decreased engine output affecting hydraulic pump efficiency
• Increased black or white smoke from the exhaust, indicating incomplete combustion in cylinder #3
• Diagnostic display showing active fault code 157-3 when using the machine's built-in monitoring system

Potential Causes

Electrical Harness Issues: In used excavators, the most common cause is damaged or corroded wiring near the #3 injector connector, especially where the engine harness rubs against the valve cover or injection pump bracket during engine vibration.

Faulty Fuel Injector: The electromagnetic solenoid within the #3 injector may have developed an internal short circuit or open winding, reducing electrical resistance and causing voltage drop.

Corroded Connectors: The weatherpack connector at cylinder #3 often accumulates moisture and corrosion on used machines, increasing circuit resistance and lowering available voltage.

ECM Driver Failure: The injector driver transistor inside the ECM itself may be failing, though this is less common than external wiring issues.

Poor Ground Connections: Degraded ground straps between the engine block and chassis can cause voltage reference problems affecting injector circuits.

How to Troubleshoot and Fix Code 157-3

Step 1: Visual Inspection Begin by thoroughly inspecting the wiring harness and connector at cylinder #3 injector. On used R335LC-9T excavators, check specifically where the harness passes over the valve cover—this is a known wear point. Look for chafed insulation, broken wires, or corroded pins in the injector connector.

Step 2: Electrical Testing Using a digital multimeter, perform resistance checks on the #3 injector. Disconnect the injector connector and measure resistance across the injector terminals; typical specification is 0.3-0.8 ohms. Compare this reading to other cylinders. Next, check for voltage supply from the ECM with the key on, engine off—you should see battery voltage momentarily during cranking.

Step 3: Connector Service and Ground Verification Clean the #3 injector connector thoroughly with electrical contact cleaner and apply dielectric grease. Inspect all connector pins for proper tension. Verify engine ground straps are tight and corrosion-free, paying special attention to the ground connection on the cylinder head near injector #3.

Step 4: Component Replacement If wiring and connectors check good but resistance is out of specification, replace the #3 fuel injector with a genuine Hyundai or quality aftermarket unit. For used excavators with high hours, consider having injectors professionally tested and flow-matched before replacement.

Step 5: Clear Codes and Verify After repairs, use Hi-MATE diagnostic software or equivalent Hyundai diagnostic tool to clear fault codes and perform an injector cutout test to confirm cylinder #3 is functioning properly.

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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 engaging a certified heavy equipment technician for complex electrical diagnostics or fuel system repairs.