What is Hyundai R335LC-9T Fault Code 157-4?

Fault Code 157-4 on the Hyundai R335LC-9T excavator indicates an "Injector Cylinder 4 - Current Below Normal or Short Circuit to Ground." This Diagnostic Trouble Code (DTC) is triggered when the Electronic Control Module (ECM) detects that the electrical current flowing to the fuel injector on cylinder 4 is lower than the manufacturer's specified range, or there is a direct short circuit to ground in the injector circuit.

This code is critical because it directly affects fuel delivery to one cylinder, compromising engine performance, power output, and fuel efficiency. The Hyundai R335LC-9T is powered by a sophisticated common rail fuel injection system that requires precise electrical signals to each fuel injector solenoid. When cylinder 4's injector fails to receive proper current, the engine cannot maintain optimal combustion balance, leading to performance degradation and potential long-term engine damage.

Common Symptoms

When fault code 157-4 is active, operators typically experience:

• Rough engine idle or noticeable vibration, especially at lower RPMs
• Loss of power during digging or lifting operations, with reduced hydraulic response
• Increased fuel consumption and black or white smoke from the exhaust
• Check Engine Light illuminated on the instrument panel, possibly with a derate mode activated
• Misfiring or stumbling during acceleration or under heavy load conditions

Potential Causes

Several technical issues can trigger this fault code on used excavators:

• Failed or shorted fuel injector solenoid on cylinder 4 due to internal coil breakdown or contamination
• Damaged injector wiring harness, particularly at flex points near the valve cover where vibration causes wire insulation breakdown
• Corroded or loose electrical connectors at the injector or ECM, common in machines with high operating hours in wet or dusty environments
• ECM internal driver circuit failure affecting the cylinder 4 injector output channel
• Chafed wiring rubbing against engine components, creating intermittent ground shorts (a known issue on older R-series machines)
• Water intrusion into the injector connector causing resistance changes

How to Troubleshoot and Fix Code 157-4

Step 1: Visual Inspection Begin by thoroughly inspecting the injector wiring harness from cylinder 4 to the ECM. Look for obvious damage, chafing, or corrosion—particularly at connector pins. On used excavators, check for oil contamination in connectors and harness routing near hot exhaust components or sharp edges where insulation may have worn through.

Step 2: Electrical Testing Using a digital multimeter, disconnect the cylinder 4 injector connector and measure the injector solenoid resistance. Specification is typically 0.3-0.9 ohms (consult your service manual). Next, check the wiring harness continuity from the ECM connector to the injector plug. Measure resistance to ground on both injector wires—there should be infinite resistance (open circuit). Any reading below 10k ohms indicates a short to ground.

Step 3: Injector and ECM Testing If wiring tests pass, swap the cylinder 4 injector with another cylinder's injector. Clear codes and operate the machine. If the fault code moves to the new cylinder location, replace the fuel injector. If code 157-4 remains on cylinder 4, suspect ECM driver circuit failure or harness issues within the engine valley. Consider using Hyundai Hi-MATE diagnostic software for advanced injector balance tests and real-time current monitoring.

Step 4: Repair and Verification Repair or replace damaged components. For used machines, always apply dielectric grease to injector connectors and secure harnesses away from abrasion points with new zip ties or protective loom. After repairs, clear fault codes, run the engine through multiple load cycles, and verify the code does not return.

---

Disclaimer: This guide provides general diagnostic information. Always consult the Hyundai R335LC-9T service manual and consider professional diesel technician assistance for complex electrical or fuel system repairs. Improper diagnosis can lead to expensive component damage.