What is Hyundai R505LC-7 Fault Code 1265-4?

Fault Code 1265-4 on the Hyundai R505LC-7 excavator indicates a "Throttle Position Sensor 2 (TPS2) Circuit Voltage Below Normal or Shorted Low." This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally low voltage signal from the secondary throttle position sensor, typically below 0.5 volts when it should read between 0.5-4.5 volts during normal operation.

The TPS2 is a critical redundancy sensor that works alongside TPS1 to provide the ECM with accurate accelerator pedal position data. On the R505LC-7's electronically-controlled diesel engine, this dual-sensor system ensures precise fuel delivery and engine speed control. When TPS2 fails or provides faulty signals, the machine may enter derate mode (reduced power output) to prevent engine damage, significantly impacting productivity on job sites.

Common Symptoms

• Engine derate or limp mode – machine operates at reduced power (typically 50-70% capacity)
• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the instrument cluster
• Erratic throttle response or delayed acceleration when moving the control lever
• Engine stalling or rough idle, particularly when transitioning from idle to working speed
• Inability to reach full RPM even under full throttle demand

Potential Causes

The most frequent causes of Code 1265-4 on used R505LC-7 excavators include:

• Damaged or corroded TPS2 connector – common on machines with 5,000+ hours due to exposure to moisture and vibration
• Wiring harness chafing at known rub points near the engine firewall or fuel injection pump bracket
• Failed throttle position sensor – internal potentiometer wear causes inconsistent voltage output
• Short to ground in the TPS2 signal wire (typically a gray or yellow wire in Hyundai harnesses)
• Poor ground connection at the ECM or sensor mounting point
• ECM internal fault – rare but possible on high-hour machines with previous electrical issues

How to Troubleshoot and Fix Code 1265-4

Step 1: Visual Inspection of Wiring and Connectors Start by inspecting the TPS2 connector located on the accelerator pedal assembly or throttle actuator. On used excavators, carefully check for corrosion, bent pins, or moisture intrusion. Disconnect the connector and apply electrical contact cleaner, then inspect the wiring harness for signs of abrasion or damage along its routing path.

Step 2: Voltage and Resistance Testing Using a digital multimeter (DMM), backprobe the TPS2 signal wire with the key on, engine off (KOEO). You should read approximately 0.5-1.0 volts at idle pedal position and 4.0-4.5 volts at full throttle. Check the 5-volt reference supply from the ECM (should be a steady 5.0V ± 0.1V). Test ground continuity – resistance should be less than 1 ohm to chassis ground.

Step 3: Sensor Replacement or Harness Repair If voltage readings are erratic or absent, disconnect the sensor and measure its internal resistance (typically 1-5k ohms between signal and ground terminals). Replace the TPS2 sensor if readings fall outside specifications. For wiring issues, repair any shorted or open circuits using OEM-grade wire and heat-shrink connectors. On used machines, consider replacing the entire pedal assembly harness if multiple chafe points exist.

Step 4: Clear Codes and Verify Repair After repairs, use Hyundai Hi-MATE diagnostic software or a compatible scan tool to clear fault codes. Perform a throttle relearn procedure if required by the service manual. Test-operate the machine under load to ensure the code does not return and full power is restored.

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Disclaimer: This guide provides general diagnostic information for Hyundai R505LC-7 excavators. Always consult the official service manual and consider professional diagnosis for complex electrical issues. Improper repairs may cause further damage or safety hazards.