Hyundai HX220 NL EPFC Fault Code 3396 (3750-31): Meaning and Fix

What is Hyundai HX220 NL EPFC Fault Code 3396 (3750-31)?

Fault Code 3396 (3750-31) indicates a malfunction in the engine control system's communication circuit, specifically related to CAN (Controller Area Network) bus communication errors between the ECM (Engine Control Module) and other control units.

This code triggers when the ECM detects abnormal or interrupted data transmission on the CAN bus network, which is the digital communication backbone connecting the engine controller, hydraulic controller, and display panel. For the HX220 NL EPFC model, this communication failure can severely impact machine performance because the ECM cannot properly coordinate fuel injection timing, hydraulic pump output, or operator interface functions. Left unresolved, this fault can cause unpredictable machine behavior and potential safety hazards.

Common Symptoms

• Warning lamp illuminated on the instrument cluster with reduced engine power (derate mode activated)
• Erratic hydraulic response or sluggish boom/arm movements due to loss of load-sensing data
• Intermittent display failures where gauges freeze or show incorrect readings
• Engine may enter limp mode, limiting RPM to 1200-1500 to protect components
• Multiple fault codes appearing simultaneously as other modules lose communication

Potential Causes

The most common technical causes for Code 3396 in used HX220 excavators include:

• CAN bus wiring harness damage at known rub points near the engine mount brackets or along the right-side frame rail where harnesses contact metal edges
• Corroded or loose connector pins at the ECM connector (C101) or hydraulic controller connector, especially in machines operated in wet or coastal environments
• Failed termination resistor (120-ohm) at either end of the CAN bus network
• ECM internal failure affecting the CAN transceiver circuit (less common but possible in high-hour machines)
• Voltage supply issues to control modules caused by failing main relay or poor ground connections at G301 ground point

How to Troubleshoot and Fix Code 3396 (3750-31)

Step 1: Visual Inspection Begin with a thorough harness inspection. On used excavators, focus on the main engine harness routing from the ECM (located behind the operator cab) forward to the engine. Check for abraded insulation, pinched wires, or evidence of previous repairs. Pay special attention to connector C101 at the ECM—remove it and inspect pins for corrosion or bent contacts.

Step 2: Electrical Testing Using a digital multimeter, measure CAN-High and CAN-Low resistance. With ignition off and both connectors at the ECM and hydraulic controller disconnected, you should read approximately 60 ohms between CAN-H and CAN-L (indicating both 120-ohm termination resistors in parallel). If you read 120 ohms, one terminator has failed. If you read open circuit, there's a wiring break.

Step 3: Voltage and Signal Verification With ignition on (engine off), backprobe the CAN-High wire (typically yellow/green) and CAN-Low wire (typically yellow/brown) at the ECM connector. You should see approximately 2.5V DC on each line when idle. During cranking or with diagnostic software active, observe for voltage fluctuations between 2.0-3.5V—this indicates data transmission. No voltage change suggests a failed ECM CAN transceiver.

Step 4: Harness Continuity Check For used machines with high hours, perform a wiggle test while monitoring live data with Hyundai Hi-MATE diagnostic software or equivalent. Flex the harness at suspected wear points while watching for communication dropouts. This often reveals intermittent opens that standard testing misses.

Step 5: Component Replacement If testing confirms harness damage, repair using OEM-spec twisted-pair shielded cable (not standard wire). If the ECM connector shows corrosion, replace the entire pigtail connector rather than individual pins. For failed termination resistors, these are typically integrated into the controller connectors and require connector replacement.

Disclaimer: This guide provides general diagnostic procedures. Complex electrical issues may require factory diagnostic software and trained technicians. Always consult the official Hyundai service manual and consider professional assistance for critical repairs on used heavy equipment.