What is Hitachi Excavator Fault Code 11990-3?

Fault Code 11990-3 indicates a communication error or malfunction in the machine's Controller Area Network (CAN) bus system, specifically related to data transmission failure between the main ECM (Engine Control Module) and auxiliary control units. This diagnostic trouble code (DTC) is triggered when the primary controller detects inconsistent, missing, or corrupted data packets from connected modules within the excavator's electronic network.

In Hitachi excavators, the CAN bus system serves as the backbone for communication between the engine controller, hydraulic controller, monitor display, and various sensors. When Code 11990-3 appears, it means the ECM cannot properly communicate with one or more networked components, compromising the machine's ability to coordinate engine performance, hydraulic functions, and operator interface systems. This is critical because modern Hitachi excavators rely on seamless electronic communication to optimize fuel efficiency, manage hydraulic flow, and protect components from damage through real-time monitoring.

Common Symptoms

• Warning lights or error messages displayed on the instrument cluster, often accompanied by a master caution indicator
• Intermittent loss of monitor display functions, including fuel gauge, hour meter, or hydraulic temperature readings going blank
• Reduced engine power or derate mode activation as the ECM enters a fail-safe operating condition
• Erratic hydraulic response or delayed control inputs due to communication lag between controllers
• Engine may run rough or fail to start if critical sensor data cannot reach the ECM through the compromised network

Potential Causes

The most common technical failures triggering Code 11990-3 in used Hitachi excavators include:

• Corroded or loose CAN bus connector pins at junction points, particularly at the main harness connection behind the cab or near the engine bay where moisture intrusion is common
• Damaged CAN bus wiring harness caused by rubbing against frame components, especially at pivot points near the boom or along the undercarriage where cable routing experiences flex and vibration
• Failed termination resistor at either end of the CAN network (typically 120-ohm resistors that prevent signal reflection)
• Faulty ECM or auxiliary controller module with internal circuit board damage from age, heat cycling, or voltage spikes
• Weak battery voltage or poor grounding creating insufficient power for stable network communication
• Aftermarket component interference from improperly installed accessories that weren't integrated correctly into the CAN system

How to Troubleshoot and Fix Code 11990-3

Step 1: Visual Inspection of Wiring and Connectors Begin with a thorough physical examination of the CAN bus harness, which typically consists of twisted-pair wiring (often orange/orange-white or yellow/green depending on Hitachi model year). Inspect all connectors along the harness route from the ECM to the monitor display and auxiliary controllers. Look specifically for corrosion on pins (greenish deposits), bent terminals, or moisture inside connector housings. On used excavators, pay special attention to harness sections that pass through the cab floor and near hydraulic lines where heat and vibration cause accelerated wear.

Step 2: Measure CAN Bus Voltage and Resistance Using a digital multimeter, check the CAN bus termination resistance. With the key off and both ECM and display connectors disconnected, measure resistance between the CAN-High and CAN-Low wires—you should read approximately 60 ohms (two 120-ohm resistors in parallel). If you read infinite resistance, a termination resistor has failed or there's an open circuit. With the key on and connectors attached, measure voltage between CAN-High and ground (should be around 2.5-3.5V) and CAN-Low and ground (should be around 1.5-2.5V). Significant deviation indicates a short circuit or controller failure.

Step 3: Test with Diagnostic Software Connect Hitachi Dr.EX diagnostic software or compatible scan tool to the machine's diagnostic port. Monitor real-time CAN bus traffic and identify which specific module is failing to communicate. The software will show network status and may pinpoint whether the engine controller, hydraulic controller, or monitor is dropping offline. This step is crucial for used excavators because it prevents unnecessary parts replacement by identifying the exact failed component.

Step 4: Check Battery and Ground Connections Verify battery voltage under load (should maintain above 12.5V for 24V systems proportionally). Clean and tighten all ground straps, particularly the ECM ground and chassis grounds near electronic modules. Poor grounding is an overlooked cause in older machines where corrosion builds up over years of operation.

Step 5: Replace Failed Components Based on diagnostic findings, replace the identified faulty component—whether it's a corroded connector (consider using dielectric grease on replacements), damaged harness section (ensure proper routing away from heat and abrasion points), failed termination resistor, or malfunctioning controller module. For used excavators, always inspect replacement harness routing against OEM specifications, as previous repairs may have created new rub points.

---

Disclaimer: This guide provides general diagnostic information for Hitachi excavator fault codes. Always consult the official Hitachi service manual for your specific model and serial number. Complex electrical diagnostics should be performed by qualified technicians with proper diagnostic equipment. Improper repairs to CAN bus systems can cause additional controller damage or create safety hazards.