What is Hitachi ZX870-5A (HCMC) Fault Code 13303-2?

Fault Code 13303-2 on the Hitachi ZX870-5A (HCMC) indicates a malfunction in the Engine Control Module (ECM) communication circuit, specifically a CAN bus communication error between the engine ECM and the machine controller. This diagnostic trouble code (DTC) signals that the Controller Area Network (CAN) data link has experienced an intermittent or complete loss of signal transmission, preventing critical operational data from being shared between control systems.

This code is particularly critical for the ZX870-5A because the HCMC (Hitachi Machine Control) system relies on constant communication between the engine management system and the hydraulic control unit to optimize performance, fuel efficiency, and emissions control. When this communication fails, the excavator's integrated systems cannot coordinate properly, leading to reduced machine capability and potential safety concerns.

Common Symptoms

• Warning lights: The malfunction indicator lamp (MIL) or engine warning light illuminates on the instrument cluster, often accompanied by a "CHECK" message on the monitor panel
• Engine derate: The machine may enter a reduced power mode or limp mode, limiting engine RPM to approximately 1,200-1,500 RPM to protect systems
• Erratic hydraulic response: Inconsistent or sluggish hydraulic functions due to improper engine-load sensing communication
• Intermittent gauge failures: Fuel level, coolant temperature, or other instrument panel readings may fluctuate or display incorrectly
• Multiple simultaneous codes: Additional CAN-related fault codes (13303-series) may appear in the diagnostic system simultaneously

Potential Causes

• Corroded or damaged CAN bus connectors: On used ZX870-5A machines, the 24-pin ECM connector and machine controller harness connectors are prone to corrosion from moisture infiltration, especially in high-humidity environments
• Wiring harness damage: The CAN-H and CAN-L twisted pair wiring running along the main chassis frame often experiences abrasion at known rub points near the engine mounting brackets and along the swing bearing cable routing
• Failed termination resistors: The 120-ohm termination resistors at each end of the CAN bus network can degrade over time, causing signal reflection and communication errors
• ECM or machine controller failure: Internal circuit board failures within the engine ECM or HCMC controller due to voltage spikes, vibration damage, or component aging
• Poor ground connections: Oxidized or loose chassis ground points (particularly G101 and G102 ground studs) can create voltage reference issues affecting CAN communication
• Aftermarket accessory interference: Improperly installed work lights, radios, or GPS systems may introduce electrical noise onto the CAN network

How to Troubleshoot and Fix Code 13303-2

Step 1: Visual Inspection and Connection Verification Begin by conducting a thorough visual inspection of all CAN bus wiring harnesses from the engine ECM (located on the right side of the engine) to the main machine controller (under the cab floor). Use a digital multimeter to check for proper continuity. Specifically inspect the harness routing near the engine firewall and along the right-side track frame where abrasion commonly occurs on used machines. Check all connector pins for corrosion, bent pins, or moisture—the 24-pin Deutsch connectors are particularly vulnerable. Clean connectors with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: Measure CAN Bus Resistance and Voltage With the ignition OFF and all connectors attached, measure the resistance between CAN-H and CAN-L terminals at the ECM connector. You should read approximately 60 ohms (two 120-ohm resistors in parallel). If you read 120 ohms, one termination resistor has failed; if you read open circuit (OL), both resistors or the wiring is compromised. With ignition ON and engine OFF, measure voltage between CAN-H and ground, then CAN-L and ground—both should read approximately 2.5 volts at rest. During cranking or communication, these voltages should oscillate between 2.0-3.0V. Use Hitachi Dr.EX diagnostic software to monitor real-time CAN bus activity and message transmission rates.

Step 3: Test Ground Circuits and Replace Components Verify all ECM ground circuits have less than 0.5 ohms resistance to battery negative. On used excavators, remove ground studs, wire-brush contact surfaces, and reinstall with star washers to ensure solid connections. If all wiring and grounds test satisfactory, the issue likely resides in the ECM or machine controller. Before replacing these expensive components ($1,500-$3,500 each), consider having the suspect module bench-tested by a qualified electronics repair facility. When sourcing replacement parts for used machines, ensure the software version matches your machine's configuration to avoid compatibility issues.

---

Disclaimer: This guide provides general troubleshooting information for informational purposes. Always consult the official Hitachi service manual for your specific machine serial number, and consider engaging a certified Hitachi technician for complex electrical diagnostics. Improper repairs may cause further damage or safety hazards.