What is Hitachi ZX350LCK-5G Fault Code 11307-4?

Fault Code 11307-4 indicates a malfunction in the DEF (Diesel Exhaust Fluid) dosing unit circuit, specifically a short circuit to ground or open circuit condition in the dosing module control wiring. This code is triggered when the Engine Control Module (ECM) detects abnormal electrical resistance or voltage in the circuit that controls the DEF injector solenoid responsible for spraying urea solution into the exhaust stream.

This fault is critical for the ZX350LCK-5G because it directly affects the Selective Catalytic Reduction (SCR) system's ability to reduce NOx emissions. When this code becomes active, the excavator may enter derate mode after a manufacturer-specified grace period, limiting engine power to 50% or less to comply with emissions regulations. For used excavators, this code often stems from aging electrical components or environmental damage to the DEF dosing unit harness.

Common Symptoms

• Amber or red warning light illuminated on the instrument cluster, often accompanied by a DEF system malfunction message
• Engine power derate occurring after 1-4 hours of operation (varies by software calibration)
• Excessive DEF consumption or complete lack of DEF usage, visible through tank level monitoring
• Rough engine performance at idle or under load due to emissions system compensation
• Persistent audible alarm in the cab indicating emissions system failure

Potential Causes

On used ZX350LCK-5G excavators, this fault code typically originates from:

• Corroded or damaged wiring harness at the DEF dosing unit connector, especially where the harness routes near the exhaust system and experiences heat cycling
• Failed DEF injector solenoid internal to the dosing module, common after 4,000-6,000 operating hours
• Chafed wiring at known rub points near the fuel tank mounting bracket or along the chassis rail
• Water intrusion into the dosing unit connector due to failed environmental seals or pressure washing damage
• ECM internal fault (less common) where the control module itself has a failed output driver circuit
• Frozen or crystallized DEF causing mechanical binding of the injector, leading to electrical overcurrent

How to Troubleshoot and Fix Code 11307-4

Step 1: Visual Inspection and Connector Check Begin by locating the DEF dosing unit mounted on the exhaust system near the SCR catalyst. Disconnect the main electrical connector and inspect for corrosion, bent pins, or moisture. On used excavators, this connector frequently shows green corrosion due to heat and DEF vapor exposure. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnecting.

Step 2: Electrical Circuit Testing Using a digital multimeter (DMM), perform resistance checks on the dosing unit solenoid. With the connector disconnected, measure resistance between the two solenoid pins—typical specification is 3-7 ohms at room temperature. Next, check for short to ground by measuring resistance from each solenoid pin to chassis ground; readings should exceed 10,000 ohms (10kΩ). Values outside these ranges indicate a failed dosing unit requiring replacement.

Step 3: Harness Continuity and Voltage Supply Trace the dosing unit harness back to the ECM connector, checking for damaged insulation at known wear points (particularly where the harness crosses the frame rail approximately 18 inches from the dosing unit). With ignition on and engine off, verify 12V supply voltage at the connector using the wiring diagram reference. Check for PWM (Pulse Width Modulation) signal from the ECM during cranking using an oscilloscope or advanced diagnostic software like Hitachi Dr.EX.

Step 4: DEF Quality and System Flush For used machines with unknown maintenance history, contaminated or degraded DEF fluid can cause dosing unit failure. Drain the DEF tank completely and inspect for crystallization or sediment. Replace the DEF filter and refill with fresh, API-certified DEF. Consider performing a dosing unit purge procedure using diagnostic software to clear any crystallized deposits.

Step 5: Component Replacement and Verification If testing confirms a failed dosing unit, replace with a genuine Hitachi part (part number specific to ZX350LCK-5G). After installation, use diagnostic software to clear fault codes and perform the DEF system initialization procedure. Monitor the system during a 30-minute test run to confirm proper operation and verify the fault does not return.

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Disclaimer: This guide provides general troubleshooting information for experienced diesel mechanics. Always consult the official Hitachi service manual for your specific machine serial number and software version. Emissions system repairs may require certified technicians to maintain warranty compliance and regulatory adherence.