What is XCMG B3.9-5.9-C8.3 CM2150 Fault Code 1073-4?

Fault Code 1073-4 indicates a "Fuel Pressure Relief Valve Circuit - Voltage Below Normal or Shorted to Low Source" condition in the XCMG excavator equipped with a Cummins CM2150 electronic control system. This diagnostic trouble code (DTC) signals that the Engine Control Module (ECM) has detected abnormally low voltage in the electrical circuit controlling the fuel pressure relief valve solenoid, typically below the manufacturer's specified threshold of approximately 0.5 volts.

This code is critical for XCMG machines using Cummins B3.9, 5.9, or C8.3 engines because the fuel pressure relief valve maintains proper common rail fuel pressure (typically 1,600-2,000 bar). When the ECM cannot properly command this valve due to circuit issues, fuel pressure regulation becomes compromised, directly affecting engine performance, fuel economy, and emissions compliance.

Common Symptoms

• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Engine power derate or reduced performance, particularly under heavy load conditions
• Hard starting or extended cranking time, especially when the engine is cold
• Rough idle or inconsistent engine RPM fluctuations during low-load operation
• Black smoke from the exhaust due to improper fuel pressure management

Potential Causes

The most common technical causes for fault code 1073-4 on used XCMG excavators include:

• Damaged wiring harness between the ECM and fuel pressure relief valve, particularly at known rub points near the engine block or fuel pump mounting bracket
• Corroded or loose electrical connectors at the relief valve solenoid—common in machines operating in wet or corrosive environments
• Failed fuel pressure relief valve solenoid with internal short circuit to ground
• Chafed or pinched wires in the engine harness, often caused by improper routing during previous repairs
• ECM internal fault affecting the driver circuit for the relief valve (less common but possible in high-hour machines)
• Poor ground connection at the ECM or engine block ground strap

How to Troubleshoot and Fix Code 1073-4

Step 1: Visual Inspection Begin with a thorough inspection of the fuel pressure relief valve wiring harness. On used excavators, focus on areas where the harness contacts the engine block, fuel lines, or frame members. Look for abraded insulation, oil contamination, or heat damage. Inspect the connector at the relief valve for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the relief valve connector and perform resistance checks. Measure resistance between the solenoid terminals—typical specification is 2-5 ohms. Then check for shorts to ground by measuring resistance between each solenoid terminal and engine ground (should read infinite/open circuit). Check supply voltage from the ECM connector (key on, engine off) which should read battery voltage (12-14V).

Step 3: Circuit Continuity and Repair With the Cummins INSITE diagnostic software connected, perform an actuator test to command the relief valve while monitoring voltage. If voltage drops below 1V during actuation, suspect wiring issues. Trace the circuit from ECM connector back to the valve, checking for continuity. For used machines, pay special attention to connector terminals—clean with electrical contact cleaner and apply dielectric grease. Replace damaged sections of harness using proper gauge wire (typically 18-20 AWG) and heat-shrink connectors.

Step 4: Component Replacement If wiring tests pass but the code persists, replace the fuel pressure relief valve assembly. Ensure the replacement part meets Cummins specifications for the CM2150 system. After replacement, clear codes with INSITE and perform a fuel pressure test to verify proper operation (typically 1,400-1,800 bar at rated RPM).

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the manufacturer's service manual and follow proper safety procedures. For complex electrical or fuel system issues on used excavators, professional diagnosis with OEM diagnostic tools is recommended to avoid misdiagnosis and unnecessary parts replacement.