What is Caterpillar Fault Code CID673?

Caterpillar Fault Code CID673 indicates "Injector Cylinder #6 - Current Below Normal or Shorted to Low Source." This diagnostic trouble code (DTC) signals that the Engine Control Module (ECM) has detected abnormally low electrical current flowing to the fuel injector on cylinder 6, or the circuit has shorted to ground.

This code specifically affects the electronic unit injector (EUI) system used in Caterpillar diesel engines. The ECM continuously monitors injector solenoid current during operation. When current falls below the manufacturer's specified threshold (typically 18-20 amps during injection events), CID673 triggers. This is critical because proper injector current ensures precise fuel metering, combustion efficiency, and emissions compliance. On used excavators, this fault can lead to power loss, rough operation, and potential damage to the catalytic converter if unburned fuel enters the exhaust system.

Common Symptoms

• Check Engine Light or malfunction indicator lamp (MIL) illuminated on the instrument panel
• Noticeable power loss or reduced engine performance, especially under load during digging or lifting operations
• Rough idle or engine misfiring, with cylinder #6 not contributing properly to combustion
• Excessive white or black smoke from the exhaust due to incomplete combustion
• Possible engine derate mode activation on newer models with emissions systems, limiting machine productivity

Potential Causes

The most common technical causes for CID673 on used Caterpillar excavators include:

• Faulty injector solenoid on cylinder #6 due to internal coil breakdown or mechanical wear
• Damaged wiring harness between the ECM and injector, particularly at known rub points near the valve cover or engine block
• Corroded or loose electrical connectors at the injector or ECM—extremely common on machines operating in wet or corrosive environments
• Shorted injector harness to engine ground due to insulation degradation from heat cycling and age
• Failed ECM injector driver circuit (less common but possible on high-hour machines)
• Low supply voltage from battery or charging system issues affecting injector performance

How to Troubleshoot and Fix Code CID673

Step 1: Visual Inspection Begin with a thorough inspection of the injector #6 harness and connector. On used excavators, check for abraded wires at valve cover edges, melted insulation near exhaust components, or oil contamination inside connectors. Clean all connections with electrical contact cleaner and inspect pins for corrosion or damage.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the injector connector and measure solenoid resistance across the injector terminals. Caterpillar injectors typically read 0.3-0.7 ohms. Values outside this range indicate injector failure. Next, check for short to ground by measuring resistance between each injector terminal and engine ground—readings below 10,000 ohms indicate harness damage.

Step 3: ECM and Harness Verification Connect Caterpillar Electronic Technician (Cat ET) diagnostic software to perform active injector solenoid tests. Monitor actual injector current during cranking. If current remains low despite proper resistance readings, inspect the ECM-to-injector harness for internal breaks. On used machines, carefully trace the entire harness route, as vibration and heat cycles often cause conductor fatigue. Check supply voltage at the injector connector during cranking—should read battery voltage (12V or 24V depending on system).

Step 4: Component Replacement Replace the cylinder #6 injector if resistance or operational tests fail. Always use genuine Caterpillar injectors or verified remanufactured units with proper calibration codes. If harness damage is found, repair or replace the affected section with proper heat-resistant, abrasion-resistant wire and secure away from rub points.

Disclaimer: This guide provides general troubleshooting information. Always consult the specific Caterpillar service manual for your machine model and serial number. Complex electrical diagnostics should be performed by certified technicians with proper diagnostic tools and safety equipment.