What is Caterpillar Fault Code CID 356?

Caterpillar fault code CID 356 indicates "Injector Cylinder 6 - Current Below Normal or Shorted to Low Source." This diagnostic trouble code (DTC) specifically signals that the Electronic Control Module (ECM) has detected abnormally low current or a short circuit in the electrical circuit controlling the fuel injector for cylinder 6.

This code is critical for Caterpillar diesel engines because precise injector current control is essential for maintaining proper fuel delivery, combustion efficiency, and emissions compliance. When the ECM cannot maintain proper current to the injector solenoid, cylinder 6 may misfire, lose power, or cease firing altogether, leading to significant performance degradation and potential engine damage from unbalanced loading.

Common Symptoms

• Check Engine Light or malfunction indicator lamp (MIL) illuminated on the dashboard
• Rough idling or noticeable engine vibration due to cylinder 6 misfiring
• Loss of power and reduced machine performance, especially under load
• Increased fuel consumption and visible black or white exhaust smoke
• Engine derate mode may activate in severe cases, limiting machine RPM and hydraulic function

Potential Causes

The most common technical causes for CID 356 on used Caterpillar excavators include:

• Damaged injector wiring harness - particularly at rub points near the valve cover or cylinder head where vibration causes insulation wear
• Corroded or loose electrical connectors at the injector or ECM, common in machines with high hours or exposure to moisture
• Failed fuel injector solenoid in cylinder 6 due to internal coil breakdown or mechanical seizure
• ECM internal driver circuit failure affecting only the cylinder 6 output channel
• Harness chafing against engine components, creating intermittent short circuits to ground

How to Troubleshoot and Fix Code CID 356

Step 1: Visual Inspection Begin by thoroughly inspecting the injector wiring harness from cylinder 6 to the ECM. On used excavators, check for wire insulation damage, particularly where the harness contacts metal surfaces or passes through grommets. Examine all electrical connectors for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, disconnect the injector connector at cylinder 6 and measure resistance across the injector solenoid terminals (typically 0.3-0.7 ohms for most Cat injectors). Then check for continuity between each injector wire and engine ground to identify short circuits. Verify supply voltage at the injector connector with the key on (should read battery voltage).

Step 3: Component Testing and Repair If wiring tests pass, swap the cylinder 6 injector with another cylinder's injector to determine if the fault follows the component. Use Caterpillar Electronic Technician (Cat ET) diagnostic software to perform injector solenoid tests and monitor real-time current draw. Replace damaged wiring harnesses, clean corroded connectors with electrical contact cleaner, or replace the faulty injector as needed.

Critical for Used Equipment: Before replacing expensive components, thoroughly inspect harness routing and secure any loose wiring that may have shifted over years of operation, as this often resolves intermittent codes.

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Disclaimer: This guide provides general diagnostic information. Always consult your Caterpillar service manual and consider professional diesel technician assistance for complex electrical diagnostics and repairs.