Caterpillar 735 Articulated Truck Fault Code 168-4: Complete Diagnostic Guide

What is Caterpillar 735 Fault Code 168-4?

Fault Code 168-4 indicates an "Injector Cylinder 4 - Current Below Normal or Shorted to Ground" condition on the Caterpillar 735 articulated hauler equipped with the C18 ACERT engine. This diagnostic trouble code (DTC) means the Electronic Control Module (ECM) has detected abnormally low electrical current flowing through the fuel injector circuit for cylinder 4, or the circuit has a short to ground.

This fault is critical because it directly affects fuel delivery to cylinder 4. When the injector solenoid cannot receive proper current, combustion becomes incomplete or stops entirely in that cylinder, reducing engine power, increasing fuel consumption, and potentially causing damage to the diesel particulate filter (DPF) through unburned fuel contamination.

Common Symptoms

When Code 168-4 is active on your Cat 735, you may experience:

• Check Engine Light (CEL) or malfunction indicator lamp (MIL) illuminated on the dash
• Noticeable loss of power or reduced performance, especially under load
• Rough idle or engine misfiring, particularly noticeable when the machine is cold
• Increased white or black smoke from the exhaust during operation
• Engine derate mode activation in severe cases, limiting maximum speed or power output

Potential Causes

The most common technical reasons for Code 168-4 on used Cat 735 machines include:

• Faulty fuel injector solenoid on cylinder 4 (internal coil failure or mechanical sticking)
• Damaged or chafed wiring harness between the ECM and injector, particularly at harness routing points near the engine block
• Corroded or loose electrical connectors at the injector or ECM (common in machines with high hours or exposure to moisture)
• Short to ground in the injector circuit wiring due to insulation breakdown
• Failed ECM driver circuit for cylinder 4 (less common but possible in high-hour machines)
• Poor electrical ground connections at the engine block or chassis

How to Troubleshoot and Fix Code 168-4

Step 1: Visual Inspection Begin with a thorough visual inspection of the injector wiring harness for cylinder 4. On used excavators and haulers, check for wire chafing at known rub points near the valve cover, fuel lines, and engine mounting brackets. Inspect the injector connector for corrosion, moisture intrusion, or bent pins. Clean connections with electrical contact cleaner and ensure proper seating.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the injector connector and measure the resistance of the injector solenoid. Typical resistance should be between 0.3-0.7 ohms (consult your service manual for exact specifications). Next, check for continuity to ground on the injector circuit wiring with the harness disconnected from both the injector and ECM—any continuity indicates a short to ground.

Step 3: Advanced Diagnostics Connect Caterpillar Electronic Technician (Cat ET) diagnostic software to monitor injector solenoid current in real-time. The ECM should command approximately 20 amps to the injector during operation. If current remains below 5 amps with a known-good injector installed, suspect ECM internal driver failure or severe harness resistance issues.

Step 4: Component Replacement If testing confirms injector failure, replace the cylinder 4 fuel injector with a genuine Caterpillar or quality remanufactured unit. For harness damage, repair using OEM-spec wire and heat-shrink connectors rated for diesel engine environments. Always apply dielectric grease to connectors during reassembly to prevent future corrosion on used equipment.

Disclaimer: This guide provides general diagnostic information. Always consult the official Caterpillar service manual for your specific machine serial number and software calibration. Complex electrical or fuel system repairs should be performed by qualified technicians with proper diagnostic equipment.