What is Caterpillar 320GC Fault Code 1593-6?

Caterpillar 320GC Fault Code 1593-6 indicates an "Engine Synchronization Reference Signal - Voltage Above Normal" condition. This diagnostic trouble code (DTC) means the Electronic Control Module (ECM) is receiving an abnormally high voltage signal from the engine speed/timing sensor circuit, specifically the synchronization reference sensor that monitors crankshaft or camshaft position.

This fault directly affects the ECM's ability to properly time fuel injection and manage engine performance. The synchronization reference sensor provides critical data for calculating engine speed, piston position, and injection timing. When voltage exceeds manufacturer specifications (typically above 5.0-5.5 volts on Caterpillar systems), the ECM cannot reliably interpret engine position data, potentially causing performance issues or protective shutdowns. For the 320GC excavator's C4.4 ACERT engine, accurate synchronization is essential for maintaining fuel efficiency, emissions compliance, and smooth hydraulic system operation.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument panel
• Engine derate mode activated, limiting maximum RPM and reducing available power
• Rough idling or inconsistent engine speed, particularly noticeable during hydraulic operations
• Hard starting or extended cranking time, especially when the engine is cold
• Intermittent power loss during operation, with the machine occasionally returning to normal function

Potential Causes

The most common technical causes for Code 1593-6 on used Caterpillar 320GC excavators include:

• Damaged or frayed wiring harness near the engine timing sensor, particularly where the harness contacts the engine block or frame (a known wear point on used machines)
• Corroded or moisture-contaminated connectors at the synchronization sensor or ECM connection points
• Failed engine speed/timing sensor with internal short-circuit causing high voltage output
• ECM internal fault affecting voltage regulation in the sensor reference circuit
• Improper sensor installation or incorrect air gap between sensor and reluctor wheel (common after previous repairs on used equipment)
• Damaged reluctor wheel or missing teeth causing erratic signal generation

How to Troubleshoot and Fix Code 1593-6

Step 1: Visual Inspection Begin by thoroughly inspecting the engine speed sensor wiring harness from the sensor to the ECM connector. On used excavators, check for harness routing that may cause rubbing against the engine block, frame rails, or hydraulic lines. Look for abraded insulation, exposed copper, or melted wire covering. Inspect all connector pins for corrosion, bent terminals, or moisture intrusion—these are extremely common failure points on older machines.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the engine speed sensor and measure resistance across the sensor terminals (typically 200-1,000 ohms depending on sensor type—consult service manual). Then check for voltage at the ECM-side harness connector with ignition on, engine off. You should see approximately 5-8 volts of reference voltage. If voltage reads above 10 volts or fluctuates wildly, suspect harness short-to-power or ECM malfunction.

Step 3: Sensor Air Gap and Component Testing Remove the synchronization sensor and inspect the reluctor wheel for damage, missing teeth, or excessive debris buildup. Verify sensor air gap specification (typically 0.020-0.050 inches) using feeler gauges during reinstallation. For used excavators, consider replacing the sensor even if it tests within specification, as internal intermittent failures are common. Clear the code using Caterpillar Electronic Technician (Cat ET) diagnostic software and perform a test run.

Step 4: Advanced Diagnostics If the fault persists after sensor and harness repair, use Cat ET software to monitor live sensor data and voltage readings during engine operation. Intermittent high voltage may indicate ECM internal problems requiring ECM replacement or professional reprogramming.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific machine serial number. For complex electrical diagnostics or ECM replacement, contact a certified Caterpillar technician or authorized service center.