What is Caterpillar CAT 320 Fault Code $1107?

Fault Code $1107 on a Caterpillar 320 excavator indicates an Abnormal Frequency detected in the Engine Speed/Timing Sensor circuit. This diagnostic trouble code (DTC) means the Electronic Control Module (ECM) is receiving irregular or erratic signals from the primary speed/timing sensor, which monitors crankshaft position and engine RPM.

This code is critical because the CAT 320's ECM relies on precise engine speed data to control fuel injection timing, manage engine performance, and coordinate hydraulic system response. When the sensor signal becomes unstable or falls outside the manufacturer's specified frequency range (typically caused by sensor degradation or electrical interference), the machine may experience reduced power output, irregular engine operation, or enter a protective derate mode to prevent potential engine damage.

Common Symptoms

When fault code $1107 is active on your CAT 320, operators typically experience:

• Intermittent or constant check engine light illuminated on the dash display
• Rough idling or unstable engine RPM, especially during cold starts or at low idle
• Loss of power or hesitation during acceleration or under load conditions
• Engine stalling unexpectedly, particularly when transitioning from idle to working RPM
• Hydraulic system responsiveness issues due to inconsistent engine speed feedback to the ECM

Potential Causes

The most common technical reasons for code $1107 appearing on used CAT 320 excavators include:

• Worn or failing primary speed/timing sensor (magnetic pickup sensor degradation is common after 5,000+ operating hours)
• Damaged or corroded sensor wiring harness, especially at known rub points near the engine bell housing and starter motor mounting area
• Loose or corroded electrical connections at the sensor connector or ECM harness pins
• Excessive air gap between the speed sensor and the engine flywheel ring gear (typically caused by sensor mounting bracket wear or improper installation)
• Damaged flywheel ring gear teeth creating inconsistent magnetic signal patterns
• ECM software glitches or internal ECM faults (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code $1107

Step 1: Visual Inspection and Connection Check Begin by locating the primary speed/timing sensor on the engine bell housing (typically positioned near the flywheel). Inspect the sensor wiring harness for visible damage, chafing, or oil contamination—particularly where the harness routes past the starter motor. On used excavators, check for harness wear at attachment points and verify all connector pins are clean, tight, and free from corrosion. Clean connections with electrical contact cleaner and apply dielectric grease.

Step 2: Sensor Air Gap and Physical Condition Check the air gap between the sensor tip and flywheel ring gear using a feeler gauge (specification is typically 0.020-0.040 inches for CAT engines—verify in your service manual). Inspect the flywheel ring gear through the sensor opening for missing, damaged, or excessively worn teeth. Remove the sensor and examine the magnetic tip for metal debris buildup or physical damage.

Step 3: Electrical Testing Using a digital multimeter (DMM), measure the sensor's resistance (typically 200-1,000 ohms for CAT magnetic speed sensors—consult your specific model's specifications). Test the wiring harness for continuity from sensor to ECM and check for shorts to ground. Use Caterpillar Electronic Technician (CAT ET) diagnostic software to monitor real-time sensor frequency while cranking the engine—erratic readings confirm sensor or wiring issues.

Step 4: Component Replacement If testing reveals a faulty sensor, replace it with a genuine Caterpillar or OEM-equivalent part and set the proper air gap. For used machines with high operating hours, consider replacing the entire sensor-to-ECM harness section if insulation shows age-related deterioration, as intermittent faults often return due to hidden wiring damage.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult your Caterpillar service manual for model-specific procedures and specifications. For complex electrical diagnostics or if you're uncomfortable performing these tests, contact a certified CAT technician or authorized service center.