What is Caterpillar Fault Code EID1735?

Caterpillar Fault Code EID1735 indicates an "Engine Speed/Position Sensor Circuit - Abnormal Frequency, Pulse Width, or Period." This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects irregular or erratic signals from the engine speed/position sensor, preventing accurate monitoring of crankshaft position and engine RPM.

This fault is critical because the speed/position sensor provides essential data for fuel injection timing, engine speed regulation, and overall performance. When this sensor circuit fails or sends corrupted signals, the ECM cannot properly control combustion events, potentially causing engine performance issues, misfires, or complete shutdown. In Caterpillar excavators, this sensor is fundamental to coordinating the high-pressure fuel system and ensuring smooth operation under varying loads.

Common Symptoms

• Engine fails to start or experiences prolonged cranking before starting
• Erratic engine RPM or unexpected surging and hunting at idle
• Loss of power or engine derate mode activation to protect components
• Check Engine light or diagnostic warning illuminated on the instrument cluster
• Engine stalling during operation, particularly under load or when transitioning between idle and working RPM

Potential Causes

The most common technical causes for EID1735 in used Caterpillar excavators include:

• Worn or damaged speed/position sensor due to heat exposure, vibration, or age-related deterioration
• Corroded or loose connector pins at the sensor harness connection point
• Damaged wiring harness from rubbing against engine components, particularly near the flywheel housing where routing is tight
• Metal debris contamination on the sensor face or flywheel ring gear, affecting magnetic field detection
• Faulty ECM or internal circuit board issues (less common but possible in high-hour machines)
• Incorrect air gap between sensor tip and flywheel teeth due to sensor mounting issues

How to Troubleshoot and Fix Code EID1735

Step 1: Visual Inspection Begin by inspecting the speed/position sensor location (typically mounted on the flywheel housing). Check for physical damage, oil contamination, or metal shavings on the sensor tip. On used excavators, examine the wiring harness routing for signs of chafing, heat damage, or previous repairs with electrical tape.

Step 2: Connector and Resistance Testing Disconnect the sensor connector and inspect pins for corrosion, bent contacts, or moisture intrusion. Using a digital multimeter, measure sensor resistance (typically 200-1000 ohms for Caterpillar sensors—verify specifications in your service manual). Test harness continuity from sensor connector to ECM to identify open circuits or shorts to ground.

Step 3: Signal Testing and Air Gap Verification Using Caterpillar Electronic Technician (Cat ET) diagnostic software, monitor live sensor signal frequency while cranking the engine. Erratic or absent signals confirm sensor failure. Check the air gap between sensor and flywheel teeth (typically 0.020-0.050 inches); incorrect spacing causes signal distortion. Clean metal debris from the sensor face and flywheel area.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Caterpillar speed/position sensor and apply dielectric grease to connector terminals. For used machines with high hours, consider replacing the sensor harness simultaneously if insulation shows deterioration. Clear codes with diagnostic software and perform a test run under load.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific model and serial number. If unfamiliar with electrical diagnostics or high-pressure fuel systems, seek assistance from a certified Caterpillar technician to prevent equipment damage or safety hazards.