What is Caterpillar Fault Code EID1668?

Caterpillar Fault Code EID1668 indicates an Engine Control Module (ECM) power supply voltage abnormality, specifically detecting a voltage condition outside the acceptable operating range for critical ECM circuits. This diagnostic trouble code (DTC) triggers when the ECM detects either an overvoltage or undervoltage condition on its main power supply line, which can compromise the controller's ability to manage engine functions properly.

This fault is critical because the ECM relies on stable voltage (typically 24V nominal in Caterpillar machines) to process sensor data, control fuel injection timing, manage emissions systems, and regulate engine protection parameters. Voltage irregularities can cause erratic engine behavior, unexpected shutdowns, or failure to start—all severely impacting jobsite productivity and potentially causing secondary damage to electronic components.

Common Symptoms

• Warning lights: The malfunction indicator lamp (MIL) or check engine light illuminates on the instrument cluster
• Engine derate: Noticeable power reduction or limited RPM as the ECM enters a protective mode
• Starting difficulties: Extended cranking time, intermittent no-start conditions, or complete failure to energize the ECM
• Electrical anomalies: Flickering displays, erratic gauge readings, or intermittent loss of electronic functions
• Engine stalling: Unexpected shutdowns during operation, especially under load or during temperature changes

Potential Causes

The most frequent causes of EID1668 on used Caterpillar excavators include:

• Battery system degradation: Weak batteries, corroded terminals, or failing alternators creating voltage fluctuations
• Wiring harness damage: Chafed, pinched, or corroded wires in the main power harness, particularly at flex points near the engine mount or chassis ground connections
• Faulty main power relay: The ECM power relay stuck open, partially closed, or experiencing internal resistance
• Ground circuit failures: Corroded or loose ground straps between engine block and chassis, a common issue in machines operating in wet or coastal environments
• ECM internal fault: Less common, but voltage regulator failure within the ECM itself, more likely in machines with 8,000+ operating hours

How to Troubleshoot and Fix Code EID1668

Step 1: Verify Battery and Charging System Use a digital multimeter to check battery voltage with the engine off (should read 24-26V) and running (should read 27-29V). Load-test both batteries individually—used excavators often have mismatched or degraded batteries that cause voltage sag during cranking. Inspect all battery cable connections and clean any corrosion with a wire brush.

Step 2: Inspect Power Supply Harness and Grounds Physically trace the main power harness from the battery disconnect switch to the ECM connector. Check for wire abrasion at common rub points: steering column pass-throughs, cab mounts, and engine firewall grommets. Measure resistance on all ground circuits—readings should be below 0.5 ohms. Remove, clean, and re-torque all ground connections.

Step 3: Test ECM Power Relay and Supply Voltage Locate the ECM power relay in the main fuse/relay panel. Swap with an identical relay to rule out internal faults. Using Caterpillar Electronic Technician (Cat ET) software or a quality multimeter, backprobe the ECM connector to verify constant battery voltage on the supply pin and switched voltage on the ignition-controlled pin during key-on.

Step 4: Check for Intermittent Connections For used excavators, wiggle-test all connections while monitoring voltage with the diagnostic software connected. Connector pin corrosion is extremely common in older machines—consider applying dielectric grease after cleaning contacts with electrical contact cleaner.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Caterpillar service manual for your specific machine model and serial number. If you lack experience with high-voltage electrical systems or diagnostic software, consult a certified Caterpillar technician to prevent equipment damage or personal injury.