What is Caterpillar Fault Code EID668?

Caterpillar Fault Code EID668 indicates an Engine Idle Shutdown System malfunction, specifically reporting that the idle shutdown timer has been disabled or is not functioning correctly within the Electronic Control Module (ECM). This diagnostic code appears when the machine's automatic idle shutdown feature fails to operate according to programmed parameters, preventing the engine from shutting down after a specified period of idling.

The idle shutdown system is designed to reduce unnecessary fuel consumption, minimize engine wear, and decrease emissions during extended idle periods. When EID668 triggers, the ECM detects that the shutdown timer circuit has been interrupted, manually overridden, or has experienced a communication error. For Caterpillar excavators, especially used machines with accumulated operating hours, this fault can indicate underlying electrical issues or intentional operator modifications that bypass fuel-saving protocols. Proper function of this system is critical for meeting emissions standards and optimizing operational costs.

Common Symptoms

• Idle shutdown feature becomes completely inoperative, allowing the engine to run indefinitely without automatic shutdown
• Warning message displayed on the monitor panel indicating idle shutdown system disabled or fault condition
• Engine continues running beyond programmed idle time without entering shutdown sequence
• Increased fuel consumption during standby operations due to prolonged unnecessary idling
• Check Engine light or service indicator may illuminate on certain model configurations

Potential Causes

The most common technical reasons for EID668 on used Caterpillar excavators include:

• Idle shutdown switch manually disabled by operator or previous owner through cab-mounted override switch
• Damaged wiring harness between the idle shutdown switch and ECM, particularly at flex points near the cab mounting or door hinges
• Corroded or loose electrical connectors in the idle shutdown circuit due to age and environmental exposure
• ECM programming changes or parameter modifications that conflict with factory idle shutdown settings
• Faulty idle shutdown timer relay or associated control module component failure
• Voltage irregularities in the machine's electrical system affecting timer circuit operation

How to Troubleshoot and Fix Code EID668

Step 1: Verify Idle Shutdown Switch Position Begin by locating the idle shutdown override switch typically found on the operator console or dashboard. Ensure it's in the enabled position. Many used excavators have had this feature intentionally disabled by previous operators who preferred manual control.

Step 2: Inspect Wiring and Connectors Using a multimeter, check for continuity in the wiring harness between the idle shutdown switch and the ECM connector. Pay special attention to known wear points where harnesses route through the cab frame or near hydraulic lines. Look for chafed insulation, corroded pins, or loose connections at connector C3 (varies by model year). Clean all connections with electrical contact cleaner and apply dielectric grease.

Step 3: Test Voltage and Circuit Integrity With the key switch on (engine off), measure voltage at the idle shutdown switch – you should see battery voltage (approximately 12-14V). Activate the switch and verify voltage changes at the ECM input pin. Consult Caterpillar Electronic Technician (Cat ET) software to verify ECM parameters haven't been altered and that the timer setpoint matches operational requirements.

Step 4: Verify ECM Programming Connect Cat ET diagnostic software and review idle shutdown parameters. For used excavators, verify the timer hasn't been set to maximum duration (essentially disabling the feature). Reset to manufacturer specifications if needed and clear the fault code.

Step 5: Component Replacement if Necessary If all electrical checks pass, the idle shutdown relay or internal ECM timer circuit may have failed. This is more common in high-hour used machines. Replace the relay module first before considering ECM replacement, as it's significantly less expensive.

Disclaimer: This guide provides general troubleshooting information. Always consult your Caterpillar service manual for model-specific procedures and safety precautions. If you're unfamiliar with electrical diagnostics or working with ECM systems, seek assistance from a certified Caterpillar technician to avoid damage to electronic components.