What is Caterpillar Fault Code SPN1667?

SPN 1667 indicates an abnormal frequency, pulse width, or period detected in the Engine Starter Motor circuit. This Suspect Parameter Number (SPN) specifically monitors the electrical signals and performance characteristics of the starter motor system during cranking events.

In Caterpillar electronic control systems, the Engine Control Module (ECM) continuously monitors starter motor operation to detect irregular electrical patterns that could indicate circuit problems, mechanical binding, or component degradation. This code is critical because starter system malfunctions can leave your excavator completely inoperable, and irregular electrical signals may indicate underlying issues that could damage the starter solenoid, relay circuits, or even the ECM itself. On used excavators, this fault often emerges as wiring insulation deteriorates or connections corrode over time.

Common Symptoms

• Intermittent or failed starting attempts with the starter motor cranking erratically or not engaging properly
• Extended cranking times before the engine fires, or the starter disengaging prematurely during cranking
• Clicking or chattering sounds from the starter solenoid area indicating irregular power delivery
• Warning lamp illumination on the instrument cluster with stored diagnostic codes
• Complete no-crank condition in severe cases where the ECM has disabled starter operation for protection

Potential Causes

The most common technical causes for SPN 1667 on used Caterpillar excavators include:

• Corroded or loose battery cable connections at the starter motor, solenoid, or ground points causing voltage drops and irregular signals
• Worn starter motor brushes or damaged commutator creating erratic electrical pulses during cranking (common on machines with 5,000+ hours)
• Failed or failing starter solenoid contacts producing inconsistent engagement and signal feedback
• Damaged wiring harness between the key switch, starter relay, and ECM—particularly at flex points near the engine mount or chassis frame where vibration causes wire chafing
• Weak or failing batteries that cannot maintain proper voltage during cranking, creating irregular current draw patterns
• ECM relay or starting circuit relay failure causing intermittent power delivery

How to Troubleshoot and Fix Code SPN1667

Step 1: Perform Visual and Connection Inspection Begin with a thorough inspection of all battery cables, terminals, and ground connections. On used excavators, corrosion at battery posts and starter motor mounting bolts is extremely common. Clean all connections with a wire brush and apply dielectric grease. Check the starter motor mounting bolts for tightness, as poor grounding creates irregular signal patterns.

Step 2: Test Battery and Charging System Use a digital multimeter to verify battery voltage (should be 12.4-12.6V at rest, 13.8-14.4V while running). Perform a load test on both batteries to ensure they can maintain at least 9.6V during a 15-second cranking simulation. Weak batteries are a primary cause of irregular pulse width readings.

Step 3: Inspect Starter Motor Wiring Harness Trace the starter motor harness from the ECM through all connection points, paying special attention to areas where the harness contacts the frame, engine block, or hydraulic lines. Look for abraded insulation, crushed wires, or damaged connectors. Use your multimeter to check for resistance (should be less than 0.5 ohms) and continuity in all starter circuit wires.

Step 4: Test Starter Solenoid and Relay Operation With the key in the start position (engine disabled), use a multimeter to verify the solenoid receives full battery voltage (12V+). Listen for a solid "click" indicating proper engagement. Check the starter relay (typically located in the main fuse/relay panel) by swapping it with an identical relay to rule out internal contact failure.

Step 5: Evaluate Starter Motor Performance If all electrical checks pass, the starter motor itself may have internal issues. Perform a no-load current draw test using a clamp ammeter (typical draw: 60-90 amps for Caterpillar starters). Excessive current or erratic readings indicate worn brushes, damaged armature, or bearing problems requiring starter replacement or rebuild.

Step 6: Clear Codes and Monitor After repairs, use Caterpillar Electronic Technician (Cat ET) software or a compatible diagnostic tool to clear the fault code. Perform multiple start cycles while monitoring live data for cranking voltage, starter engagement duration, and signal consistency. For used equipment, establish a baseline for future comparison.

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Disclaimer: This guide provides general troubleshooting information for SPN 1667. Always consult your Caterpillar service manual for model-specific procedures and safety requirements. If you're uncomfortable performing electrical diagnostics, contact a certified Caterpillar technician to prevent further damage to your excavator's electrical system.