Caterpillar 318D2 L Fault Code 39:1658-8: Expert Diagnostic Guide

What is Caterpillar 318D2 L Fault Code 39:1658-8?

Fault Code 39:1658-8 indicates an abnormally high current detected in the hydraulic pump control solenoid circuit, specifically showing a "Current Above Normal" condition in the variable displacement pump control system. This diagnostic trouble code (DTC) is generated by the Electronic Control Module (ECM) when it detects excessive amperage flowing through the pump solenoid, typically exceeding 2.5 amps during operation.

The hydraulic pump control solenoid regulates the swash plate angle in the variable displacement piston pump, directly controlling hydraulic flow and system pressure. On the 318D2 L excavator, this component is critical for managing attachment speed, digging force, and overall hydraulic responsiveness. When this code activates, the ECM may limit pump output to prevent component damage, significantly impacting machine productivity.

Common Symptoms

Operators experiencing this fault code typically report:

• Reduced hydraulic power across all functions (boom, stick, bucket, and swing operations feel sluggish)
• Amber warning light illuminated on the instrument cluster with possible audible alarm
• Derated engine performance as the ECM enters protective mode to prevent system damage
• Inconsistent hydraulic response or "hunting" behavior where functions surge or hesitate
• Increased fuel consumption due to the ECM compensating for perceived hydraulic inefficiencies

Potential Causes

This fault code in used Caterpillar 318D2 L excavators commonly stems from:

• Shorted pump control solenoid winding due to internal coil deterioration (typical after 6,000+ operating hours)
• Damaged wiring harness near the pump mounting area where vibration causes insulation wear and wire-to-ground shorts
• Corroded or moisture-infiltrated connector pins at the X201 pump solenoid connector (known vulnerable point on D2-series machines)
• Failed ECM driver circuit sending excessive voltage to the solenoid (less common but possible in high-hour machines)
• Incorrect solenoid replacement with non-OEM parts having different resistance specifications (should be 10-12 ohms)

How to Troubleshoot and Fix Code 39:1658-8

Step 1: Initial Electrical Verification Using a digital multimeter, disconnect the pump control solenoid connector (located on the main hydraulic pump) and measure solenoid resistance. The correct specification is 10-12 ohms at 20°C (68°F). Readings below 8 ohms indicate a shorted solenoid requiring replacement (Caterpillar part #259-0815).

Step 2: Harness and Connector Inspection Thoroughly inspect the wiring harness routing from the ECM to the pump solenoid, paying special attention to areas where the harness contacts the pump housing or frame rails. On used 318D2 L machines, check for wire insulation damage near the pump mounting bolts—a common rub point. Inspect the X201 connector for green corrosion, bent pins, or moisture intrusion. Clean with electrical contact cleaner and apply dielectric grease.

Step 3: Circuit Current Testing Using Caterpillar Electronic Technician (Cat ET) diagnostic software, monitor real-time solenoid current draw during operation. Normal current should range from 0.8 to 1.5 amps during active control. Readings consistently above 2.0 amps confirm excessive current draw. If the solenoid and harness test properly but high current persists, the ECM output driver may be faulty, requiring ECM replacement or repair.

Step 4: Used Equipment Considerations For used excavators, always check connector seal integrity and look for previous repair attempts (spliced wires, aftermarket connectors). Verify that any replacement solenoid matches OEM specifications—aftermarket solenoids with incorrect impedance can trigger this code even when functioning.

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Disclaimer: This guide provides general diagnostic information for Caterpillar 318D2 L excavators. Always consult the official Caterpillar service manual for your specific machine serial number, and consider professional diagnosis for complex electrical issues. Improper repairs may cause further damage or safety hazards.