Caterpillar 320D2 Fault Code 39:1598-6: Complete Diagnostic Guide

What is Caterpillar 320D2 Fault Code 39:1598-6?

Fault Code 39:1598-6 indicates a "Pump Solenoid Circuit - Current Below Normal" condition in the Caterpillar 320D2 excavator's hydraulic system. This code is triggered when the Electronic Control Module (ECM) detects insufficient electrical current flowing through the main pump control solenoid circuit, falling below the manufacturer's specified threshold.

This fault directly impacts the hydraulic pump's ability to regulate flow and pressure. The 320D2 relies on precise electronic control of its variable displacement pump to optimize fuel efficiency and hydraulic performance. When current drops below normal parameters, the ECM cannot properly modulate pump output, potentially causing reduced machine productivity and increased fuel consumption. This is particularly critical in used machines where electrical connections and solenoid windings may have degraded over thousands of operating hours.

Common Symptoms

When fault code 39:1598-6 is active, operators typically experience:

• Reduced hydraulic power across all functions, with noticeably slower boom, arm, or bucket movements
• Intermittent or constant amber warning light on the instrument cluster
• Engine derating or inability to achieve full RPM under load
• Erratic hydraulic response, where the machine alternates between normal and reduced power
• Increased fuel consumption as the ECM defaults to failsafe pump settings

Potential Causes

The most common technical reasons for this fault code on used Caterpillar 320D2 excavators include:

• Damaged pump solenoid winding causing increased resistance or partial short circuit
• Corroded or loose connector pins at the pump solenoid harness (common failure point after 5,000+ hours)
• Chafed wiring harness near the main pump mounting area where vibration causes insulation wear
• Failed ECM driver circuit unable to supply adequate current to the solenoid
• High resistance ground connection at the pump assembly mounting point
• Contaminated solenoid coil from hydraulic fluid intrusion through worn seals

How to Troubleshoot and Fix Code 39:1598-6

Step 1: Visual Inspection Begin by inspecting the pump solenoid connector located on the main hydraulic pump. Disconnect the harness and examine pins for corrosion, oil contamination, or bent contacts. On used excavators, this connector frequently accumulates moisture and debris. Clean with electrical contact cleaner and dielectric grease.

Step 2: Resistance Testing Using a digital multimeter, measure the solenoid coil resistance across the solenoid terminals. Caterpillar specifications typically call for 3-7 ohms (verify with service manual). Readings below 2 ohms indicate a short circuit; readings above 10 ohms suggest coil degradation requiring solenoid replacement.

Step 3: Wiring Harness Continuity Check Trace the harness from ECM to pump solenoid, inspecting for wear points where cables contact the pump housing or chassis. Check continuity and resistance on both power and ground circuits. Pay special attention to the harness routing near the swing bearing where flexing causes conductor breakage in high-hour machines.

Step 4: Current Draw Testing With the solenoid connected and engine running, use a clamp ammeter to measure actual current flow during pump operation. Compare against specification (typically 0.8-1.5 amps). Lower readings confirm insufficient current supply, pointing to ECM driver issues or excessive circuit resistance.

Step 5: ECM and Ground Verification Verify the pump ground circuit has less than 0.5 ohms resistance to battery negative. Check ECM connector pins for corrosion or terminal tension loss. On used machines, ECM connectors often require cleaning and pin retention adjustment.

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Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Caterpillar service manual for your specific machine serial number. Hydraulic system repairs involve high-pressure components and electrical diagnostics require proper training. If unsure, consult a certified Caterpillar technician to prevent equipment damage or injury.