Caterpillar 318D2 Fault Code 39:1598-6: Complete Diagnostic Guide

What is Caterpillar 318D2 Fault Code 39:1598-6?

Fault Code 39:1598-6 indicates a voltage problem (moderately high) with the Diesel Particulate Filter (DPF) Differential Pressure Sensor circuit on the Caterpillar 318D2 excavator. This diagnostic trouble code (DTC) signals that the Electronic Control Module (ECM) has detected an abnormally high voltage reading from the pressure sensor that monitors exhaust backpressure across the DPF.

The DPF differential pressure sensor measures the restriction level in the diesel particulate filter by comparing inlet versus outlet pressures. This data is critical for the ECM to determine when regeneration cycles are needed and to protect the engine from excessive backpressure. On used excavators like the 318D2, this code can trigger emissions-related performance limitations and prevent proper filter regeneration, potentially causing costly DPF damage if ignored.

Common Symptoms

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

• Amber warning lamp illuminated on the instrument cluster with possible "Check Engine" message
• Forced regeneration inability – the system may not complete automated DPF cleaning cycles
• Engine derate or power reduction in some cases, especially if the fault persists
• Inaccurate DPF status readings displayed on the monitor showing incorrect soot loading percentages
• Increased fuel consumption due to improper regeneration management

Potential Causes

The most common technical causes for this voltage-related fault include:

• Damaged or corroded wiring harness between the DPF pressure sensor and ECM – particularly at known rub points near the exhaust system
• Failed DPF differential pressure sensor with internal short circuit causing high voltage output
• Contaminated or corroded connector pins at the sensor or ECM due to moisture intrusion (common on used machines)
• Shorted signal wire in the harness providing constant high voltage to the ECM
• Faulty ECM (rare) with internal circuit problems reading sensor voltage incorrectly
• Aftermarket or incorrect sensor replacement with incompatible voltage specifications

How to Troubleshoot and Fix Code 39:1598-6

Step 1: Visual Inspection Begin with a thorough inspection of the DPF pressure sensor located on the exhaust system. Check the wiring harness for signs of heat damage, abrasion, or melting near hot exhaust components. On used 318D2 excavators, inspect connector pins for corrosion, bent terminals, or moisture. Clean connectors with electrical contact cleaner and dielectric grease.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the pressure sensor connector and measure resistance across sensor terminals (typically 1,000-3,000 ohms at room temperature – consult service manual for exact specs). Check signal wire voltage with the key on, engine off; it should read approximately 5 volts reference voltage. Measure circuit resistance from sensor connector to ECM – readings above 5 ohms indicate wiring issues.

Step 3: Sensor and Harness Verification If voltage readings exceed specifications (typically above 4.8V on the signal wire with sensor connected), suspect a shorted sensor or harness. Disconnect the sensor and recheck voltage; if it drops to normal, replace the sensor. If voltage remains high, trace and repair the harness short circuit. For used excavators, pay special attention to harness routing near moving parts or heat shields where insulation degrades over time.

Step 4: Component Replacement and Validation Replace faulty components with genuine Caterpillar parts when possible. After repairs, clear codes using Caterpillar Electronic Technician (Cat ET) diagnostic software and perform a stationary regeneration to verify proper sensor operation. Monitor live data to confirm pressure readings respond correctly during regeneration cycles.

Disclaimer: This guide provides general diagnostic information. Always consult the official Caterpillar service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues or if you lack proper tools and training.