What is Caterpillar Fault Code EID1585?

Fault Code EID1585 indicates an Exhaust Temperature Sensor Circuit malfunction in Caterpillar excavators and heavy equipment. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormal voltage reading from the Exhaust Gas Temperature (EGT) sensor, typically indicating an open circuit, short circuit, or sensor malfunction within the aftertreatment system.

This code is critical for machines equipped with Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) systems. The EGT sensor monitors exhaust temperatures to ensure proper regeneration cycles and prevent thermal damage to aftertreatment components. Ignoring this fault can lead to incomplete DPF regeneration, reduced engine performance, and potential component failure in the exhaust system.

Common Symptoms

When EID1585 is active, operators may experience:

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the dashboard
• Engine derate or power reduction mode to protect aftertreatment components
• Failed or incomplete DPF regeneration cycles, leading to increased soot accumulation
• Excessive exhaust smoke (black or white) due to improper regeneration management
• Error messages on the instrument cluster indicating exhaust system faults

Potential Causes

The most common technical reasons for EID1585 on used Caterpillar excavators include:

• Faulty Exhaust Gas Temperature Sensor due to prolonged heat exposure or carbon buildup
• Damaged wiring harness or corroded connectors near the exhaust manifold (common rub points on aged machines)
• Open or short circuit in the EGT sensor circuit between the sensor and ECM
• Contaminated or broken sensor connector pins from moisture, oil, or exhaust gas infiltration
• ECM internal fault (less common, but possible in high-hour machines)
• Aftermarket or incorrect sensor replacement with improper resistance specifications

How to Troubleshoot and Fix Code EID1585

Step 1: Visual Inspection Begin by inspecting the EGT sensor and its wiring harness near the exhaust manifold and DPF. Look for melted insulation, frayed wires, corrosion on connectors, or physical damage. On used excavators, check known harness rub points where the wiring contacts frame members or moving components.

Step 2: Electrical Testing Using a digital multimeter (DMM), check the resistance of the EGT sensor (typically 100-200 ohms at room temperature, but verify with Caterpillar specifications). Disconnect the sensor connector and measure continuity through the harness to the ECM. Check for short circuits to ground by measuring resistance between each circuit wire and chassis ground (should read infinite resistance).

Step 3: Voltage Signal Check With the ignition on and sensor connected, use Caterpillar Electronic Technician (Cat ET) diagnostic software to monitor live EGT sensor voltage. Normal readings typically range from 0.5V to 4.5V depending on temperature. Out-of-range readings confirm sensor or circuit failure.

Step 4: Component Replacement If testing confirms sensor failure, replace the EGT sensor with genuine Caterpillar parts to ensure proper resistance values. If harness damage is found, repair using heat-resistant, sealed connectors and reroute away from heat sources. Clear the fault code using diagnostic software and perform a test regeneration cycle to verify repair.

Critical for Used Equipment: Before replacing expensive components, thoroughly inspect all connector seals and clean corrosion with electrical contact cleaner. Many EID1585 codes on older machines resolve with proper harness repair and connector maintenance.

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Disclaimer: This guide provides general troubleshooting information. Always consult Caterpillar service manuals and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional damage or safety hazards.