Caterpillar 735 Articulated Truck Fault Code 585-8: Complete Diagnostic Guide

What is Caterpillar 735 Fault Code 585-8?

Fault Code 585-8 indicates "Transmission Clutch Pressure Sensor 2 - Abnormal Frequency, Pulse Width, or Period." This code triggers when the Electronic Control Module (ECM) detects an irregular signal pattern from the transmission clutch pressure sensor responsible for monitoring hydraulic pressure in the clutch pack circuits.

This code is critical for the Caterpillar 735 [3F5] articulated hauler because the transmission control system relies on precise pressure readings to execute smooth gear shifts and maintain optimal torque converter lockup. When this sensor provides erratic signals, the ECM cannot accurately control clutch engagement, potentially causing transmission damage or complete derate to protect the drivetrain.

Common Symptoms

When fault code 585-8 is active, operators typically experience:

• Transmission warning lamp illuminated on the dash display
• Harsh or delayed shifting between gears, particularly under load
• Transmission derate mode limiting machine speed to protect components
• Intermittent loss of power during acceleration or grade climbing
• Erratic gear hunting where the transmission shifts unexpectedly between ranges

Potential Causes

The most common technical causes for this fault code on used Caterpillar 735 machines include:

• Damaged or corroded sensor connector at the transmission housing (common failure point due to heat and vibration exposure)
• Worn wiring harness with insulation breakdown from rubbing against the transmission bell housing
• Failed clutch pressure sensor (internal circuit degradation from thermal cycling)
• Contaminated transmission fluid causing sensor fouling or erratic pressure readings
• ECM software glitch or corrupted calibration files (less common but possible on older machines)
• Intermittent short to ground in the sensor circuit wiring

How to Troubleshoot and Fix Code 585-8

Step 1: Visual Inspection Begin by inspecting the clutch pressure sensor connector located on the transmission case. Look for corrosion, bent pins, moisture intrusion, or oil contamination. On used excavators, check the wiring harness routing for signs of chafing against metal edges or heat damage from exhaust components.

Step 2: Electrical Testing Using a digital multimeter, perform resistance and voltage checks on the sensor circuit. With ignition on and engine off, verify 5-volt reference voltage at the sensor connector. Check sensor resistance (typically 500-2500 ohms depending on temperature). Use Caterpillar Electronic Technician (CAT ET) diagnostic software to monitor live sensor frequency and pulse width data.

Step 3: Component Replacement If sensor readings are erratic or out of specification, replace the clutch pressure sensor using genuine Caterpillar parts. Before installation, clean the mounting surface and apply appropriate thread sealant. Clear codes and perform a transmission calibration procedure using CAT ET software.

Disclaimer: This guide provides general diagnostic information. Always consult factory service manuals and consider professional technician assistance for complex transmission repairs.