Case CX210C Fault Code 687: Complete Diagnostic Guide

What is Case CX210C Fault Code 687?

Fault Code 687 on the Case CX210C excavator indicates a "Hydraulic Oil Temperature Sensor Circuit High Voltage" condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the hydraulic oil temperature sensor, typically above 4.5 volts when normal operating range should be 0.5-4.5 volts.

This code directly impacts the machine's ability to monitor and protect the hydraulic system from overheating damage. The Case CX210C relies on accurate temperature readings to prevent component failure, maintain optimal hydraulic fluid viscosity, and trigger appropriate cooling responses. When this sensor circuit malfunctions, the ECM cannot accurately assess system health, potentially leading to costly hydraulic pump or motor damage.

Common Symptoms

When Code 687 is active on your CX210C, operators typically experience:

• Hydraulic temperature warning light illuminated on the instrument cluster
• Derated engine power or limited hydraulic function as the ECM enters protective mode
• Inaccurate temperature gauge readings showing abnormally high or fluctuating temperatures
• Intermittent code activation during cold starts or machine operation
• Error messages on the digital display indicating hydraulic system faults

Potential Causes

The most common technical causes for Code 687 on used CX210C excavators include:

• Open circuit in sensor wiring harness due to chafing against frame components near the hydraulic tank
• Corroded or damaged sensor connector pins from exposure to moisture and hydraulic fluid contamination
• Failed hydraulic oil temperature sensor with internal short circuit (common after 5,000+ operating hours)
• Damaged ECM sensor input circuit from previous electrical surges or improper jump-starting
• Broken or stretched sensor signal wire in the harness routing near the swing bearing
• Poor ground connection at the sensor mounting location due to rust buildup on used machines

How to Troubleshoot and Fix Code 687

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor mounted on the hydraulic tank (typically on the left side near the return filter). Inspect the wiring harness for obvious damage, particularly where it routes along the frame rails. On used excavators, check for wire insulation wear from rubbing, corroded connectors, and loose mounting bolts that could cause intermittent ground issues.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Next, check for continuity between sensor signal wire and ground—any continuity indicates a short circuit. Measure voltage at the ECM connector with ignition on; you should see approximately 5 volts reference voltage on the signal wire.

Step 3: Component Replacement and Verification If sensor resistance is out of specification or the circuit shows high voltage with the sensor disconnected, replace the hydraulic oil temperature sensor (Case part number varies by serial number). Before installation on used machines, clean the mounting threads with a wire brush and apply anti-seize compound. Clear the fault code using Case diagnostic software or a compatible scan tool, then operate the machine through a complete warm-up cycle to verify proper sensor function and code elimination.

Disclaimer: This guide provides general diagnostic procedures for experienced technicians. Always consult the official Case service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if you're uncomfortable performing these procedures.