What is Case CX210C Fault Code P0687?

Fault Code P0687 indicates an ECM/PCM Power Relay Control Circuit Low condition in your Case CX210C excavator. This diagnostic trouble code (DTC) means the Engine Control Module (ECM) has detected abnormally low voltage or an open circuit in the power relay control circuit that manages electrical power distribution to critical engine systems.

The ECM power relay acts as the electrical gatekeeper for your excavator's diesel engine management system. When this circuit fails, the ECM cannot properly control fuel injection timing, sensor power supply, or other vital engine functions. For the CX210C with its Isuzu 6HK1X engine, this fault can prevent startup or cause immediate shutdown, as the ECM loses its ability to maintain stable power delivery to fuel solenoids and sensor networks.

Common Symptoms

• No-start condition or engine cranks but immediately shuts down after brief startup
• ECM warning light illuminated on the instrument cluster with possible loss of other digital displays
• Intermittent power loss to dashboard gauges and engine sensors during operation
• Unexpected engine shutdown during normal working conditions, particularly under load
• Difficulty restarting after the machine has been sitting, requiring multiple attempts

Potential Causes

The P0687 code in used CX210C excavators typically stems from age-related electrical degradation. The main power relay itself frequently fails due to contact wear after thousands of operating hours. Corroded or loose connections at the relay socket are extremely common, especially in machines exposed to moisture or stored outdoors.

Wiring harness damage near the ECM mounting location is another frequent culprit—vibration causes wire insulation to rub against the frame, creating intermittent shorts or opens. The ECM ground connections can also corrode over time, causing the control circuit to read incorrectly low. In some cases, the ECM internal driver circuit for the relay may have failed, though this is less common than external wiring issues.

How to Troubleshoot and Fix Code P0687

Step 1: Locate the ECM power relay in the main fuse/relay panel (typically under the right-hand side panel near the operator's cab). With the key off, remove the relay and inspect for burned contacts, corrosion, or loose pins. Check the relay socket for damaged terminals or moisture intrusion.

Step 2: Using a digital multimeter, test the relay itself. Check for continuity between terminals 85 and 86 (coil resistance should be 70-90 ohms). Apply 12V to the coil terminals and verify terminals 30 and 87 show continuity when energized.

Step 3: Inspect the wiring harness from the ECM to the relay socket. Look for worn insulation, particularly where harnesses route over the frame rail. Check all ground connections at the ECM mounting bracket—clean and retighten with dielectric grease.

Step 4: With a diagnostic laptop running CNH EST software, monitor live relay command data while cycling the key. The ECM should command the relay ON during cranking. If commanded but voltage remains low, replace the relay and recheck connections.

For used excavators, always inspect connector pin tension and apply electrical contact cleaner before replacing components—corrosion is often the root cause in older machines.

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Disclaimer: This guide provides general troubleshooting information. Always consult a certified Case technician or the official service manual for your specific machine. Improper electrical diagnostics can damage the ECM or create safety hazards.