Caterpillar Fault Code 5704: Diagnostic Guide for Used Excavators

What is Caterpillar Fault Code 5704?

Caterpillar Fault Code 5704 indicates an Abnormal Update Rate for the Engine Control Module (ECM). This diagnostic trouble code (DTC) signals that the ECM is not receiving or processing data from critical sensors at the expected frequency, causing communication errors within the machine's electronic control system.

This fault typically affects Caterpillar excavators equipped with ACERT or C-Series diesel engines, where the ECM relies on continuous data streams from multiple sensors to optimize fuel injection, boost pressure, and emissions control. When the update rate falls outside manufacturer specifications, the ECM enters a protective mode that may limit engine performance to prevent potential damage. For used excavators, this code often emerges due to aging electrical components, corroded connections, or CAN bus communication failures that develop over thousands of operating hours.

Common Symptoms

When Code 5704 is active, operators typically experience:

• Check Engine light or malfunction indicator illuminated on the instrument panel
• Engine derate or reduced power output, limiting machine productivity
• Intermittent loss of throttle response or uneven engine performance
• Display errors on the monitor screen showing communication faults
• Difficulty starting or rough idle conditions in cold weather

Potential Causes

The most common technical reasons for Code 5704 on used Caterpillar excavators include:

• Faulty ECM wiring harness with damaged insulation, particularly at known rub points near the engine block or hydraulic pump mounting areas
• Corroded or loose ECM connectors, especially the main 70-pin or 120-pin harness connections exposed to moisture
• Failed crankshaft position sensor or camshaft position sensor providing erratic signal data
• Low battery voltage or weak alternator output causing voltage drops during ECM processing cycles
• Degraded ECM itself, common in machines with 8,000+ operating hours
• CAN bus termination resistor failure or open circuit in the data link network
• Incompatible ECM software following previous repairs or flash updates

How to Troubleshoot and Fix Code 5704

Step 1: Connect Diagnostic Software Use Caterpillar Electronic Technician (Cat ET) software with a compatible communication adapter. Check active and logged fault codes, then monitor live ECM data to identify which sensor signals are missing or showing abnormal update rates.

Step 2: Inspect Electrical Connections For used excavators, visually inspect all ECM harness connectors for corrosion, bent pins, or moisture intrusion. Pay special attention to connectors near heat sources or areas with cable movement. Clean contacts with electrical contact cleaner and apply dielectric grease. Check known wear points where harnesses contact the frame or engine components.

Step 3: Test Sensor Inputs Using a digital multimeter, verify voltage supply (typically 5V or 8V reference) to critical sensors including the crankshaft position sensor, camshaft sensor, and fuel pressure sensor. Check resistance values against manufacturer specifications found in the service manual for your specific engine model.

Step 4: Verify Power Supply Measure battery voltage (should be 12.5-13V minimum) and alternator output during operation (13.8-14.4V). Test ECM power and ground circuits for voltage drop; ground circuits should show less than 0.1V drop under load.

Step 5: Check CAN Bus Integrity Measure resistance between CAN High and CAN Low terminals at the ECM connector (should read 55-65 ohms with key off, indicating proper termination). Inspect datalink connectors for damage or corrosion that could cause intermittent communication failures.

Step 6: Clear Codes and Test After repairs, clear fault codes using Cat ET software and operate the machine under normal load. Monitor for code recurrence while observing ECM data stream quality.

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Disclaimer: This guide provides general diagnostic information for Caterpillar fault code 5704. Always consult your machine's specific service manual and consider professional assistance from certified Caterpillar technicians for complex electrical diagnostics. Improper troubleshooting may result in further damage to electronic components.