What is Sumitomo General Fault Code 42?

Fault Code 42 on Sumitomo excavators indicates a Throttle Position Sensor (TPS) Circuit Malfunction or Signal Error. This diagnostic trouble code is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal or erratic readings from the throttle position sensor, which monitors the position of the throttle lever and communicates engine load demands to the control system.

The TPS is critical for proper engine performance on Sumitomo excavators because it directly influences fuel delivery, engine RPM control, and hydraulic pump output. When this sensor fails or sends incorrect data, the ECM cannot properly regulate engine speed, leading to reduced operational efficiency and potential safety concerns. In used machines, this code often results from sensor degradation, connector corrosion, or wiring harness damage accumulated over thousands of operating hours.

Common Symptoms

• Erratic engine RPM fluctuations or inability to maintain consistent throttle settings, even when the operator holds the lever steady
• Engine warning light illuminated on the instrument panel, potentially accompanied by reduced engine power or hydraulic response
• Sudden engine derating or failure to reach full throttle, limiting digging force and cycle times
• Rough idling or stalling when attempting to increase throttle from low idle positions
• Poor hydraulic response during combined operations due to improper engine-pump matching

Potential Causes

The most common technical causes for Code 42 on used Sumitomo excavators include:

• Worn or failed throttle position sensor due to age, vibration, or internal potentiometer track degradation
• Corroded or loose electrical connectors at the TPS or ECM harness connections, especially on machines operating in humid or marine environments
• Damaged wiring harness with broken wires, chafing, or shorts to ground—particularly at known rub points near the engine mounting brackets or throttle linkage
• Poor ground connections at the sensor or ECM mounting locations causing voltage reference errors
• ECM calibration drift or internal faults (less common but possible in high-hour used machines)
• Water intrusion into the sensor housing or connector seals compromising signal integrity

How to Troubleshoot and Fix Code 42

Step 1: Visual Inspection Begin by thoroughly inspecting the throttle position sensor mounting location and all associated wiring. Check for obvious physical damage, loose connectors, or corrosion on terminals. On used excavators, pay special attention to harness routing near moving components where friction wear commonly occurs.

Step 2: Electrical Testing Using a digital multimeter, measure the TPS output voltage at the sensor connector with the ignition on (engine off). Typical specifications show approximately 0.5-1.0V at closed throttle and 4.0-4.5V at full throttle. Slowly move the throttle lever while monitoring voltage—any jumps, dropouts, or irregular progression indicate sensor failure. Also verify the 5V reference voltage supply from the ECM and check for proper ground continuity (less than 1 ohm resistance).

Step 3: Connector and Harness Verification Disconnect the TPS connector and inspect for moisture, corrosion (green/white deposits), or bent pins. Clean contacts with electrical contact cleaner and apply dielectric grease. Perform a wiggle test on the harness while monitoring resistance to identify intermittent opens or shorts.

Step 4: Component Replacement If testing confirms sensor failure, replace the throttle position sensor with a genuine or OEM-equivalent part. After installation, clear fault codes using Sumitomo diagnostic software or a compatible scan tool, then perform a throttle relearn procedure if required by your specific model.

Step 5: Post-Repair Verification Operate the excavator through various throttle positions and load conditions to ensure Code 42 does not return. Monitor live data streams to confirm smooth TPS voltage transitions.

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Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual for your specific Sumitomo model and consider professional diagnostic assistance for complex electrical issues, especially on used equipment with unknown service history.