Sumitomo Excavator Fault Code P1655: Complete Diagnostic Guide

What is Sumitomo Excavator Fault Code P1655?

Fault Code P1655 indicates a malfunction in the Variable Geometry Turbocharger (VGT) actuator control circuit, specifically detecting an abnormal voltage signal or response from the turbocharger's position control system. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects that the VGT actuator is not responding correctly to commanded positions or is experiencing electrical circuit irregularities.

The VGT system is critical for optimizing engine performance across varying load conditions by adjusting turbine geometry to control boost pressure. When P1655 appears, the ECM typically places the turbocharger into a failsafe "limp mode" position, significantly reducing engine power output and fuel efficiency. For used excavators, this code often indicates age-related electrical degradation or mechanical wear within the turbocharger actuation assembly.

Common Symptoms

When fault code P1655 is active, operators typically experience:

• Significant power loss during digging or lifting operations, with the machine feeling sluggish under load
• Engine warning light illuminated on the instrument cluster, often with audible alert chimes
• Black or gray smoke from the exhaust during acceleration due to improper air-fuel ratios
• Reduced engine RPM ceiling, preventing the machine from reaching normal operating speeds
• Poor throttle response with noticeable lag when attempting to increase engine speed

Potential Causes

The most common technical causes for P1655 on used Sumitomo excavators include:

• Worn or failed VGT actuator motor due to carbon buildup, heat exposure, or internal gear wear
• Damaged wiring harness between the ECM and turbocharger actuator, particularly at flex points near the engine block
• Corroded or loose electrical connectors at the VGT actuator plug, allowing moisture intrusion
• Failed position sensor within the VGT actuator assembly providing incorrect feedback to the ECM
• Stuck or binding VGT vanes caused by excessive soot accumulation preventing proper movement
• ECM internal fault (rare) where the control module cannot properly command the actuator

How to Troubleshoot and Fix Code P1655

Step 1: Visual Inspection and Connector Assessment Begin by locating the VGT actuator on the turbocharger housing. Disconnect the electrical connector and thoroughly inspect both the plug and receptacle for corrosion, bent pins, or oil contamination. On used excavators, this connection point frequently experiences environmental degradation. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: Electrical Circuit Testing Using a digital multimeter, perform resistance checks on the VGT actuator motor windings (typically 10-30 ohms depending on specification). With the ignition on and connector disconnected, back-probe the harness connector to verify the ECM is supplying proper voltage (usually 12V reference). Check for short circuits to ground by measuring resistance between each actuator wire and chassis ground (should read infinite resistance).

Step 3: Actuator Function and Response Testing Reconnect the actuator and use manufacturer-specific diagnostic software (such as Sumitomo's service tool or compatible aftermarket scanners) to command the VGT through its full range of motion. Listen and feel for smooth operation without binding. If the actuator moves but the code persists, the position feedback sensor is likely faulty, requiring actuator replacement.

Step 4: Inspect for Mechanical Binding Remove the actuator from the turbocharger and manually check the VGT linkage for smooth movement. Carbon deposits and soot buildup commonly cause vanes to stick on machines with extended service intervals. Clean thoroughly with appropriate turbocharger cleaner or consider turbocharger removal for comprehensive cleaning if heavily carboned.

Step 5: Harness Routing and Wear Points Trace the entire wiring harness from the actuator to the ECM, paying special attention to areas where the harness contacts the engine block, frame rails, or hydraulic lines. Used excavators often develop harness chafing at mounting brackets. Repair any damaged insulation with high-temperature electrical tape and secure the harness away from moving components.

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Disclaimer: This guide provides general diagnostic information for Sumitomo excavator fault code P1655. Always consult the manufacturer's official service manual for model-specific procedures and specifications. If you're uncomfortable performing electrical diagnostics or turbocharger servicing, contact a qualified heavy equipment technician. Improper repairs may result in engine damage or safety hazards.