Sumitomo SH80-6B Fault Code P0124-2: Complete Diagnostic Guide

What is Sumitomo SH80-6B Fault Code P0124-2?

Fault Code P0124-2 indicates a Throttle Position Sensor (TPS) "A" Circuit Intermittent/Erratic signal detected by the Engine Control Module (ECM). This code specifically means the ECM has registered an inconsistent or unstable voltage signal from the TPS, which monitors the accelerator pedal position and controls engine speed output.

On the Sumitomo SH80-6B excavator, the Throttle Position Sensor is critical for precise engine control and hydraulic system responsiveness. The sensor sends analog voltage signals (typically 0.5-4.5V) to the ECM, which then adjusts fuel delivery and engine RPM accordingly. When intermittent signals occur, the machine's performance becomes unpredictable, potentially causing safety hazards and reduced productivity on job sites.

This fault is particularly important because the SH80-6B's hydraulic pump output is directly tied to engine speed regulation—erratic TPS signals compromise both digging force and swing speed consistency.

Common Symptoms

When Code P0124-2 is active on your Sumitomo SH80-6B, operators typically experience:

• Intermittent engine surging or hunting at idle or under load, with RPMs fluctuating unexpectedly
• Check Engine Light (CEL) illuminated on the instrument panel, possibly with accompanying warning beeps
• Inconsistent throttle response when operating the accelerator dial or pedal—engine may not respond proportionally to input
• Sudden loss of power or derate mode where the ECM limits engine output to prevent potential damage
• Hydraulic function delays or sluggishness during combined operations due to inconsistent engine speed control

Potential Causes

The most common technical causes for P0124-2 on used Sumitomo excavators include:

• Worn or corroded TPS connector terminals—especially common in machines with 5,000+ operating hours exposed to moisture and vibration
• Damaged wiring harness between the TPS and ECM, particularly at known rub points near the engine mount brackets or along the right-side frame rail
• Failed Throttle Position Sensor itself, with internal potentiometer wear causing intermittent resistance changes
• Poor ground connections at the sensor mounting location or ECM ground points (check engine block ground straps)
• ECM voltage supply issues—the 5V reference circuit may have intermittent faults due to internal ECM component aging
• Mechanical throttle linkage binding or sticking, causing rapid position changes that register as electrical faults

How to Troubleshoot and Fix Code P0124-2

Step 1: Visual and Physical Inspection

Begin by inspecting the TPS connector located on the engine's fuel injection pump or throttle body assembly. Disconnect the connector and examine pins for corrosion, bent terminals, or moisture intrusion—common in used excavators. Check the wiring harness routing from the TPS along the engine compartment, looking for chafing against metal edges, particularly where harnesses pass near the hydraulic pump or starter motor.

Step 2: Electrical Testing with Multimeter

Using a digital multimeter (DMM), perform voltage and resistance checks:

• With ignition ON, engine OFF, backprobe the TPS signal wire (consult wiring diagram for specific pin)—you should see approximately 0.5-0.8V at idle position
• Slowly actuate the throttle while monitoring voltage; it should sweep smoothly from ~0.5V to ~4.5V without jumps or dropouts
• Check the 5V reference voltage supply from the ECM to the TPS—should read 4.8-5.2V consistently
• Measure sensor ground circuit resistance to chassis ground—should be less than 1 ohm

Step 3: Component Testing and Replacement

If voltage readings are erratic, disconnect the TPS and measure internal resistance across sensor terminals while manually rotating the shaft. Resistance should change smoothly (typically 1-5kΩ range) without sudden spikes. For used excavators, even if readings seem acceptable, connector corrosion often causes intermittent contact—clean terminals with electrical contact cleaner and apply dielectric grease.

Step 4: Harness and ECM Verification

If the TPS tests good, inspect the harness continuity from sensor to ECM connector using a wiring diagram. Wiggle test the harness while monitoring voltage to identify intermittent breaks. Check ECM connector terminals for corrosion or backing-out pins. On higher-hour machines, ECM internal failures can cause reference voltage instability—this requires diagnostic software like Sumitomo's SCS diagnostic tool to monitor live data parameters.

Critical for Used Equipment: Before replacing the TPS (approximately $150-$300 part), always address connector condition and harness routing. Many P0124-2 codes on older excavators resolve simply by repairing corroded connections or relocating harnesses away from heat/friction sources.

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Disclaimer: This guide provides general troubleshooting information for Code P0124-2. Always consult the Sumitomo SH80-6B service manual for model-specific procedures, torque specifications, and safety precautions. If you're uncomfortable with electrical diagnostics, contact a certified heavy equipment technician to prevent further damage or safety risks.