Sumitomo SH240-6 Fault Code 122: Expert Diagnosis and Repair Guide

What is Sumitomo SH240-6 Fault Code 122?

Fault Code 122 on the Sumitomo SH240-6 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) sensor circuit, specifically signaling a high voltage condition or open circuit in the sensor wiring harness. This diagnostic trouble code (DTC) is generated when the Engine Control Module (ECM) detects voltage readings above the normal operating range (typically above 4.8V) from the coolant temperature sensor.

The ECT sensor plays a critical role in engine management by providing real-time coolant temperature data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine protection protocols. On used SH240-6 excavators, this code can trigger protective measures that limit machine performance to prevent potential engine damage.

Common Symptoms

When Code 122 is active, operators typically experience:

• Hard starting or rough idle, especially during cold starts when the ECM cannot properly adjust fuel mixture
• Check Engine light illuminated on the instrument panel with possible temperature gauge reading abnormally low or fluctuating erratically
• Engine derate mode activation, limiting maximum RPM and hydraulic system performance
• Increased fuel consumption due to the ECM defaulting to a failsafe enriched fuel map
• White or black exhaust smoke indicating improper combustion from incorrect temperature compensation

Potential Causes

The most common technical failures triggering Code 122 on used SH240-6 excavators include:

• Open circuit in the ECT sensor wiring harness, particularly at known rub points near the engine block and firewall where vibration causes insulation breakdown
• Failed ECT sensor with internal open circuit (common after 5,000+ operating hours)
• Corroded or loose connector terminals at the sensor plug, especially on machines operated in wet or marine environments
• Damaged ECM wiring between the sensor connector and the control module
• ECM internal fault (less common) affecting the 5V reference voltage supply circuit

How to Troubleshoot and Fix Code 122

Step 1: Visual Inspection Begin by locating the ECT sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, check the entire wiring harness from sensor to ECM for chafing, particularly where it contacts metal brackets or passes through rubber grommets.

Step 2: Electrical Testing Disconnect the ECT sensor connector. Using a digital multimeter, measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,400-2,700 ohms. Next, check for continuity in the harness wiring from the sensor connector back to the ECM pins. Resistance should be less than 5 ohms per wire.

Step 3: Reference Voltage Check With the ignition on and sensor disconnected, measure voltage at the harness connector. You should see approximately 5V reference voltage on one terminal. If voltage is absent or incorrect, suspect ECM issues or a break in the reference circuit.

Step 4: Component Replacement If the sensor tests faulty (out-of-range resistance), replace it with an OEM-equivalent ECT sensor and apply dielectric grease to connector terminals. For used machines with harness damage, repair or replace the affected wiring section using proper gauge wire and heat-shrink connectors.

Step 5: Clear Code and Verify After repairs, clear the fault code using diagnostic software or by disconnecting the battery for 30 seconds. Run the engine through multiple temperature cycles and recheck for code recurrence.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Sumitomo SH240-6 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause further damage or safety hazards.