What is Kobelco SK135SRLC-2 Fault Code A235?

Fault Code A235 on the Kobelco SK135SRLC-2 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal temperature reading detected by the Engine Control Module (ECM). This code typically triggers when the ECM receives voltage signals outside the expected range from the coolant temperature sensor, suggesting either a sensor failure, wiring issue, or actual overheating condition.

The coolant temperature sensor is critical for the SK135SRLC-2's performance because it directly influences fuel injection timing, engine warm-up cycles, and overheat protection protocols. When this sensor fails or provides inaccurate data, the ECM cannot properly manage engine temperature, potentially leading to reduced performance, increased fuel consumption, or catastrophic engine damage if genuine overheating goes undetected.

Common Symptoms

When Code A235 is active on your Kobelco SK135SRLC-2, operators typically experience:

• Engine warning light or check engine lamp illuminated on the instrument cluster
• Engine operating in derate mode (reduced power output) as a protective measure
• Difficult cold starts or extended warm-up periods due to improper fuel mapping
• Engine cooling fan running continuously at high speed regardless of actual temperature
• Erratic temperature gauge readings or gauge stuck at cold/hot extremes

Potential Causes

The most common technical causes for Code A235 on used Kobelco SK135SRLC-2 excavators include:

• Coolant temperature sensor failure due to age-related internal resistance drift or contamination from degraded coolant
• Wiring harness damage near the thermostat housing where vibration and heat cause insulation breakdown and short circuits
• Corroded or loose connector pins at the sensor plug, common in machines with 5,000+ operating hours
• Low coolant levels causing air pockets around the sensor, resulting in false high-temperature readings
• ECM internal fault (rare) where the temperature input circuit has failed
• Aftermarket or incorrect sensor replacement with incompatible resistance specifications

How to Troubleshoot and Fix Code A235

Step 1: Visual Inspection and Initial Checks Begin by inspecting coolant levels when the engine is cold. Check for visible leaks around the radiator, hoses, and water pump. Examine the coolant temperature sensor (typically located near the thermostat housing on the cylinder head) and its wiring harness for obvious damage, corrosion, or oil contamination. On used excavators, pay special attention to harness routing where it contacts metal edges or moves with engine vibration.

Step 2: Electrical Testing of the Sensor Circuit Disconnect the coolant temperature sensor connector and use a digital multimeter to measure sensor resistance. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult Kobelco service manual for exact specifications). Test harness continuity from the sensor connector back to the ECM pins—resistance should be less than 5 ohms. Check for shorts to ground by measuring resistance between each wire and chassis ground (should read infinite/open circuit).

Step 3: Voltage Supply Verification With the ignition on but engine off, measure reference voltage at the sensor connector from the ECM—this should be approximately 5 volts. If voltage is absent or significantly different, trace the wiring for breaks or investigate potential ECM issues. For used machines, connector corrosion is frequently the culprit; clean terminals with electrical contact cleaner and apply dielectric grease.

Step 4: Component Replacement and Verification If sensor resistance is out of specification or wiring tests reveal faults, replace the defective component with genuine Kobelco parts to ensure proper resistance curves match ECM programming. After replacement, clear the fault code using Kobelco diagnostic software or by disconnecting the battery for 10 minutes. Run the engine through a complete heat cycle while monitoring for code reoccurrence and verifying accurate gauge readings.

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Disclaimer: This guide provides general troubleshooting information for Kobelco SK135SRLC-2 excavators. Always consult the official Kobelco service manual and consider professional diagnostic assistance for complex electrical issues. Improper diagnosis may lead to unnecessary part replacement or undetected engine damage.