Komatsu PC750LC-7 Fault Code E-22: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code E-22?

Fault Code E-22 on the Komatsu PC750LC-7 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically relates to the coolant temperature sensor sending irregular voltage signals or detecting temperatures outside the normal operating parameters.

The ECM relies on accurate coolant temperature data to optimize fuel injection timing, engine protection protocols, and hydraulic system performance. On the PC750LC-7's SAA6D140E-3 engine, maintaining proper temperature monitoring is critical for preventing catastrophic engine damage and ensuring the hydraulic pumps operate within safe thermal limits. When this sensor circuit fails, the machine may enter protective derate mode, significantly impacting productivity.

Common Symptoms

When Code E-22 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with accompanying audible alarm
• Reduced engine power or automatic derate mode limiting RPM to protect the engine
• Erratic temperature gauge readings showing unusually high, low, or fluctuating coolant temperatures
• Hard starting conditions, especially in cold weather, due to incorrect fuel mapping
• Increased fuel consumption as the ECM defaults to rich fuel mixture in failsafe mode

Potential Causes

The most common technical causes for E-22 on used PC750LC-7 excavators include:

• Coolant temperature sensor failure due to age-related degradation or thermal cycling damage
• Wiring harness damage at known rub points near the engine block or along the chassis rail
• Corroded or loose connector pins at the sensor plug, especially on machines operating in harsh environments
• ECM internal fault affecting the sensor input circuit (less common but possible on high-hour machines)
• Coolant system issues causing actual overheating that triggers legitimate sensor readings
• Ground circuit problems creating voltage reference errors in the sensor signal

How to Troubleshoot and Fix Code E-22

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for obvious damage, chafing, or oil contamination. Check the connector for corrosion, bent pins, or moisture intrusion—common issues on used excavators with 5,000+ hours.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult Komatsu service manual for exact specifications). Test the harness voltage with the key on, engine off—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Signal Testing Reconnect the sensor and use Komatsu diagnostic software (KOMTRAX) or a compatible scan tool to monitor live coolant temperature data. Compare readings with an infrared thermometer measurement of actual coolant temperature. A variance greater than 10°F indicates sensor replacement is necessary.

Step 4: Harness and Ground Verification Inspect the ground circuit continuity between the sensor ground pin and chassis ground. Resistance should be less than 1 ohm. On used machines, check for harness wear at the engine mount area where vibration causes insulation breakdown.

Step 5: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu coolant temperature sensor (Part #6732-81-3210 or equivalent). After installation, clear codes using diagnostic software and perform a test cycle to verify proper operation.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.