Komatsu PC800SE-7 Fault Code E112: Complete Diagnostic Guide

What is Komatsu PC800SE-7 Fault Code E112?

Fault Code E112 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 outside the manufacturer's specified parameters, typically between 0.5-4.5 volts.

For the Komatsu PC800SE-7's SAA6D170E-7 engine, accurate coolant temperature monitoring is critical for proper fuel injection timing, engine protection systems, and hydraulic oil temperature management. When this sensor fails, the ECM cannot properly regulate engine performance, potentially leading to overheating, reduced power output, or unnecessary engine derates that impact productivity on job sites.

Common Symptoms

When Code E112 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with possible audible alarm
• Engine derate mode activated, limiting maximum RPM to protect components
• Difficulty starting in cold conditions or extended cranking times
• Cooling fan running continuously at high speed regardless of actual temperature
• Inaccurate temperature gauge readings (stuck at cold, hot, or fluctuating erratically)

Potential Causes

The most common technical causes for E112 on used PC800SE-7 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal element breakdown
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near engine block)
• Chafed wires along the harness routing path between sensor and ECM, particularly where harness contacts frame rails
• Corroded or loose ground connections affecting sensor circuit integrity
• Contaminated coolant causing sensor element coating or failure
• ECM internal circuit fault (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code E112

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block's coolant passage. Check the connector for corrosion, moisture, or damaged pins. On used excavators, examine the entire wiring harness for rub-through points, especially where it routes near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). Test harness continuity from sensor connector to ECM pins, checking for opens or shorts to ground.

Step 3: Voltage Signal Check With ignition on and sensor connected, backprobe the signal wire at the connector. You should read approximately 5 volts with sensor disconnected, dropping to 2-3 volts when connected and engine cold. Abnormal readings indicate harness or ECM issues.

Step 4: Component Replacement If sensor resistance is out of specification or harness testing reveals damage, replace the faulty component. For used machines, always apply dielectric grease to connectors and secure harnesses away from heat sources and moving parts to prevent recurrence.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic equipment.