What is Komatsu PC300-7 Fault Code E112?

Fault Code E112 on the Komatsu PC300-7 indicates a malfunction in the engine coolant temperature sensor circuit. This code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically reading values outside the expected range of 0.5 to 4.5 volts. The coolant temperature sensor plays a critical role in engine management by providing real-time temperature data to the ECM, which adjusts fuel injection timing, idle speed, and cooling fan operation accordingly. On used PC300-7 excavators, this fault can lead to inefficient combustion, increased fuel consumption, and potential engine overheating if left unaddressed.

Common Symptoms

When Code E112 is active on your Komatsu PC300-7, you may experience:

• Engine warning light illuminated on the instrument panel, often accompanied by an audible alarm
• Hard starting or extended cranking time, especially during cold starts
• Erratic idle speed or hunting (RPM fluctuation) when the machine is at operating temperature
• Cooling fan running continuously at high speed, even when the engine is cold
• Reduced engine performance or entering a derate mode to protect components from thermal damage

Potential Causes

The most common technical causes for Code E112 on used PC300-7 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged wiring harness at known rub points near the engine block mounting brackets or behind the alternator
• Corroded or loose electrical connectors at the sensor terminal—especially prevalent in machines operated in humid or coastal environments
• Open or short circuit in the sensor signal wire between the sensor and ECM connector
• ECM internal fault (rare, but possible in high-hour machines with electrical system issues)

How to Troubleshoot and Fix Code E112

Step 1: Visual Inspection
Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, moisture intrusion, or bent pins. On used excavators, check the wiring harness for abrasion points where it contacts metal surfaces—this is a common failure point on PC300-7 models.

Step 2: Electrical Testing
Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms; at 176°F (80°C), it should drop to around 200-400 ohms. Compare your readings to Komatsu specifications. Also check for continuity between the sensor connector and ECM pin 23 (signal wire).

Step 3: Signal Voltage Check
With the sensor connected and ignition on (engine off), backprobe the sensor connector and measure voltage at the signal wire. You should see approximately 5 volts from the ECM reference supply. If voltage is absent or incorrect, trace the harness for breaks or check ECM power supply circuits.

Step 4: Component Replacement
If sensor resistance values are out of specification or the connector shows significant corrosion, replace the coolant temperature sensor with a genuine Komatsu part (part number 6732-81-3140). After replacement, clear the fault code using Komatsu diagnostic software (VCADS or equivalent) and monitor for recurrence during a full heat cycle.

Disclaimer: This guide provides general diagnostic procedures. For complex electrical issues or if you're unfamiliar with excavator systems, consult a certified Komatsu technician or authorized service center. Always disconnect the battery before performing electrical repairs.