Komatsu PC200‑8 Error Code E15: Complete Coolant Temperature Sensor Diagnosis & Fix

 

 Decoding Komatsu Error Code E15: Why It’s More Than Just a Bad Sensor

You're halfway through a trenching job when the alarm sounds. A quick look at the monitor confirms it—Error Code E15. Suddenly, your Komatsu PC200‑8 loses power, feels sluggish, and refuses to work at full capacity.

This isn’t just an inconvenience. It’s the machine’s MCU (Machine Control Unit) entering protective mode because it no longer trusts the coolant temperature data it’s receiving.

Before you call in a service truck, understand this: E15 doesn’t always mean a major failure. It simply means the coolant temperature sensor circuit is sending an impossible signal. With a logical diagnostic approach, you can pinpoint the real cause and fix it efficiently.

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Understanding Error Code E15: More Than a Simple Glitch

On the Komatsu PC200‑8, Error Code E15 translates to:

✅ Engine Coolant Temperature Sensor Circuit Problem

This code appears when the MCU receives a voltage signal from the coolant temperature sensor that is outside the valid range.
It’s not saying “the engine is overheating”—it’s saying:

“The temperature reading makes no sense.”

The MCU depends on accurate coolant temperature data for:

• Fuel Injection Timing – ensures efficient combustion
• Cooling Fan Control – adjusts hydraulic fan speed
• Engine Derating – protects the engine when overheating is suspected

When the signal is invalid, the MCU assumes the worst and reduces engine power to prevent damage. Ignoring E15 forces the machine into an inefficient limp mode, wasting fuel and productivity.

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How the Coolant Temperature Sensor Actually Works

To diagnose E15 correctly, you need to understand how the sensor communicates.

Inside the sensor is an NTC thermistor (Negative Temperature Coefficient). Its resistance drops as temperature rises.

How the signal is created:

1. The MCU sends a stable 5V reference to the sensor.
2. The sensor acts as a variable resistor to ground.
3. Cold engine → high resistance → high return voltage (e.g., 4.5V)
4. Hot engine → low resistance → low return voltage (e.g., 0.5V)
5. The MCU converts this voltage into a temperature reading.

E15 is triggered when:

• The return voltage is too high → open circuit / impossible cold
• The return voltage is too low → short circuit / impossible hot

Your job is to find out why the voltage is wrong.

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Step-by-Step Diagnostic Guide for Komatsu E15

Before starting, ensure the machine is on level ground, the implement is lowered, and the engine is cool.

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Step 1: Visual Inspection — The Most Overlooked Fix

Follow the wiring from the coolant temperature sensor (usually near the thermostat housing). Look for:

• Chafed or melted wires
• Loose, oily, or corroded connectors
• Rodent damage
• Harness pinched against brackets

A disconnected or damaged wire is one of the most common causes.

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Step 2: Test the Coolant Temperature Sensor

1. Disconnect the sensor connector.   
    
   
2. Set your multimeter to Ohms (Ω).
3. Measure resistance across the sensor terminals.
4. At ~20°C, expect 2,000–3,000 Ω (check manual for exact spec).
5. Warm the engine, shut it off, and measure again.
6. At operating temperature, expect 200–500 Ω.

Sensor verdict:

• Infinite resistance → open circuit → bad sensor
• Zero resistance → shorted sensor → bad sensor
• Values far from spec → replace sensor
• Logical change with temperature → sensor is good

If the sensor passes, move on to the wiring.

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Step 3: Check the Wiring Harness for Opens or Shorts

You’ll need the wiring diagram to identify the correct MCU pin.

Test for open circuit:

• Meter on continuity
• One probe on sensor signal wire
• Other probe on MCU signal pin
• Low resistance (<1 Ω) = good
• OL / infinite = wire break

Test for short to ground:

• One probe on sensor signal wire
• Other probe on engine ground
• No continuity = good
• Beep / continuity = wire shorted to ground

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Step 4: Check the Reference Voltage (Rare but Possible)

1. Reconnect the sensor.
2. Key ON, engine OFF.
3. Back-probe the signal wire.
4. You should see 5V reference.

If you see 0V, the issue may be in the MCU power supply or reference circuit.

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Fixing the Problem: What to Do After Diagnosis

✅ Faulty Sensor

Replace with OEM or high-quality equivalent. Use proper thread sealant.

✅ Damaged Wiring

Repair using solder + heat-shrink tubing. Avoid electrical tape.

✅ Bad Connector

Clean with electrical contact cleaner and ensure proper locking.

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Final Step: Clear the Error Code

After repairs, the MCU must be reset.
On the PC200‑8, this is typically done via:

• The monitor panel service menu → Clear Active Faults
• Or disconnecting the battery for several minutes

If you don’t clear the code, the machine may stay in derate mode.

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Pro Tip: Why This Small Sensor Matters More Than You Think

A drifting or inaccurate coolant temperature sensor can cause:

• Rich fuel mixture → high fuel consumption, black smoke
• Poor performance → incorrect timing
• Unnecessary fan operation → wasted hydraulic power

FAQs for Komatsu PC200‑8 Error Code E15

1. What does Error Code E15 mean on a Komatsu PC200‑8?

Error Code E15 indicates a coolant temperature sensor circuit problem, usually caused by an open or shorted signal.

2. Does E15 mean my Komatsu excavator is overheating?

No. E15 means the temperature reading is invalid — not that the engine is actually overheating.

3. What symptoms appear when E15 is active?

You may experience power loss, sluggish operation, derate mode, and incorrect fan speed.

4. Where is the coolant temperature sensor located on the PC200‑8?

It is typically mounted near the thermostat housing on the engine block.

5. Can a bad coolant temperature sensor cause engine derating?

Yes. When the MCU receives an impossible temperature signal, it reduces engine power to protect the engine.

6. How do I test the coolant temperature sensor?

Use a multimeter to measure resistance. High resistance when cold and low resistance when hot indicates normal behavior.

7. What resistance values should the sensor show?

Around 2,000–3,000 Ω at 20°C and 200–500 Ω at operating temperature (varies by model).

8. Can wiring issues trigger the E15 fault code?

Absolutely. Broken wires, corrosion, loose connectors, or shorts to ground are common causes.

9. How do I clear Error Code E15 after fixing the issue?

Use the monitor service menu to clear active faults or disconnect the battery for several minutes.

10. Is it safe to keep operating the excavator with E15 active?

No. The machine runs in derate mode, reducing performance and increasing fuel consumption. Fixing the issue restores normal operation.