What is Komatsu PC220-10 Fault Code CA559?

Fault Code CA559 on the Komatsu PC220-10 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically an abnormally high voltage reading from the water temperature sensor (sensor 2) in the cooling system. This diagnostic trouble code (DTC) is generated when the Engine Control Module (ECM) detects a voltage signal above the normal operating range, typically indicating an open circuit, damaged wiring harness, or failed sensor.

The PC220-10's SAA6D107E-1 engine relies on precise coolant temperature data to optimize fuel injection timing, regulate diesel exhaust fluid (DEF) dosing, and control fan speed. When CA559 triggers, the ECM may default to failsafe values, potentially causing the engine to run inefficiently or enter derate mode. For used excavators, this code often signals age-related electrical degradation rather than actual overheating.

Common Symptoms

• Yellow or amber warning light illuminated on the instrument cluster with reduced engine power
• Engine running in derate mode (limited to 1,800 RPM or lower to protect components)
• Cooling fan running continuously at maximum speed, regardless of actual engine temperature
• Inaccurate coolant temperature readings on the monitor display (showing extremely high or implausible values)
• Difficulty starting in cold weather conditions due to improper cold-start fuel enrichment

Potential Causes

The most common technical reasons for CA559 on used PC220-10 machines include:

• Open circuit in the wiring harness between the ECM and the secondary coolant temperature sensor, often caused by wire chafing near the engine firewall or valve cover
• Failed water temperature sensor (sensor 2), typically located on the thermostat housing or cylinder head (part susceptible to corrosion in machines with 5,000+ operating hours)
• Corroded or loose connector pins at the sensor plug due to coolant seepage or moisture intrusion
• Damaged ECM input circuit caused by voltage spikes or previous electrical modifications
• Intermittent short-to-power in the harness from improper routing after previous repairs on used equipment

How to Troubleshoot and Fix Code CA559

Step 1: Verify the Fault with Diagnostic Software Connect Komatsu KTEC diagnostic software or a compatible scan tool to retrieve active and stored codes. Note freeze frame data showing voltage readings when CA559 was logged (values typically above 4.8V indicate open circuit).

Step 2: Inspect the Sensor and Connector Locate the secondary coolant temperature sensor (usually mounted near the thermostat housing on the right side of the engine). Disconnect the two-pin connector and thoroughly inspect for:

• Green corrosion on terminals (common in used excavators with coolant leaks)
• Bent or pushed-back pins preventing proper contact
• Coolant residue indicating a leaking sensor seal

Clean connectors with electrical contact cleaner and apply dielectric grease before reconnection.

Step 3: Test Sensor Resistance Using a digital multimeter, measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,300-2,700 ohms. An infinite (OL) reading confirms sensor failure. For used machines, also submerge the sensor in heated water and verify resistance decreases proportionally with temperature increase.

Step 4: Check Wiring Harness Continuity With the sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts on the signal wire (reference voltage from ECM). If voltage reads at battery level (12-24V), a short-to-power exists in the harness. Inspect wiring along the engine valley and behind the injection pump where harnesses commonly rub against brackets on older machines.

Step 5: Perform Harness Repair or Sensor Replacement Replace damaged sections of the engine harness using OEM-spec wire and heat-shrink connectors with sealant. On used excavators, thoroughly secure repaired harnesses away from heat sources and moving components. If sensor testing confirms failure, install a genuine Komatsu coolant temperature sensor (avoid aftermarket sensors that may have incorrect resistance curves causing false codes).

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu PC220-10 service manual and follow proper safety procedures. For complex electrical diagnostics or if fault codes persist after repairs, seek assistance from a certified Komatsu dealer or qualified heavy equipment technician.