Komatsu PC220-10 Fault Code CA351: Complete Diagnostic Guide

What is Komatsu PC220-10 Fault Code CA351?

Fault Code CA351 indicates a malfunction in the engine coolant temperature sensor circuit, specifically an abnormal voltage signal detected by the Engine Control Module (ECM). This code triggers when the ECM receives a voltage reading outside the expected range from the coolant temperature sensor, typically located on the engine block near the thermostat housing.

The coolant temperature sensor is critical for the PC220-10's performance management system. It directly influences fuel injection timing, engine warm-up cycles, and exhaust gas recirculation (EGR) operation. When this sensor fails or sends incorrect signals, the ECM cannot properly regulate engine temperature, potentially leading to reduced fuel efficiency, increased emissions, and inadequate engine protection during cold starts or overheating conditions.

Common Symptoms

When CA351 is active on your Komatsu PC220-10, operators typically experience:

• Check Engine Light illuminated on the instrument cluster with reduced engine power output
• Extended warm-up periods or difficulty reaching optimal operating temperature
• Rough idle during cold starts, with black smoke from the exhaust
• Engine derate mode activation, limiting maximum RPM to approximately 1,800-2,000 range
• Erratic temperature gauge readings or gauge stuck at cold/hot positions regardless of actual engine temperature

Potential Causes

The most common technical causes for CA351 on used PC220-10 excavators include:

• Coolant temperature sensor failure due to age-related internal resistance drift (common after 5,000-8,000 operating hours)
• Damaged wiring harness at known rub points near the engine mount bracket and fuel filter assembly
• Corroded or moisture-contaminated connectors on the sensor plug, especially on machines operated in wet or coastal environments
• Intermittent open or short circuits in the signal wire between the sensor and ECM
• ECM internal circuit fault (less common, but possible on high-hour machines with previous electrical issues)
• Incorrect sensor installation after previous repairs, causing poor thermal contact with coolant jacket

How to Troubleshoot and Fix Code CA351

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block's coolant outlet. Inspect the wiring harness from sensor to ECM for obvious damage, chafing, or corrosion. On used excavators, pay special attention to harness routing near the engine mounts—vibration over time commonly wears through insulation here.

Step 2: Electrical Testing Disconnect the sensor connector and measure resistance across the sensor terminals using a digital multimeter. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. Compare your reading against Komatsu specifications in the service manual. Check for voltage supply at the harness connector—you should see approximately 5 volts reference voltage from the ECM with the ignition on.

Step 3: Signal Wire Continuity Test continuity and resistance of the signal wire from the sensor connector back to the ECM pin C-22 (consult wiring diagrams for your specific serial number). Resistance should be less than 5 ohms. Check for shorts to ground or power by measuring resistance between the signal wire and chassis ground—it should read infinite resistance.

Step 4: Connector and Ground Inspection Clean all connector terminals with electrical contact cleaner. Inspect for bent pins or green corrosion—common on machines with 3,000+ hours. Verify the engine ground straps are tight and corrosion-free, as poor grounding causes voltage irregularities that trigger CA351.

Step 5: Component Replacement If sensor readings are out of specification, replace the coolant temperature sensor with a genuine Komatsu part (part number 6261-81-6310 or equivalent for your engine serial number). Use new Viton O-rings and apply anti-seize compound to threads. After replacement, clear codes using Komatsu diagnostic software (KDPF) and perform a test run to verify repair.

Disclaimer: This guide provides general diagnostic procedures for informational purposes. Always consult the official Komatsu PC220-10 service manual and qualified diesel technicians for definitive diagnostics. Improper repairs may cause engine damage or void remaining warranties on used equipment.