What is Komatsu PC120-6 Fault Code E233?

Fault Code E233 on the Komatsu PC120-6 indicates a malfunction in the hydraulic oil temperature sensor circuit. This code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the oil temperature sensor, typically reading values outside the normal operating range of 0.5-4.5 volts.

The hydraulic oil temperature sensor is critical for the PC120-6's performance management system. It monitors hydraulic fluid temperature and sends real-time data to the ECM, which adjusts pump output and engine speed to prevent overheating damage. When this sensor circuit fails, the machine cannot properly regulate hydraulic system temperature, potentially leading to accelerated component wear and reduced hydraulic efficiency.

Common Symptoms

• Warning lamp illuminates on the instrument panel, often accompanied by an audible alarm
• Hydraulic system operates in derate mode, limiting swing speed and digging force by approximately 20-30%
• Erratic temperature gauge readings or gauge stuck at minimum/maximum position
• Reduced overall machine performance, particularly during heavy excavation work
• ECM may log multiple instances of the code during operation cycles

Potential Causes

The most frequent causes of E233 on used PC120-6 excavators include:

• Sensor harness damage at known rub points near the hydraulic tank mounting bracket and main control valve
• Failed hydraulic oil temperature sensor due to prolonged exposure to heat cycles (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor plug (three-pin connector type)
• Internal ECM circuit degradation affecting the 5-volt reference supply
• Damaged wiring insulation from rodent activity in the engine compartment
• Contaminated hydraulic oil causing sensor element fouling

How to Troubleshoot and Fix Code E233

Step 1: Visual Inspection Locate the hydraulic oil temperature sensor on the left side of the hydraulic tank. Inspect the three-pin connector for corrosion, oil contamination, or bent pins. Check the wiring harness routing for chafing against metal edges, particularly where it passes near the tank bracket.

Step 2: Electrical Testing Disconnect the sensor connector. Using a multimeter, measure resistance across the sensor terminals. At 20°C (68°F), resistance should read approximately 2,000-3,000 ohms. Test the harness side for proper 5-volt reference from the ECM with ignition on. Check ground continuity (should be less than 1 ohm).

Step 3: Signal Testing With sensor connected and engine at operating temperature, backprobe the signal wire. Voltage should fluctuate between 0.5-4.5 volts as temperature changes. Static readings at 0V or 5V indicate open/short circuits.

Step 4: Component Replacement For used excavators, replace both the sensor and connector if corrosion exists. Use genuine Komatsu parts (P/N 7861-93-3320) to ensure proper calibration. Secure the harness with new clamps to prevent future abrasion.

Disclaimer: This guide provides general diagnostic information. Complex electrical issues should be diagnosed by certified Komatsu technicians with KomVision diagnostic software for accurate troubleshooting.