What is Komatsu PC200-7 Fault Code H-5?

Fault Code H-5 on the Komatsu PC200-7 indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature detected by the machine's monitoring system. This code is triggered when the hydraulic oil temperature exceeds approximately 110°C (230°F) or when the temperature sensor circuit experiences an electrical fault, such as an open circuit, short circuit, or voltage irregularity.

The hydraulic system is the lifeblood of the PC200-7 excavator, powering all boom, arm, bucket, and swing functions. The hydraulic oil temperature sensor communicates critical temperature data to the Electronic Control Module (ECM), which regulates pump output and protects components from thermal damage. When this sensor fails or detects overheating, the machine may enter a protective derate mode to prevent catastrophic damage to hydraulic pumps, seals, and valves. On used excavators, this code frequently appears due to sensor degradation, wiring harness damage from years of vibration, or actual cooling system failures that allow temperatures to climb unchecked.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument panel (typically red or amber)
• Reduced hydraulic response or sluggish movement of boom, arm, and swing functions as the system derates
• Intermittent alarm buzzer sounding in the operator cabin
• Machine automatically limiting engine RPM to reduce hydraulic pump speed and heat generation
• Visible steam or excessive heat radiating from the hydraulic tank or cooler assembly

Potential Causes

The most common technical causes of H-5 on used PC200-7 excavators include:

• Faulty hydraulic oil temperature sensor due to internal element failure or corrosion on terminals
• Damaged or chafed wiring harness near the hydraulic tank, particularly where harnesses contact the tank mounting bracket or frame
• Clogged hydraulic oil cooler restricting airflow and preventing adequate heat dissipation
• Low hydraulic oil level causing insufficient cooling capacity and elevated operating temperatures
• Failed cooling fan motor or damaged fan blades reducing airflow through the hydraulic cooler
• Deteriorated hydraulic oil with breakdown of additives, increasing friction and heat generation
• Malfunctioning ECM providing incorrect temperature readings or triggering false alarms

How to Troubleshoot and Fix Code H-5

Step 1: Verify Actual Hydraulic Oil Temperature Before assuming sensor failure, use an infrared temperature gun to measure the actual temperature at the hydraulic tank surface. Compare this reading to the display temperature on the monitor panel. If the physical temperature is below 100°C but the code persists, the issue is likely sensor or wiring-related rather than actual overheating.

Step 2: Inspect the Temperature Sensor and Connector Locate the hydraulic oil temperature sensor mounted on the hydraulic tank (typically on the left side near the return filter). Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture intrusion—common issues on used excavators operating in harsh environments. Clean connector terminals with electrical contact cleaner and ensure the rubber seal is intact.

Step 3: Test Sensor Resistance Using a digital multimeter, measure the resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult the PC200-7 service manual for exact specifications). If readings are infinite (open circuit) or near zero (short circuit), the sensor requires replacement (Komatsu part number 7861-93-3320 or equivalent).

Step 4: Check Wiring Harness Continuity Trace the wiring harness from the sensor back to the ECM connector. On used PC200-7 machines, inspect known rub points where the harness passes over the hydraulic tank mounting bracket and along the right-side frame rail. Look for abrasion damage, exposed copper, or wire breakage. Test continuity with a multimeter—resistance should be less than 5 ohms from sensor connector to ECM pin. Repair or replace damaged sections using OEM-spec weather-resistant wire and protective loom.

Step 5: Inspect Hydraulic Cooling System Components If sensor testing confirms proper operation but high temperatures persist, address cooling system issues. Check hydraulic oil level at the sight glass (should be between MIN and MAX marks when cold). Inspect the hydraulic oil cooler for debris blockage, bent fins, or internal restriction—remove and pressure-wash if necessary. Verify the cooling fan motor operates when hydraulic temperature rises by observing fan engagement during a 15-minute work cycle under load.

Step 6: Clear Code and Monitor After repairs, use Komatsu diagnostic software (KOMTRAX or PC-based service tool) to clear stored fault codes. Operate the machine under normal working conditions for at least one hour, monitoring hydraulic oil temperature. If the code does not reappear and temperatures stabilize below 95°C, the repair is successful.

Disclaimer: This guide provides general troubleshooting procedures for informational purposes. Hydraulic systems operate under extreme pressure and temperature. Always consult the official Komatsu PC200-7 service manual and consider professional assistance from a certified heavy equipment technician for complex diagnostics and repairs. Improper repairs may result in equipment damage or personal injury.