Komatsu PC35MR-2 Fault Code S-2: Complete Diagnostic Guide

What is Komatsu PC35MR-2 Fault Code S-2?

Fault Code S-2 on the Komatsu PC35MR-2 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low engine oil pressure detection. This code is triggered when the Electronic Control Module (ECM) receives either an out-of-range signal from the oil pressure sensor or detects that actual oil pressure has fallen below the manufacturer's specified threshold during engine operation.

This fault is critical for the PC35MR-2's Yanmar 3TNV88-BKMST diesel engine because inadequate lubrication can cause catastrophic damage to bearings, pistons, and the crankshaft. The ECM monitors oil pressure continuously to protect internal engine components, making this code a high-priority alert that should never be ignored on used equipment.

Common Symptoms

• Engine Warning Lamp illuminated on the instrument panel, often accompanied by an audible alarm
• Engine derate mode or automatic shutdown to prevent internal damage (protection mode activation)
• Intermittent or constant low oil pressure gauge readings, even immediately after cold start
• Erratic oil pressure gauge behavior, fluctuating between normal and low readings during operation
• Reduced hydraulic performance or hesitation during boom/arm operations due to engine power limitation

Potential Causes

The S-2 code commonly appears due to several specific issues frequently found in used PC35MR-2 excavators:

• Failed oil pressure sensor (common wear item after 3,000+ hours)
• Damaged or corroded wiring harness connections at the sensor, particularly where the harness routes near the engine block heat source
• Actual low engine oil pressure caused by worn oil pump, clogged oil filter, or low oil level
• ECM ground connection issues creating false sensor readings
• Internal sensor contamination from degraded engine oil or metallic debris
• Harness chafing at known rub points near the engine mount brackets (common on older units)

How to Troubleshoot and Fix Code S-2

Step 1: Visual Inspection and Oil Level Verification Check engine oil level using the dipstick—ensure oil is at proper level and hasn't degraded. Inspect the oil pressure sensor (located on the right side of the engine block) for oil leaks, damaged connectors, or visible wire damage. On used excavators, carefully examine the wiring harness for friction wear where it contacts frame members.

Step 2: Electrical Testing with Multimeter Disconnect the oil pressure sensor connector. Using a digital multimeter, measure sensor resistance (typically 50-150 ohms at room temperature for this model). Check for supply voltage at the harness connector—should read approximately 5 volts with ignition on. Test ground circuit continuity between sensor ground pin and chassis ground (should be less than 1 ohm resistance).

Step 3: Dynamic Pressure Testing If electrical values are correct, install a mechanical oil pressure gauge into the sensor port. Start the engine and verify actual oil pressure meets Komatsu specifications (minimum 14 psi at idle, 43-57 psi at rated RPM). If mechanical pressure is adequate but code persists, replace the oil pressure sensor. If actual pressure is low, inspect the oil pump, pressure relief valve, and engine bearings.

Step 4: Advanced Diagnostics Use Komatsu diagnostic software (KOMTRAX or compatible scan tool) to monitor live sensor data and verify the ECM is receiving correct signals. Clear codes and perform a stationary regeneration test to confirm repair effectiveness.

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Professional Disclaimer: This guide provides general troubleshooting procedures for the Komatsu PC35MR-2. Engine oil pressure issues can indicate serious internal engine damage. If you're uncomfortable performing these diagnostics or if actual oil pressure is low, consult a certified Komatsu technician immediately to prevent catastrophic engine failure. Always refer to the official Komatsu service manual for complete specifications and torque values.