What is Hitachi EX200-3 Fault Code 157-2?

Hitachi EX200-3 Fault Code 157-2 indicates an abnormal signal from the engine oil pressure sensor circuit, specifically a low voltage condition detected by the Engine Control Module (ECM). This code triggers when the ECM receives a voltage reading below the acceptable threshold from the oil pressure sensor, suggesting either insufficient oil pressure, sensor malfunction, or electrical circuit problems.

This fault is critical for the EX200-3's Isuzu 6BG1 engine because proper oil pressure monitoring prevents catastrophic engine damage. The ECM relies on accurate oil pressure data to protect internal engine components from inadequate lubrication. When this code activates, the machine may enter derate mode or initiate shutdown protocols to prevent engine seizure or bearing failure.

Common Symptoms

• Oil pressure warning light illuminated continuously on the instrument panel
• Engine derate with reduced power output or inability to reach full RPM
• Audible alarm sounding from the cab, indicating critical pressure issue
• Engine shutdown after a brief warning period if pressure remains critically low
• Intermittent stalling or rough idle, particularly when the engine is warm

Potential Causes

The most common causes of Code 157-2 on used EX200-3 excavators include:

• Failed oil pressure sensor due to internal diaphragm deterioration or contamination from metal particles in aged oil
• Damaged wiring harness near the sensor mounting point where vibration causes wire chafing against the engine block
• Corroded connector terminals at the sensor plug, especially common in machines operating in humid or marine environments
• Low engine oil level or use of incorrect viscosity oil causing actual pressure drop
• ECM ground circuit issues creating voltage reference problems
• Worn oil pump in high-hour machines reducing actual oil pressure below safe thresholds

How to Troubleshoot and Fix Code 157-2

Step 1: Visual Inspection Check actual engine oil level using the dipstick and inspect oil condition. Examine the oil pressure sensor (located on the left side of the engine block) for oil leaks, physical damage, or loose mounting. Inspect the wiring harness from sensor to ECM for abraded insulation, particularly where it routes near the engine mount bracket—a known wear point on the EX200-3.

Step 2: Electrical Testing Disconnect the sensor connector and inspect terminals for corrosion or bent pins. Using a digital multimeter, measure resistance across the sensor terminals (typical specification: 50-150 ohms at room temperature). Check voltage supply at the connector with ignition on—should read approximately 5 volts from the ECM. Verify ground circuit continuity with resistance below 1 ohm.

Step 3: Sensor and System Verification If electrical tests pass, install a mechanical oil pressure gauge temporarily to verify actual oil pressure (should be 30-50 PSI at idle, 50-70 PSI at high idle). For used excavators, remove and inspect the sensor port for sludge buildup that can restrict oil flow to the sensor. Replace the oil pressure sensor if mechanical pressure is adequate but electrical signal remains faulty. Clear codes using Hitachi diagnostic software (Dr.EX) or compatible scan tool and test operate.

Disclaimer: This guide provides general troubleshooting information. Always consult the Hitachi EX200-3 service manual and consider professional diagnosis for complex electrical issues or if unfamiliar with high-pressure hydraulic systems.