Komatsu PC750LC-7 Fault Code E117: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code E117?

Fault Code E117 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low engine oil pressure detected by the Engine Control Module (ECM). This code specifically relates to the oil pressure monitoring system that protects the Komatsu SAA6D140E-5 engine from catastrophic damage due to inadequate lubrication.

The oil pressure sensor sends continuous voltage signals to the ECM, which monitors whether oil pressure remains within the manufacturer's specified range during operation. When the ECM detects voltage readings outside normal parameters (typically 0.5-4.5V) or actual pressure below critical thresholds, it triggers E117 and initiates protective measures. For the PC750LC-7, maintaining proper oil pressure is absolutely critical—this 750-class excavator's engine operates under extreme loads, and insufficient lubrication can destroy bearings, camshafts, and crankshafts within minutes.

Common Symptoms

• Engine derate or automatic shutdown after the code activates, preventing operation until the issue is resolved
• Red oil pressure warning light illuminated on the monitor panel, often accompanied by audible alarms
• Rough engine idle or unusual mechanical noise (knocking or ticking) if actual oil pressure is genuinely low
• Monitor display showing abnormal oil pressure readings (either zero, extremely low, or erratic fluctuations)
• Intermittent code appearance during cold starts or after extended idle periods on used machines

Potential Causes

• Faulty oil pressure sensor (common failure point on high-hour machines, typically located on the engine block's left side)
• Damaged or corroded wiring harness between the sensor and ECM, especially at connector pins or where harness rubs against frame components
• Low engine oil level or use of incorrect viscosity oil for operating conditions
• Worn oil pump or clogged oil pickup screen reducing actual pressure (common in used excavators with 8,000+ hours)
• Defective ECM or internal ECM software corruption (rare but possible on older units)
• Blocked oil passages or sludge buildup in the lubrication system from poor maintenance history

How to Troubleshoot and Fix Code E117

Step 1: Verify Actual Oil Condition and Level Before electrical diagnostics, check the dipstick to confirm proper oil level and inspect oil quality. On used excavators, contaminated or severely degraded oil can cause genuine pressure problems. Look for metal particles, excessive sludge, or fuel dilution.

Step 2: Inspect Oil Pressure Sensor and Connections Locate the oil pressure sensor on the engine block (consult service manual for exact location). Disconnect the sensor connector and inspect for corrosion, bent pins, or oil contamination inside the connector—extremely common on machines operating in wet or dusty environments. Clean connections with electrical contact cleaner.

Step 3: Test Sensor Resistance and Voltage Using a digital multimeter, measure sensor resistance (typically 50-450 ohms depending on temperature). With ignition on and sensor connected, backprobe the signal wire to verify voltage output (should read 0.5-4.5V). Compare readings against Komatsu specifications in the service manual.

Step 4: Check Wiring Harness Continuity Trace the sensor harness from sensor to ECM, checking for damaged insulation, especially where it passes near hot exhaust components or sharp edges. Perform continuity tests on signal and ground wires. On used PC750LC-7s, harness wear near the engine mount area is a known issue.

Step 5: Verify Actual Oil Pressure with Mechanical Gauge Install a mechanical oil pressure gauge in place of the sensor to confirm actual pressure (should be 30-60 PSI at operating temperature). If mechanical pressure is adequate but the code persists, replace the sensor. If pressure is genuinely low, investigate oil pump wear or internal engine problems.

Step 6: Clear Code and Monitor After repairs, use Komatsu diagnostic software (KOMTRAX or PC-based tools) to clear the fault code. Operate the machine through various load conditions while monitoring oil pressure readings in real-time to confirm the fix.

---

Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu service manual for your specific machine serial number. If you lack proper diagnostic tools or experience with high-pressure hydraulic systems, consult a certified Komatsu technician to prevent injury or further equipment damage.