Caterpillar Excavator Fault Code 6718: Technical Guide

What is Caterpillar Fault Code 6718?

Fault Code 6718 indicates an abnormal voltage condition detected in the Engine Oil Pressure Sensor circuit by the Electronic Control Module (ECM). This diagnostic trouble code (DTC) typically signals that the oil pressure sensor is sending voltage readings outside the expected range, preventing the ECM from accurately monitoring engine lubrication system performance.

In Caterpillar excavators, the oil pressure sensor is a critical component that monitors lubricant flow to engine bearings, camshafts, and turbocharger systems. When Code 6718 activates, the ECM cannot verify that adequate oil pressure exists, which may trigger protective engine derating or shutdown protocols. This is particularly critical in high-hour used machines where engine bearing clearances may already be compromised, making accurate oil pressure monitoring essential for preventing catastrophic engine damage.

Common Symptoms

When Code 6718 is active, operators typically experience:

• Check Engine light or malfunction indicator lamp (MIL) illuminated on the instrument cluster
• Engine derate mode activated, limiting machine to low idle or reduced RPM
• Oil pressure gauge reading zero, maximum, or fluctuating erratically regardless of actual engine condition
• Audible warning alarms in the cab, particularly on newer Caterpillar models with enhanced operator alert systems
• Automatic engine shutdown after a timed warning period if the ECM enters critical protection mode

Potential Causes

The most common technical causes for Code 6718 in used Caterpillar excavators include:

• Failed oil pressure sensor – internal sensor element degradation due to heat cycling and age
• Damaged sensor wiring harness – wire chafing at harness routing points near the engine block or frame rails (common wear location on high-hour machines)
• Corroded or contaminated electrical connectors – moisture intrusion at the sensor connector or ECM pins
• Open or short circuit in the sensor signal wire between the sensor and ECM
• ECM internal fault – rare, but possible in machines with electrical system history or previous water damage
• Incorrect sensor installation – cross-threaded or loose sensor causing intermittent electrical contact

How to Troubleshoot and Fix Code 6718

Step 1: Visual Inspection Begin with a thorough physical inspection of the oil pressure sensor (typically located on the engine block near the oil filter housing). Check for oil leaks around the sensor base, which indicate a failing seal that may allow moisture into the electrical connector. Inspect the wiring harness from the sensor to the ECM, paying special attention to areas where the harness contacts the frame, engine mounts, or passes through bulkheads—these are common friction points in used excavators.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the sensor and measure resistance across the sensor terminals. Consult your specific model's service manual for exact specifications, but most Caterpillar oil pressure sensors should read between 50-250 ohms at room temperature. Next, check for voltage supply at the harness connector with the key on, engine off—you should see approximately 5 volts reference voltage from the ECM. Test for continuity between the sensor connector and ECM pins to identify open circuits.

Step 3: Advanced Diagnostics Connect Caterpillar Electronic Technician (Cat ET) diagnostic software to verify real-time sensor voltage readings. Compare these values against the service manual's voltage-to-pressure conversion chart. If voltage readings are stuck at 0V or 5V regardless of engine operation, this confirms a circuit fault rather than an actual oil pressure problem. For used excavators, remove and inspect connector pins for corrosion or bent terminals—clean with electrical contact cleaner and dielectric grease.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Caterpillar oil pressure sensor (aftermarket sensors often have calibration variances that trigger repeat codes). After installation, torque to specification (typically 15-20 ft-lbs) and apply thread sealant as specified. Clear codes using diagnostic software and perform a stationary regeneration test to verify proper sensor operation across all RPM ranges.

---

Disclaimer: This guide provides general troubleshooting information. Always consult your machine's specific service manual and consider professional diagnosis by a certified Caterpillar technician, especially for used equipment with unknown maintenance history.