What is Caterpillar Fault Code 357?

Caterpillar Fault Code 357 indicates an Engine Oil Pressure Sensor Circuit Low Voltage condition. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects a voltage signal from the oil pressure sensor that falls below the manufacturer's specified threshold, typically below 0.5 volts.

This fault affects the engine's ability to accurately monitor oil pressure, which is critical for protecting internal components from catastrophic damage due to inadequate lubrication. The ECM relies on this sensor data to verify proper oil circulation throughout the engine's bearing surfaces, cylinder walls, and turbocharger. When Code 357 appears, the machine's protection systems may activate to prevent engine damage, potentially limiting performance or initiating shutdown protocols depending on the severity and your machine's programming.

Common Symptoms

• Oil pressure warning light illuminated on the instrument cluster or monitor display
• Engine derate mode activated, limiting machine power output to 50-75% of normal capacity
• Audible alarm or warning buzzer sounding continuously during operation
• Reduced hydraulic performance due to engine power limitations affecting pump output
• Engine shutdown in severe cases, particularly if the ECM interprets the signal as actual low oil pressure rather than a sensor circuit fault

Potential Causes

The most common technical causes for Code 357 on used Caterpillar excavators include:

• Damaged or corroded wiring harness between the oil pressure sensor and ECM, especially at known rub points near the engine block or frame rails
• Failed oil pressure sensor due to internal electrical failure or contamination from oil degradation
• Corroded connector pins at the sensor connection point, common in machines exposed to moisture or harsh environments
• Chafed wire insulation causing intermittent short-to-ground conditions in the sensor circuit
• ECM internal fault (less common) affecting the sensor input circuit
• Poor ground connection at the sensor mounting location due to corrosion or loose hardware

How to Troubleshoot and Fix Code 357

Step 1: Visual Inspection Begin by inspecting the oil pressure sensor and its wiring harness for obvious damage. Check the sensor connector for corrosion, bent pins, or moisture intrusion. On used excavators, pay special attention to harness routing where wires may contact hot engine surfaces or moving components. Clean all connector contacts with electrical contact cleaner and apply dielectric grease.

Step 2: Sensor Circuit Testing Using a digital multimeter (DMM), disconnect the oil pressure sensor and measure resistance across the sensor terminals. Typical resistance values range from 50-300 ohms depending on temperature, but consult your specific service manual. Next, check for circuit continuity from the sensor connector back to the ECM pins. Measure for less than 5 ohms resistance on signal wires and verify proper ground continuity.

Step 3: Voltage Signal Verification With the sensor reconnected and ignition on (engine off), backprobe the sensor connector and measure the supply voltage from the ECM, which should read approximately 5 volts. Start the engine and monitor the signal voltage, which should increase proportionally with oil pressure (typically 0.5-4.5 volts). If voltage remains below 0.5 volts with adequate oil pressure, replace the sensor.

Step 4: Advanced Diagnostics Connect Caterpillar Electronic Technician (Cat ET) diagnostic software to monitor real-time sensor data and compare readings against actual mechanical oil pressure gauge measurements. This identifies whether you have an electrical fault or actual low oil pressure. For used machines, consider testing oil pressure mechanically using a calibrated pressure gauge threaded into the sensor port to rule out actual lubrication system problems.

Disclaimer: This guide provides general diagnostic information. Always consult your machine's specific service manual and consider professional assistance from certified Caterpillar technicians for complex electrical diagnostics or if you're unsure about any procedure. Improper diagnosis may lead to incorrect repairs or engine damage.