What is Caterpillar Fault Code SPN673?

SPN673 indicates a problem with the Engine Coolant Level sensor circuit or an actual low coolant condition in Caterpillar engines and equipment. This Suspect Parameter Number (SPN) monitors the coolant level sensor's electrical circuit and the physical coolant level in the expansion tank or radiator. When triggered, the Electronic Control Module (ECM) detects either an open/short circuit in the sensor wiring or critically low coolant levels that could lead to engine overheating.

This code is critical for Caterpillar excavators because inadequate coolant levels can cause catastrophic engine damage, including warped cylinder heads, blown head gaskets, or complete engine seizure. In used machines, this fault often indicates aging cooling system components or electrical deterioration that demands immediate attention to prevent expensive repairs.

Common Symptoms

• Coolant warning light illuminated on the instrument cluster or display panel
• Engine derate mode activated, limiting machine power output to prevent overheating
• Audible warning alarm sounding in the operator cab
• Visible coolant leaks around hoses, radiator, or water pump assemblies
• Engine running hotter than normal operating temperature (190-205°F range)

Potential Causes

The most common technical reasons for SPN673 in used Caterpillar excavators include:

• Damaged or corroded wiring harness connections at the coolant level sensor, particularly at harness rub points near the radiator mounting brackets
• Failed coolant level sensor due to internal corrosion or contaminated coolant degrading sensor contacts
• Actual low coolant level from external leaks (deteriorated hoses, radiator seams, water pump seals)
• ECM internal fault misreading sensor signals (rare but possible in high-hour machines)
• Corroded or loose ground connections affecting sensor circuit integrity
• Damaged expansion tank or radiator cap allowing coolant loss through evaporation

How to Troubleshoot and Fix Code SPN673

Step 1: Visual Inspection Check the physical coolant level in the expansion tank with the engine cold. Inspect for visible leaks around hoses, clamps, radiator, and water pump. Examine the coolant level sensor connector for corrosion, pushed-back pins, or moisture intrusion—common in used excavators operating in harsh environments.

Step 2: Electrical Testing Using a digital multimeter, disconnect the coolant level sensor and measure resistance across the sensor terminals. Compare readings against Caterpillar specifications (typically 100-300 ohms when submerged). Check for open circuits or shorts to ground in the wiring harness between the sensor and ECM using continuity testing.

Step 3: Sensor and Harness Evaluation Inspect the sensor harness for wear at known rub points near frame rails and engine mounts. On used machines, wiring insulation often deteriorates from heat cycling and vibration. Test supply voltage at the sensor connector (should read approximately 5V reference voltage from ECM). Replace sensor if electrical values are out of specification.

Step 4: System Verification After repairs, refill coolant to proper levels using manufacturer-specified coolant mixture. Clear codes using Caterpillar Electronic Technician (Cat ET) diagnostic software and perform a functional test under operating temperature.

Disclaimer: This guide provides general troubleshooting information. Always consult Caterpillar service manuals and consider professional diagnostic services for complex electrical issues or major repairs on used equipment.