SPN 175 FMI 15 – Oil Temperature High Pre-Warning Fault Code (Symptoms, Causes & Fix)

Mar 22, 2026

The SPN 175 FMI 15 fault code is a diesel engine diagnostic trouble code indicating an oil temperature high pre-warning condition. This code is triggered when the Engine Control Module (ECM) detects that the oil temperature is approaching a critical level, potentially leading to engine damage if not addressed. Understanding this fault code is crucial for maintaining engine health and preventing costly repairs.

What SPN 175 FMI 15 Means

The SPN 175 FMI 15 fault code specifically relates to the engine's lubrication system, where the ECM monitors the oil temperature through a sensor. When the oil temperature rises above a predefined threshold, the ECM logs this fault to alert the operator of a potential overheating issue. This pre-warning allows for corrective action before the oil temperature reaches a level that could cause engine damage.

Common Causes of This Fault Code

Low engine oil level
Faulty oil temperature sensor
Restricted oil cooler
Oil pump malfunction
Excessive engine load or overheating

Symptoms Drivers May Notice

When the SPN 175 FMI 15 fault code is active, drivers may notice the engine warning light illuminated on the dashboard. Additionally, there might be a noticeable increase in engine temperature readings, and in severe cases, the engine may enter a derate mode to prevent damage.

How Technicians Diagnose This Fault

Diagnosing the SPN 175 FMI 15 fault code involves a systematic approach:

Begin with a visual inspection of the engine oil level and quality. Ensure the oil is at the correct level and not contaminated.
Inspect the oil temperature sensor and its wiring for any signs of damage or corrosion. Use a multimeter to verify the sensor's resistance and compare it to the manufacturer's specifications.
Check the oil cooler for any blockages or damage that might restrict oil flow.
Perform a pressure test on the oil pump to ensure it is functioning correctly and providing adequate oil pressure.
Examine the cooling system for any issues that could contribute to engine overheating, such as a malfunctioning thermostat or radiator problems.

Common Misdiagnosis

Technicians often misdiagnose this fault by assuming a sensor failure without proper testing. It's also common to overlook low oil levels as a potential cause or ignore issues within the cooling system that might lead to overheating.

Can You Keep Driving?

While it may be possible to continue driving with the SPN 175 FMI 15 fault code active, it is not advisable. Ignoring this warning can lead to severe engine damage if the oil temperature continues to rise unchecked. It's best to address the issue promptly to avoid engine derate or protection mode activation.

Mechanic's Diagnostic Tip

Always verify the oil temperature sensor's operation with a multimeter before considering replacement. Many unnecessary sensor replacements occur due to assumptions rather than testing. Ensure the sensor's resistance aligns with the manufacturer's specifications under various temperature conditions.

Frequently Asked Questions

What should I do if I see the SPN 175 FMI 15 code? Check the engine oil level and quality first, then proceed with further diagnostics as outlined.
Can a faulty oil temperature sensor cause this code? Yes, a malfunctioning sensor can trigger this code, but always test the sensor before replacing it.
Is it safe to drive with this fault code? It's best to address the issue immediately to prevent potential engine damage from overheating.