SPN 2659 FMI 18 – EGR Flow Target Error Diagnostic - Low Flow Fault Code (Symptoms, Causes & Fix)
The SPN 2659 FMI 18 fault code is a diesel engine fault code indicating an EGR Flow Target Error due to low flow. This diagnostic trouble code is triggered when the Engine Control Module (ECM) detects that the actual EGR flow is significantly lower than the target flow. This discrepancy suggests a problem within the EGR system, which is crucial for reducing NOx emissions by recirculating a portion of the exhaust gases back into the engine cylinders.
What SPN 2659 FMI 18 Means
The SPN 2659 FMI 18 fault code specifically points to an issue with the Exhaust Gas Recirculation (EGR) system, where the ECM identifies a lower-than-expected flow of exhaust gases. This could be due to mechanical blockages, sensor failures, or issues with the EGR valve operation. The ECM uses inputs from various sensors to monitor and control the EGR flow, and any deviation from expected values results in this fault code.
Common Causes of This Fault Code
- EGR valve stuck closed or partially closed
- EGR differential pressure sensor failure
- Clogged EGR cooler or passages
- Wiring harness issues related to EGR valve or sensors
- Faulty EGR actuator
Symptoms Drivers May Notice
When the SPN 2659 FMI 18 fault code is active, drivers may notice a reduction in engine performance, increased exhaust emissions, or the Check Engine Light illuminating. In some cases, the engine may enter a derate mode to prevent damage, leading to reduced power output.
How Technicians Diagnose This Fault
Technicians begin diagnosing this fault with a visual inspection of the EGR system, checking for carbon buildup or blockages in the EGR valve and cooler. Next, they use a scan tool to command the EGR valve open and closed, verifying its operation. The EGR differential pressure sensor readings are measured using a multimeter or scan tool to ensure they are within specification. Wiring harnesses and connectors are inspected for damage or corrosion, which could affect sensor signals. A smoke test may be performed to check for leaks in the EGR system.
Common Misdiagnosis
Technicians often misdiagnose this fault by replacing the EGR valve without checking for carbon buildup, assuming a sensor failure without verifying wiring integrity, or overlooking clogged EGR cooler or passages. Proper testing and inspection are crucial to avoid unnecessary part replacements.
Can You Keep Driving?
While it may be possible to continue driving with the SPN 2659 FMI 18 fault code active, it is not advisable. The fault can lead to increased emissions and potential engine derate, which reduces power and efficiency. Addressing the issue promptly is recommended to avoid further complications.
Mechanic's Diagnostic Tip
When diagnosing SPN 2659 FMI 18, always verify the EGR valve's operation with a scan tool before considering replacement. Often, cleaning carbon deposits from the valve and cooler can resolve the issue without the need for new parts.
Frequently Asked Questions
- What does SPN 2659 FMI 18 indicate? It indicates an EGR Flow Target Error due to low flow, suggesting issues within the EGR system.
- Can a faulty EGR valve cause this code? Yes, a stuck or malfunctioning EGR valve is a common cause of this fault code.
- Is it safe to drive with this fault code? While you can drive, it's not recommended due to potential engine derate and increased emissions.
