When dealing with modern diesel engines, diagnostic trouble codes like SPN 4374/FMI 0 – GHG14 can be critical indicators of underlying issues in the Diesel Exhaust Fluid (DEF) system. This code typically signifies that the DEF pump speed is higher than normal for a given DEF pressure. In this article, we’ll explore the causes, diagnostic steps, and solutions for resolving SPN 4374/FMI 0, ensuring your vehicle’s emissions system operates efficiently.
What Does SPN 4374/FMI 0 – GHG14 Mean?
SPN 4374/FMI 0 – GHG14 is a diagnostic code that indicates an issue with the DEF pump speed relative to the DEF pressure. This discrepancy can lead to various problems, including reduced engine performance and increased emissions. The code is monitored continuously when enabling conditions are met, and it typically results in a 25% engine derate, along with the illumination of the MIL (Malfunction Indicator Lamp) and CEL (Check Engine Light).
Possible Causes of SPN 4374/FMI 0
Several factors can trigger SPN 4374/FMI 0, including:
- Restrictions in the DEF lines between the DEF tank and the DEF pump or between the DEF pump and the DEF dosing unit.
- Air in the DEF lines, which can disrupt the fluid flow.
- Restrictions or failures in the DEF pump, leading to abnormal pump speeds.
- Contamination of DEF fluid with diesel fuel or oil, which can affect system performance.
Diagnostic Steps for SPN 4374/FMI 0
Step 1: Connect DiagnosticLink®
Begin by connecting DiagnosticLink® to the vehicle’s system to retrieve diagnostic information.
Step 2: Check for Multiple Codes
Turn the ignition ON (key ON, engine OFF) and check for additional codes such as SPN 4334/FMI 3, 4, SPN 4375/FMI 3, 4, or SPN 3361/FMI 3, 4, 5. If these codes are present, diagnose and repair them first.
Step 3: Compare DEF Pressure and Barometric Pressure
Compare the AS110: ADS DEF pressure 2 reading to the barometric pressure sensor reading. If the readings are within 5 psi of each other, proceed to the next step. If not, replace the DEF dosing unit.
Step 4: Check for DEF Contamination
Turn the ignition OFF and use a DEF test strip (A0005850202) to check for diesel fuel or oil contamination. If contamination is found, replace the DEF tank, header, supply line, return line, pump, and dosing unit, then refill with new DEF.
Step 5: Inspect DEF Lines
Inspect the DEF lines for damage, pinches, or kinks. Replace any damaged lines.
Step 6: Perform SCR ADS Self-Check
Disconnect the DEF supply line at the dosing unit and perform the Selective Catalyst Reduction Airless Dosing System (SCR ADS) self-check routine. Check for continuous air bubbles indicating a crack in the DEF pump feed line. If bubbles are present, replace the DEF supply line.
Step 7: Replace DEF Pump Components
Replace the DEF pump module filter, inlet screen, and pressure relief valve. Also, replace the DEF dosing unit inlet screen.
Step 8: Verify Repairs
Reconnect all DEF lines and electrical connections, then perform the SCR ADS self-check routine again. If the test passes, clear the codes and release the vehicle. If not, replace the DEF pump.
Conclusion
Resolving SPN 4374/FMI 0 – GHG14 requires a systematic approach to diagnose and repair issues within the DEF system. By following the steps outlined above, you can ensure your vehicle’s emissions system operates efficiently, maintaining compliance with environmental regulations and optimal engine performance. Regular maintenance and timely repairs are essential to prevent recurring issues and keep your vehicle running smoothly.
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