Understanding SPN 4357/FMI 5 – GHG14 Diagnostic Code: A Comprehensive Guide
When dealing with diesel exhaust fluid (DEF) systems, encountering diagnostic codes like SPN 4357/FMI 5 – GHG14 can be challenging. This code typically indicates an open circuit in Line Heater 4. In this article, we’ll walk you through the diagnostic steps, provide insights into the resistance values for DEF line heaters, and offer tips for effective troubleshooting.
What Does SPN 4357/FMI 5 – GHG14 Mean?
SPN 4357/FMI 5 – GHG14 is a diagnostic trouble code that usually points to an open circuit in Line Heater 4 of the DEF system. An open circuit means that the electrical path is interrupted, preventing the heater from functioning correctly. This can lead to issues with the DEF system, affecting the vehicle’s emissions and performance.
Step-by-Step Diagnostic Process
1. Check for Multiple Codes
Before diving into the diagnostics, it’s essential to check if there are multiple codes present:
- If SPN 4355/FMI 5 and SPN 4357/FMI 5 are both present, you should repair the open circuit between pin 15 of the ACM2.1 120-pin connector and pin 2 of line heaters 2 and 4.
- If only SPN 4357/FMI 5 is present, proceed to the next step.
2. Disconnect Line Heater 4
Disconnect Line Heater 4 to isolate it from the system for further testing.
3. Turn the Ignition ON
Turn the ignition to the ON position (key ON, engine OFF) to power the system for voltage measurements.
4. Measure Voltage at Pin 2
Measure the voltage between pin 2 on the harness side of the Line Heater 4 connector and ground:
- If the voltage is greater than 11.75V, move to the next step.
- If the voltage is less than 11.75V, repair the wire between pin 2 on the harness side of the Line Heater 4 connector and pin 15 of the ACM2.1.
5. Measure Voltage at Pin 1
Measure the voltage between pin 1 on the harness side of the Line Heater 4 connector and ground:
- If the voltage is between 2.25V and 2.50V, proceed to the next step.
- If the voltage is not within this range, repair the wire between pin 1 on the harness side of the Line Heater 4 connector and pin 32 of the ACM2.1.
6. Measure Resistance
Measure the resistance on the heating element side of Line Heater 4. Refer to the resistance chart below to ensure the values are within the specified range. If the resistance is not within the range, replace the line heating element.
Diesel Exhaust Fluid Line Heater Resistance Chart
| Length (mm) | Length (inches) | Nominal Resistance (ohms) | Min Resistance (ohms) | Max Resistance (ohms) |
|---|---|---|---|---|
| 500 | 19.6 | 16 | 12.8 | 19.2 |
| 1000 | 39.3 | 9.8 | 7.84 | 11.76 |
| 1200 | 47.2 | 8.6 | 6.88 | 10.32 |
| 1400 | 55.1 | 7.8 | 6.24 | 9.36 |
| 1600 | 62.9 | 7 | 5.6 | 8.4 |
| 1800 | 70.8 | 6.1 | 4.88 | 7.32 |
| 2000 | 78.7 | 5.6 | 4.48 | 6.72 |
| 2200 | 86.6 | 5.2 | 4.16 | 6.24 |
| 2400 | 94.4 | 4.9 | 3.92 | 5.88 |
| 2600 | 102.3 | 4.6 | 3.68 | 5.52 |
Conclusion
Diagnosing and repairing SPN 4357/FMI 5 – GHG14 requires a systematic approach. By following the steps outlined above and referring to the resistance chart, you can effectively troubleshoot and resolve issues with Line Heater 4 in your DEF system. Regular maintenance and timely repairs are crucial to ensure your vehicle’s emissions system operates efficiently, helping you stay compliant with environmental regulations and maintain optimal performance.
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