The Detroit DEF heater high document is a Detroit fault code reference that explains a Diesel Exhaust Fluid (DEF) line heater 5 circuit that has failed high, published for DD Series engines under SPN 5488 FMI 3 (GHG14). It gives workshop technicians the diagnostic sequence used to confirm the condition and return the truck to service, sourced from Detroit Power Service Literature.
Official document details
| Brand | Detroit (Detroit Diesel) |
| Model coverage | DD Series (EPA 2007-Current) and Series 60 (DDEC VI) |
| System / Group | Diagnostic Trouble Codes (DTCs) |
| Fault code | SPN 5488 / FMI 3 |
| Emissions family | GHG14 |
| Pages | 2 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification — SPN 5488 / FMI 3
- Output component test procedure
- Line heater / Dosing Unit harness inspection
- ACM2.1 wiring repair
- Dosing Unit 8-pin connector pinout
Troubleshooting the Detroit DEF heater high code
The procedure connects a diesel diagnostic tool, cycles the ignition and runs the Output Component Test, repeating it with an ignition cycle between attempts to confirm the fault. The line heater and Dosing Unit harness connector is then inspected for bent, spread or corroded pins, and a short to battery voltage between pin 3 of the 8-pin connector and pin 22 of the ACM2.1 120-pin connector is repaired; the document includes the full Dosing Unit 8-pin to ACM2.1 pin table.
Applicable truck models and engines
This diagnostic sheet applies to Detroit DD Series diesel engines built to EPA 2007 through current emissions standards, and the covered fault also appears on Series 60 (DDEC VI) applications listed in the source. Confirm the exact engine family and calibration against the vehicle before making repairs, and cross-check the specifications on the official Demand Detroit website.
Who needs this Detroit DEF heater high manual
Heavy-duty truck technicians, fleet maintenance staff and workshop owners diagnosing SPN 5488 FMI 3 with a diesel diagnostic tool will use this sheet to follow the correct steps rather than replacing parts by guesswork.
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