SPN 520328 FMI 7 is a Detroit DD Series diagnostic fault-code sheet that documents the Diesel Exhaust Fluid (DEF) System Has Been Over Pressurized condition and its factory troubleshooting sequence. The sheet lists the SPN and FMI identifiers, a short description of the condition, and the repair steps in the order Detroit recommends. It is a concise reference sheet, 4 pages long, aimed at technicians who read the code with a scan tool and need to know the correct next step.
SPN 520328 FMI 7 troubleshooting overview
This four-page sheet covers a Diesel Exhaust Fluid (DEF) system that has been over pressurized. After ruling out companion SPN 4334 and SPN 4374 faults, the technician inspects the DEF dosing unit, DEF pump, ATS 47-pin and ACM2.1 connectors, performs return-line flow tests through the SCR ADS self-check, and works up to replacing the DEF dosing unit, DEF pump or ACM2.1.
Official document details
| Brand | Detroit (Detroit Diesel) |
| Model coverage | DD Series (EPA 2007-Current) |
| System / group | Diagnostic Trouble Codes (DTCs) |
| SPN | 520328 |
| FMI | 7 — Diesel Exhaust Fluid (DEF) System Has Been Over Pressurized |
| Source | TruckFaultCodes.com fault-code reference (Copyright 2017) |
| Pages | 4 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification: SPN and FMI header
- Step 1–3: connect the diagnostic tool and check for SPN 4334/4374 companion faults
- Step 4–12: inspect DEF dosing unit, DEF pump, ATS 47-pin and ACM2.1 harness connectors
- Step 13–19: return-line flow tests and DEF tank header/supply filter inspection
- Step 20–22: replace the DEF pump and test the ACM2.1
Applicable truck models
This code sheet applies to Detroit DD Series engines (DD13, DD15 and DD16) built to GHG14 emissions specifications under the EPA 2007-Current platform, and Detroit cross-lists it under both the DD Series and Series 60 (DDEC VI, EPA 2007) diagnostic trees. For factory service literature and warranty details, refer to the official Detroit Diesel website.
Who needs this SPN 520328 FMI 7 manual
This reference is written for aftertreatment technicians resolving repeat DEF over-pressure faults who need the full connector, flow-test and component-replacement path. Keep the 520328 FMI 7 sheet on hand so the code can be diagnosed and verified before it is cleared.
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