SPN 520327 FMI 4 is a Detroit DD Series diagnostic fault-code sheet that documents the Over Pressurized Diesel Exhaust Fluid (DEF) System 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, 3 pages long, aimed at technicians who read the code with a scan tool and need to know the correct next step.
SPN 520327 FMI 4 troubleshooting overview
This three-page sheet covers an over pressurized Diesel Exhaust Fluid (DEF) system, monitored on DEF pump speed versus DEF pressure with the CEL illuminated. After ruling out companion SPN 4334 and SPN 4374 faults, the technician inspects the DEF dosing unit and pump harness, checks the DEF lines, purges the return line and runs the SCR ADS self-check.
Official document details
| Brand | Detroit (Detroit Diesel) |
| Model coverage | DD Series (EPA 2007-Current) |
| System / group | Diagnostic Trouble Codes (DTCs) |
| SPN | 520327 |
| FMI | 4 — Over Pressurized Diesel Exhaust Fluid (DEF) System |
| Source | TruckFaultCodes.com fault-code reference (Copyright 2017) |
| Pages | 3 |
| File size | 0.3 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification and description (DEF pump speed vs. DEF pressure, CEL)
- Step 1–4: check companion SPN 4334/4374 faults and inspect DEF dosing unit and pump harness
- Step 5–6: inspect DEF lines and purge the return line with clean shop air
- Step 7: SCR ADS self-check — DEF pump speed 750–1800 rpm, DEF pressure 9000–11000 mbar (130–160 psi)
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 520327 FMI 4 manual
This reference is written for aftertreatment technicians servicing high DEF pressure faults who need the harness inspection and SCR ADS self-check values. Keep the 520327 FMI 4 sheet on hand so the code can be diagnosed and verified before it is cleared.
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