SPN 520249 FMI 4 is the Detroit Diesel fault-code service sheet that documents an SCR inlet temperature-high reading in the aftertreatment system. It documents the monitored parameter, engine reaction, and the harness and sensor checks that follow. This DiagTechPro library page summarizes what the 1-page PDF contains so a technician can confirm it is the right document before downloading.
Official document details
| Brand | Detroit (Detroit Diesel) |
|---|---|
| Model coverage | DD Series (EPA 2007-Current); Series 60 DDEC VI (EPA 2007) |
| System / group | EPA10 diagnostic trouble codes |
| Suspect Parameter Number | 520249 |
| Failure Mode Identifier | 4 |
| Source | TruckFaultCodes.com, © 2017 |
| Pages | 1 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Monitored parameter and enabling conditions
- Engine reaction: 25% derate, MIL and CEL
- Step 2: check for SPN 3246/FMI 15
- Step 3: AS095 voltage wiggle test
- Steps 4-5: connector inspection and sensor replacement
SPN 520249 FMI 4 diagnostic summary
The document lists the monitored parameter as SCR inlet temperature, always enabled, evaluated continuously with a typical two-second duration, illuminating the MIL and CEL and producing a 25% derate, with parked regeneration used for verification. Diagnosis starts by confirming whether SPN 3246/FMI 15 (DPF outlet over-temperature) is also present, then monitors the AS095 SCR inlet temperature voltage during a harness wiggle test. If no sudden voltage changes appear, the technician inspects the SCR inlet temperature sensor connector for bent, spread or corroded pins before replacing the sensor.
Applicable Detroit truck models
This fault-code sheet applies to Detroit DD Series engines certified to EPA 2007 and later emissions standards, and it is cross-listed under the Detroit Series 60 (DDEC VI, EPA 2007) diagnostic set. For full engine specifications and support details, see the official Detroit website.
Who needs this SPN 520249 FMI 4 manual
Aftertreatment and emissions technicians working on Detroit DD Series trucks rely on this sheet to trace a temperature-high derate to a harness, connector or sensor fault without guesswork.
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