SPN 520250 FMI 4 is the Detroit Diesel fault-code service sheet that documents a Quantity Control Valve (QCV) low-side driver error. It provides the resistance and voltage checks that separate a valve fault from a harness short. This DiagTechPro library page summarizes what the 2-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 | 520250 |
| Failure Mode Identifier | 4 |
| Source | TruckFaultCodes.com, © 2017 |
| Pages | 2 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Description: MCM pin 2 short or internal QCV short
- Steps 1-3: DVOM resistance test of the QCV
- Step 4: inspect the 120-pin MCM connector
- Steps 5-6: pin 2 voltage check
SPN 520250 FMI 4 diagnostic summary
The sheet explains the condition can occur when the MCM pin 2 circuit is shorted to power or when the quantity control valve has an internal short. Diagnosis begins by disconnecting the QCV harness connector and measuring resistance across pins 1 and 2 with a DVOM: below 1.3 ohms indicates a failed valve, while a reading between 1.3 and 1.4 ohms sends the technician on to inspect the 120-pin Motor Control Module connector for corroded, bent or broken pins. A final voltage check at pin 2 of the harness distinguishes an MCM replacement from a short to battery.
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 520250 FMI 4 manual
Detroit diesel technicians diagnosing a rail-pressure or fuelling driver fault use this sheet to test the quantity control valve and MCM circuit correctly before replacing either part.
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