This metering unit air pressure document covers Detroit fault code SPN 4335 / FMI 7 on EPA10 engines, a low-pressure condition that sets the MIL. The nine-page procedure checks vehicle air, gauges the SCR test, and clears DEF crystals from the diffuser and air supply screen.
Official document details
| Brand | Detroit |
| Model coverage | Detroit DD-Series (DD13, DD15, DD16) and Series 60 (DDEC VI) |
| System / Group | DD Series (EPA 2007-Current) / DTCs |
| Fault code | SPN 4335 / FMI 7 |
| Fault name | DEF metering unit low air pressure |
| Emissions platform | EPA10 |
| Pages | 9 |
| File size | 0.6 MB |
| Format | |
| Language | English |
| Source | TruckFaultCodes.com (© 2017); Detroit Power Service Literature |
metering unit air pressure sections covered
The long routine follows the air path end to end, from the tank and limiting unit through the metering diffuser to a final pressure verification.
- Confirm vehicle air pressure reaches 689 kPa (100 psi)
- Compare the reading to barometric (Baro) and DEF pressure
- Inspect supply lines and pressure limiting unit orifices
- Gauge the SCR test at 537 to 586 kPa (78 to 85 psi)
- Inspect and flush the compressed air supply screen and diffuser heater
- Verify 131 to 200 kPa (19 to 29 psi) or contact Detroit support
Applicable truck models
These steps cover Detroit DD-Series (DD13, DD15 and DD16) and Series 60 DDEC VI engines on the EPA10 platform served by the ACM2 aftertreatment control module. Diffuser and screen removal chapters are in Detroit Power Service Literature at the Detroit Diesel official website.
Who needs this metering unit air pressure manual
This manual is for the technician chasing a low reading on SPN 4335 / FMI 7, where a plugged diffuser or a contaminated supply screen, not just a sensor, is often the real cause behind the pressure loss on this nine-page procedure.
The full 9-page PDF is available in the DiagTechPro manuals library; a free account is required to download. For workshop reference, Detroit documents the matching component removal and installation steps for SPN 4335 / FMI 7 in Power Service Literature, and technicians should keep the wiring pin numbers shown in this sheet on hand while testing on the bench.
Related manuals library
