This DEF air pressure drift sheet documents Detroit fault code SPN 4335 / FMI 2 on EPA10 engines, a sensor drift condition that sets the MIL. It compares the DEF air reading against barometric pressure to decide whether the sensor or the metering unit is at fault.
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 2 |
| Fault name | DEF air pressure sensor – drift |
| Emissions platform | EPA10 |
| Pages | 2 |
| File size | 0.2 MB |
| Format | |
| Language | English |
| Source | TruckFaultCodes.com (© 2017); Detroit Power Service Literature |
DEF air pressure drift sections covered
The two-page routine measures the pressure gap at key-on, then repeats it with the sensor removed to place the fault.
- Monitored parameter and enabling conditions; MIL lamp
- Compare DEF air pressure to barometric (Baro) and DEF pressure
- Check the reading stays within 28 kPa (4 psi)
- Remove the sensor and reconnect the harness
- Compare the pressures again to isolate the part
- Replace the metering unit, or replace the sensor
Applicable truck models
These steps cover Detroit DD-Series (DD13, DD15 and DD16) and Series 60 DDEC VI engines on the EPA10 platform with the ACM2 aftertreatment control module. Removal and installation chapters are held in Detroit Power Service Literature at the Detroit Diesel official website.
Who needs this air pressure drift manual
This air pressure drift manual is for technicians resolving SPN 4335 / FMI 2, where a comparison against barometric pressure, not a simple ohm check, is what separates a drifted sensor from a bad metering unit.
The full 2-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 2 in Power Service Literature, and technicians should keep the wiring pin numbers shown in this sheet on hand while testing on the bench.
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