This DEF air pressure sensor sheet documents Detroit fault code SPN 4335 / FMI 4 on EPA10 engines, a metering-unit circuit-failed-low condition with a 25% derate. It first checks for related codes, then measures resistance to ground to separate a shorted wire from a failed sensor.
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 4 |
| Fault name | DEF metering unit air pressure sensor circuit failed low |
| Emissions platform | EPA10 |
| Pages | 2 |
| File size | 0.2 MB |
| Format | |
| Language | English |
| Source | TruckFaultCodes.com (© 2017); Detroit Power Service Literature |
DEF air pressure sensor sections covered
The two-page routine uses a multi-code screen to catch shared-wiring faults before the isolated resistance check.
- Monitored parameter and 25% engine derate; MIL and CEL
- Check for SPN 4335, 4334 and 3510 FMI 4 present together
- Repair the shared short to voltage or ground at ACM2 pin 84
- Disconnect the sensor and the ACM2 120-pin connector
- Measure resistance to ground (less than 1K ohms)
- Repair the wire to ACM2 pin 74, 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 follows the metering-unit air pressure sensor chapter in Detroit Power Service Literature at the Detroit Diesel official website.
Who needs this DEF air pressure sensor manual
This air pressure sensor manual is for technicians clearing SPN 4335 / FMI 4, showing how a group of related codes points to shared wiring so a good sensor is not replaced by mistake.
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 4 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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