This DEF metering unit heater sheet covers Detroit fault code SPN 4353 / FMI 3 on EPA10 engines, where the diffuser heater circuit has failed high. The procedure verifies the fault with an Output Component Test, then measures resistance to separate a short to battery from a bad heater.
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 4353 / FMI 3 |
| Fault name | DEF metering unit diffuser heater circuit failed high |
| Emissions platform | EPA10 |
| Pages | 2 |
| File size | 0.2 MB |
| Format | |
| Language | English |
| Source | TruckFaultCodes.com (© 2017); Detroit Power Service Literature |
DEF metering unit heater sections covered
The two-page routine confirms the code, inspects the connector, and reads a specific ohm window across the heater.
- Fault code header: SPN 4353, FMI 3
- Connect the diesel diagnostic tool and perform the Output Component Test
- Repeat the test three times, cycling ignition between each run
- Disconnect the diffuser heater harness connector and inspect pins
- Measure resistance across the heater (9 to 13.5 ohms)
- Repair the short to battery at ACM2 pin 22, or replace the diffuser heater
Applicable truck models
The document applies to Detroit DD-Series (DD13, DD15 and DD16) and Series 60 DDEC VI engines on the EPA10 platform with the ACM2 aftertreatment control module. Component removal is described under “Removal of the Diesel Exhaust Fluid Metering Unit Diffuser Heater” in Detroit Power Service Literature at the Detroit Diesel official website.
Who needs this DEF metering unit heater manual
This metering unit heater manual is aimed at technicians resolving SPN 4353 / FMI 3, giving the exact test sequence and 9 to 13.5 ohm target so the repair is right the first time.
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 4353 / FMI 3 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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