The Detroit ACM communication fault troubleshooting sheet documents Detroit fault code SPN 1231 FMI 9, which sets when the Aftertreatment Control Module (ACM) message is not received or has stopped arriving. This 6-page PDF belongs to the Detroit DD Series (EPA 2007-Current) DTC library and guides a technician through the confirmation and repair sequence for the code. It is drawn from Detroit Power Service Literature and republished by TruckFaultCodes.com (2017).
Across six pages the sheet checks battery-voltage faults and recent programming, measures the PTCAN terminating-resistor values at the MCM, ACM and CPC connectors, verifies continuity of the powertrain CAN wiring between those modules, and finally confirms the voltage and ground supplied to the ACM 21-pin connector.
Detroit ACM communication fault document details
| Brand | Detroit |
| Model coverage | DD Series (EPA 2007-Current) |
| System / Group | Diagnostic Trouble Codes (DTCs) |
| Fault code | SPN 1231 FMI 9 |
| Source | Detroit Power Service Literature |
| Pages | 6 |
| File size | 0.5 MB |
| Format | |
| Language | English |
Document table of contents
- Battery voltage fault check (SPN 168)
- ACM / MCM / CPC programming check
- PTCAN terminating resistor measurements
- Continuity checks between CPC, ACM and MCM
- ACM voltage and ground verification
Applicable truck models
This fault code troubleshooting procedure applies to Detroit DD Series engines built to EPA 2007 and later emissions standards, covering EPA10 and GHG14 configurations within the DD Series DTC set. Use it alongside a diesel diagnostic tool such as DiagnosticLink or ServiceLink to read live data and confirm the code before any parts are replaced. For engine coverage and official service resources, visit the Detroit Diesel official website.
Who needs this Detroit ACM communication fault manual
Fleet technicians, mobile diesel mechanics and workshop owners rely on this reference before opening the SPN 1231 FMI 9 code with a scan tool. Following the documented sequence avoids replacing good parts and clarifies whether the concern lies in wiring, a sensor, or a mechanical component.
The full SPN 1231 FMI 9 PDF is available in the DiagTechPro manuals library; a free account is required to download.
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