SPN 91 FMI 8 is the Detroit fault code for a general fault if channel 1 signal cannot be used on the DD Series accelerator pedal circuit. This 1-page reference from the DiagTechPro library reproduces the official Detroit troubleshooting steps so a technician can work the fault in the correct order. It is a factory-style diagnostic guide, not a repair shortcut.
Official document details
| Brand | Detroit (Detroit Diesel) |
| Model coverage | DD13, DD15, DD16 – DD Series (EPA 2007–current) |
| System / Group | DD Series (EPA 2007-Current) / DTCs |
| Suspect Parameter Number | 91 |
| Failure Mode Identifier | 8 |
| Description | General Fault If Channel 1 Signal Cannot Be Used |
| Coverage / Revision | GHG14 |
| Pages | 1 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification and description
- Disconnecting the Accelerator Pedal (AP)
- Key-on ignition preparation steps
SPN 91 FMI 8 diagnostic overview
SPN 91 FMI 8 flags a general fault when the channel 1 signal of the two-channel accelerator pedal cannot be used. The short procedure starts by disconnecting the Accelerator Pedal and turning the ignition on with the engine off, setting up the pedal supply and signal checks that follow. Each step is written as a yes or no decision, so the result of one measurement points directly to the next check or to the final repair action.
Applicable truck models and engines
It applies to Detroit DD13, DD15 and DD16 engines in the DD Series (EPA 2007 to current) family, and the library also carries the matching guide for the Series 60 (DDEC VI) platform. For factory support tools and warranty information, see Demand Detroit official resources.
Who needs this 91 FMI 8 manual
This document helps Detroit DD Series technicians begin an accelerator pedal channel-1 diagnosis correctly, with the initial disconnect and key-on steps in the right order.
The full PDF is available in the DiagTechPro manuals library; a free account is required to download it, view every page, and print the decision steps for use at the workshop bench.
Related manuals library
