SPN 91 FMI 3 is the Detroit fault code for a circuit failed high 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 | 3 |
| Description | Circuit Failed High |
| Coverage / Revision | ALL YEARS |
| Pages | 1 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault code identification and description
- Accelerator Pedal (AP) harness voltage checks
- Common Powertrain Controller (CPC) circuit checks
- Repairing open circuits to the CPC
SPN 91 FMI 3 diagnostic overview
SPN 91 FMI 3 covers an accelerator pedal circuit-failed-high fault. The technician disconnects the AP, measures the B-to-C supply voltage, and where it is low, checks pin C to ground before repairing the open circuit to pin 4 or pin 8 of the CPC #1 connector. 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 3 manual
This document is aimed at Detroit DD Series technicians who need a concise single-page wiring check for a high-side accelerator pedal circuit fault.
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.
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