Driveability
Plan around limited performance and avoid pushing the truck farther than necessary.
Medium urgencyMay require limp-home operation onlytransmission
SPN 3226 FMI 4: Transmission output speed – voltage low
Output speed sensor fault; can affect shift quality and cruise.
Transmission faults can affect shift quality, speed sensing, cruise behavior, and limp-home operation.
Module context
This code is currently grouped under the TCM so the assistant can frame likely causes and related systems faster.
Best next step
Capture the full fault list and operating condition before clearing anything. That gives the shop or roadside technician a much better starting point.
What symptoms often appear with SPN 3226 FMI 4
- Unexpected shift behavior or speed-related warnings
- Cruise control concerns after a transmission fault appears
- Limp-home behavior during road speed changes
Low-risk checks before shop-level diagnostics
- Note whether the fault appears at startup, under load, or during shifts.
- Avoid forcing the truck to continue if shift behavior is unpredictable.
- Record other dash warnings that appear with the speed-sensor complaint.
Related procedures and shop prep
No linked procedure is published for this code yet, but capturing the full code list and operating conditions still makes the next shop-level diagnostic step much stronger.
FAQ
Frequently asked questions about SPN 3226 FMI 4
What does SPN 3226 FMI 4 usually mean on a truck?
SPN 3226 FMI 4 commonly points to transmission output speed – voltage low. In TruckHelpNow, it is grouped under the transmission subsystem so drivers and shops can start with the most relevant checks first.
Can I keep driving with SPN 3226 FMI 4?
Plan around limited performance and avoid pushing the truck farther than necessary. The final decision should still depend on the full warning picture, related symptoms, and whether the truck is clearly safe to continue moving.
What should I collect before calling a shop about SPN 3226 FMI 4?
Collect the full code list, when the issue appears, what changed first, and any related warning lights or recent repairs. That context helps the next diagnostic step stay focused.