P0721 — Output speed sensor — range/performance
What it means: Output speed sensor — range/performance.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Inspect sensor
Don't risk it — look up listed providers near you and give them this code when you call.
Listed providers nearest Baltimore, MD
Closest first. Tell them P0721 and what the truck is doing. RoadService.app lists these providers and does not employ them or carry out the repair.
- 0.0 mi away — based in Baltimore, MD · (443) 680-6789
- 0.0 mi away — based in Baltimore, MD · (410) 544-3888
- 24 hour Mobile Diesel Truck Engine Repair DEF Repairs On Site Services Road Service Laptop Diagnostic Tractors & Dump Truck☎ Call0.0 mi away — based in Baltimore, MD · (443) 591-3631
What P0721 means
Output speed sensor — range/performance. Common causes: Sensor failing|Wiring|Tone wheel.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Sensor failing
- Wiring
- Tone wheel
First moves (roadside)
- Inspect sensor
FAQ
Output speed sensor — range/performance. Common causes: Sensor failing|Wiring|Tone wheel.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Sensor failing. Other possibilities include Wiring; Tone wheel.
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside P0721, or share the same subsystem.
- Main shaft speed erratic (SPN 160 FMI 2)
- Input shaft speed erratic (SPN 161 FMI 2)
- Transmission output retarder speed erratic (SPN 162 FMI 2)
- Trans oil temperature very high (SPN 177 FMI 0)
- Trans oil temperature voltage high (SPN 177 FMI 3)
- Trans oil temperature voltage low (SPN 177 FMI 4)
- Engine speed signal abnormal update rate (SPN 190 FMI 9)
- Transmission output shaft speed erratic (SPN 191 FMI 2)
Find a mechanic or related guides
General diagnostic guidance for diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack and more). Not a substitute for a scan-tool diagnosis on your specific truck.