SPN 973 FMI 5 — Engine retarder enable — open circuit
What it means: Engine retarder enable — open circuit.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Check output wiring
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Salt Lake City, UT
Closest first. Tell them SPN 973 FMI 5 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 Salt Lake City, UT · (801) 531-9256
- 0.0 mi away — based in Salt Lake City, UT · (385) 503-8084
- 0.0 mi away — based in Salt Lake City, UT · (385) 386-4700
Applies to: Bendix · Wabco · Stability control disables retarder on loss of traction
What SPN 973 FMI 5 means
Engine retarder enable — open circuit.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Wiring
- Output driver
- Driver
First moves (roadside)
- Check output wiring
- Check wiring
FAQ
Engine retarder enable — open circuit.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Wiring. Other possibilities include Output driver; Driver.
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 SPN 973 FMI 5, or share the same subsystem.
- Service brake air pressure — primary circuit low (SPN 519 FMI 4)
- Service brake air pressure — secondary circuit low (SPN 520 FMI 4)
- Left front wheel speed sensor erratic (SPN 789 FMI 2)
- Left front wheel speed abnormal signal (SPN 789 FMI 8)
- Right front wheel speed sensor erratic (SPN 790 FMI 2)
- Right front wheel speed abnormal (SPN 790 FMI 8)
- Left rear (LF drive) wheel speed erratic (SPN 791 FMI 2)
- Left rear wheel speed abnormal (SPN 791 FMI 8)
Same symptom: Won't shift
Other codes that show up as a truck that won't take a gear or drops out of one.
- Transmission output retarder speed erratic (SPN 162 FMI 2) · Drivetrain & Transmission
- Transmission output shaft speed erratic (SPN 191 FMI 2) · Drivetrain & Transmission
- Transmission output retarder position erratic (SPN 2919 FMI 2) · Drivetrain & Transmission
- Retarder not responding (SPN 2920 FMI 7) · Drivetrain & Transmission
- Gear selection failure (SPN 749 FMI 7) · Drivetrain & Transmission
- Range shift signal erratic (SPN 753 FMI 2) · Drivetrain & Transmission
Find a mechanic or related guides
General diagnostic guidance for heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.