SPN 797 FMI 6 — Modulator valve — left front — short to ground
What it means: Modulator valve — left front — short to ground.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Disconnect valve and measure
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Louisville, KY
Closest first. Tell them SPN 797 FMI 6 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 Louisville, KY · (502) 773-1159
- 0.0 mi away — based in Louisville, KY · (502) 447-1234
- 0.0 mi away — based in Louisville, KY · (502) 648-6725
Applies to: Bendix · Wabco
What SPN 797 FMI 6 means
Modulator valve — left front — short to ground.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Shorted valve
- Wire ground
- Short
First moves (roadside)
- Disconnect valve and measure
- Disconnect and measure
FAQ
Modulator valve — left front — short to ground.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Shorted valve. Other possibilities include Wire ground; Short.
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 797 FMI 6, or share the same subsystem.
- Modulator valve — left front — open (SPN 797 FMI 5)
- 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)
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.