P0791 and related codes: intermediate shaft, turbine B and engine speed signals
A speed sensor on an intermediate shaft (A, B or C) or a second input or turbine sensor (B) has a circuit fault, no signal or an implausible reading, the two input sensors disagree, or the engine speed signal into or out of the gearbox computer is wrong.
SeverityModerateUsually not urgent today, but it can get worse if left.
Can you keep driving?Drive gently, check it soonWhat does P0791 mean?
Larger automatic gearboxes measure more than input and output speed: sensors on intermediate shafts and a second turbine sensor let the computer check each clutch as it applies. The gearbox computer also needs the engine speed, either read directly (P0725 to P0728) or passed on to other modules (P0737 to P0739). Without one of these signals the computer cannot judge a change, so it falls back to firm, fixed shift patterns or a single gear.
What causes P0791?
- A failed speed sensor or a damaged wire to it
- A sensor tip covered in metal particles from gearbox wear
- Fluid inside the sensor connector
- A crankshaft speed signal problem upstream, for the engine speed codes
- A damaged reluctor ring on the shaft the sensor reads
What to check first for P0791
- If ratio codes appear together with these, fix the speed sensor first and test again
- For the engine speed codes, check whether the engine computer also has a crankshaft sensor code
- Watch the speed signals live on a scan tool while driving gently
- Inspect the sensor connectors and look for metal on the sensor tips
Can you drive with P0791?
Usually you can drive gently to a workshop. Expect harsh changes or a fixed gear, and stay off fast roads and avoid heavy loads until it is fixed.
In states with an OBD-II emissions inspection, a car with the check engine light on fails the test until the fault is fixed.
Codes on this page
24
- P0725Engine Speed Input Circuit
- P0726Engine Speed Input Circuit Range/Performance
- P0727Engine Speed Input Circuit No Signal
- P0728Engine Speed Input Circuit Intermittent
- P0737TCM Engine Speed Output Circuit
- P0738TCM Engine Speed Output Circuit Low
- P0739TCM Engine Speed Output Circuit High
- P0791Intermediate Shaft Speed Sensor "A" Circuit
- P0792Intermediate Shaft Speed Sensor "A" Circuit Range/Performance
- P0793Intermediate Shaft Speed Sensor "A" Circuit No Signal
- P0794Intermediate Shaft Speed Sensor "A" Circuit Intermittent
- P2745Intermediate Shaft Speed Sensor "B" Circuit
- P2746Intermediate Shaft Speed Sensor "B" Circuit Range/Performance
- P2747Intermediate Shaft Speed Sensor "B" Circuit No Signal
- P2748Intermediate Shaft Speed Sensor "B" Circuit Intermittent
- P2749Intermediate Shaft Speed Sensor "C" Circuit
- P2750Intermediate Shaft Speed Sensor "C" Circuit Range/Performance
- P2751Intermediate Shaft Speed Sensor "C" Circuit No Signal
- P2752Intermediate Shaft Speed Sensor "C" Circuit Intermittent
- P2765Input/Turbine Speed Sensor "B" Circuit
- P2766Input/Turbine Speed Sensor "B" Circuit Range/Performance
- P2767Input/Turbine Speed Sensor "B" Circuit No Signal
- P2768Input/Turbine Speed Sensor "B" Circuit Intermittent
- P2784Input/Turbine Speed Sensor "A"/"B" Correlation
Related codes
Checked on · Rafael Soares
These are the generic meanings every manufacturer shares. Each brand adds its own detail, so your car's handbook, its service information and a qualified mechanic have the last word. OdoKeep has no connection with any manufacturer, and the app does not read codes from the car.
