P0791
Intermediate Shaft Speed Sensor "A" Circuit
- Severity
- High
- Driving
- Drive only to a garage
A fault in the circuit for the intermediate shaft speed sensor "A", which tells the module how fast an intermediate shaft inside the transmission is turning. That matters because on transmissions with more gears, the module uses it to verify which clutches are actually applied. Without it the module cannot verify what the transmission is doing, so it will usually stop shifting normally and hold a single gear.
Possible causes
- CommonFailed speed sensor
- CommonCorroded connector or wiring damage at the sensor
- CommonMetal debris on the sensor tip, from internal wear
- PossibleDamaged or contaminated reluctor ring the sensor reads
- PossibleInternal transmission harness failure
- PossibleSensor air gap wrong after a previous repair
What you might notice
- Transmission stuck in one gear - limp mode
- Harsh or erratic shifting
- Speedometer inoperative or erratic on vehicles that take speed from this sensor
- Cruise control unavailable
- Check engine light on
What to check, in order
- Watch the speed readings on the live data screen while driving. Input and output speed should track each other in a fixed ratio in each gear; one that reads zero or jumps about names itself.
- Inspect the sensor tip for a coating of metal filings. Debris here is not just the fault - it is evidence of internal wear that will need addressing.
- Check the connector and wiring at the sensor for corrosion and chafing.
- Check the fluid level and condition.
- If the sensor is accessible, measure its resistance against specification.
- Where the sensor is internal, eliminate the external wiring and the case connector before dropping the pan.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Transmission
P0700P0701P0702P0703P0704P0705P0706P0707P0708P0709P0710P0711P0712P0713P0714P0715P0716P0717P0718P0719P0720P0721P0722P0723P0724P0725P0726P0727P0728P0729P0730P0731P0732P0733P0734P0735P0736P0737P0738P0739P0740P0741P0742P0743P0744P0745P0746P0747P0748P0749P0750P0751P0752P0753P0754P0755P0756P0757P0758P0759P0760P0761P0762P0763P0764P0765P0766P0767P0768P0769P0770P0771P0772P0773P0774P0775P0776P0777P0778P0779P0780P0781P0782P0783P0784P0785P0786P0787P0788P0789P0790P0791P0792P0793P0794P0795P0796P0797P0798P0799