What P0846 means
Transmission fluid pressure sensor/switch A and B are inputs inside the automatic transmission.
How the engine computer detects it
A switch only reports pressure present or absent, a sensor reports a value. The letter is the maker's choice: Allison 1000 uses A and B for the switches on shift valves S1 and S2, GM's CVT for the primary and secondary pulley sensors, GM's 2025 8-speed A for the lube pressure sensor; Ford reports pressure faults under its solenoid codes instead. P0846 is the plausibility fault of B. GM's CVT uses the same test as for A on its second pulley: pressure off target by 500 or 1500 kPa (218 psi) plus a ratio error above 0.2 for about 6 s, line pressure above 600 kPa (87 psi), over 35 km/h (22 mph), type A. Allison sets it when switch 2 stays without pressure 5 s after valve S2 is applied. On the Corvette dual clutch a sticking valve is the usual cause.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine or transmission warning lamp on
- Slipping or shift shock
- CVT: ratio and power limited
Common causes
- Dirty or sticking valve, worn valve body Most likely
- Pressure sensor or switch drifting or sticking Most likely
- Fluid level low, fluid aged or filter clogged Possible
- Mechanical damage: thrust washer, CVT belt or pulley, pump Possible
- Control module software Less likely
How to diagnose P0846
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: transmission fluid pressure sensor, transmission valve body, transmission wiring, transmission control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report P0846 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Nissan Sentra | 2015–2019 | 3 | — |
Counts of owner complaints to the NHTSA that mention P0846 (6 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 8
- Transmission
- 46
- Specific fault
Questions drivers ask
Can I drive with code P0846?
If the car shifts normally, drive gently to a shop. If it's stuck in one gear, slips, shifts harshly or won't move out of Park, don't drive it: have it towed.
Will my car pass an emissions inspection with P0846?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.