What P0845 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. P0845 is the general circuit fault of switch or sensor B. In GM's 2006 Allison table it belongs to the switch on shift valve S2: if the switch reports pressure for more than 0.04 s with the valve at rest, the valve is commanded again; if the fault persists, the case is classed as electrical (with P0768), mechanical or sporadic. Type A, MIL after one trip.
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
- Limp mode with a fixed gear, harsh or missing shifts
Common causes
- Pressure switch or sensor B faulty or stuck Most likely
- Sticking shift valve or dirt in the valve body Possible
- Harness or connector at the transmission: fluid wicking, corrosion, chafing Possible
- Fluid level low or fluid contaminated Possible
- Transmission control module faulty Less likely
How to diagnose P0845
- 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 P0845 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Honda Odyssey | 2002–2003 | 3 | 68k |
Counts of owner complaints to the NHTSA that mention P0845 (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
- 45
- Specific fault
Questions drivers ask
Can I drive with code P0845?
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 P0845?
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.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0845. They can point to a shared cause, so it's worth checking them together.
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.