P0845Transmission Fluid Pressure Sensor/Switch B Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Transmission fluid pressure sensor/switch A and B are inputs inside the automatic gearbox. 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.
- What you may notice
- Check engine or transmission warning lamp on
- Limp mode with a fixed gear, harsh or missing shifts
- Likely causes
- LikelyPressure switch or sensor B faulty or stuck
- PossibleSticking shift valve or dirt in the valve body
- PossibleHarness or connector at the gearbox: fluid wicking, corrosion, chafing
- PossibleFluid level low or fluid contaminated
- RareTransmission control module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.