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.
Medium severity. Can I keep driving?Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
Symptoms
- Check engine or transmission warning lamp on
- Limp mode with a fixed gear, harsh or missing shifts
Most likely causes
- Pressure switch or sensor B faulty or stuck
- Sticking shift valve or dirt in the valve body
- Harness or connector at the gearbox: fluid wicking, corrosion, chafing
- Fluid level low or fluid contaminated
- Transmission control module faulty
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P0845 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 8: Transmission
- 45: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0845?
Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
What causes code P0845?
The most common causes are: pressure switch or sensor B faulty or stuck; sticking shift valve or dirt in the valve body; harness or connector at the gearbox: fluid wicking, corrosion, chafing.
Related codes
- P0846Transmission Fluid Pressure Sensor/Switch B Circuit Range/Performance
- P0847Transmission Fluid Pressure Sensor/Switch B Circuit Low
- P0848Transmission Fluid Pressure Sensor/Switch B Circuit High
- P0849Transmission Fluid Pressure Sensor/Switch B Circuit Intermittent
- P0840Transmission Fluid Pressure Sensor/Switch A Circuit
- P0768Shift Solenoid D Electrical
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.