P0845 code meaning
Transmission Fluid Pressure Sensor/Switch B Circuit
Powertrain system Generic code P08xx codes Check engine light
What P0845 means
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.
P0845 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1.5 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0845
- Check engine or transmission warning lamp on
- Limp mode with a fixed gear, harsh or missing shifts
Common causes of P0845
- Most 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
- Less likelyTransmission control module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transmission fluid pressure sensorTransmission valve bodyTransmission wiringTransmission control module
What each part of P0845 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 8 | Area: transmission. |
| 45 | The exact fault in that area. |
What to do next
- Note P0845 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0845
What does P0845 mean?
P0845 means "Transmission Fluid Pressure Sensor/Switch B Circuit". Transmission fluid pressure sensor/switch A and B are inputs inside the automatic gearbox. It is a generic code, so it means the same on every make.
Is it safe to drive with P0845?
Drive gently and only to a workshop. With P0845 the car can go into limp mode (reduced power) to protect itself.
Will P0845 fail an emissions test?
Yes, it can. P0845 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0845 to fix?
Difficulty: hard. A typical repair takes 1.5 to 5 hours of work. This is a job for a workshop.
Will P0845 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.