If you're trying to track down the p0845 transmission fluid pressure sensor/switch b circuit location, you're likely dealing with a car that's acting like it forgot how to shift. It's a frustrating spot to be in, especially when your dashboard is lit up like a Christmas tree and the transmission is sticking in one gear or jerking every time you hit the gas. Finding the sensor is the first step toward getting things back to normal, but it's not always as simple as looking under the hood.
Most of the time, this specific sensor—often called the "B" sensor or Switch 2—is tucked away inside the transmission itself. It's part of a system that tells your car's computer how much hydraulic pressure is moving through the lines. When the computer (the PCM or TCM) stops getting a clear signal from this "B" circuit, it freaks out and throws the P0845 code.
Where is the P0845 sensor usually hiding?
To be honest, the exact spot depends heavily on what you're driving. If you're looking for the p0845 transmission fluid pressure sensor/switch b circuit location in a Nissan, which is one of the most common vehicles to have this issue, you'll usually find it mounted on the valve body. This means you've got to drain the transmission fluid and pull the bottom pan off just to see it. It's not exactly a "five-minute fix" in the driveway.
In some other makes, like certain Hondas or older Chryslers, the sensor might actually be external. In those lucky cases, you'll see it threaded into the transmission case, looking a bit like a spark plug with a wire coming out of the end. You can usually spot these by looking through the driver-side wheel well or reaching down past the airbox. But if your car has a CVT (Continuously Variable Transmission), prepare yourself to get a little messy, because that sensor is almost certainly internal.
Why the "B" circuit matters
You might be wondering why there's an "A" and a "B." Think of your transmission as a complicated plumbing system. The computer needs to know the pressure at different points to make sure the "pipes" are moving the fluid correctly to change gears. "Sensor B" is just one specific checkpoint in that plumbing.
When you get a P0845 code, the computer isn't necessarily saying the sensor is "broken." It's saying the circuit is wrong. That's a small but huge distinction. It could be the sensor, sure, but it could also be a pinched wire, a corroded plug, or even just really dirty fluid that's gunking up the works.
Common symptoms you'll notice
- The Check Engine Light: Obviously, this is your first clue.
- Limp Mode: Your car might lock itself into second or third gear to prevent you from blowing something up.
- Hard Shifting: It feels like someone is kicking the back of your seat every time the car shifts.
- Poor Fuel Economy: If the transmission can't find the right gear, the engine works harder than it needs to.
Is it a DIY job to find and fix it?
Whether you should tackle this yourself really depends on your comfort level with getting covered in transmission fluid. If the p0845 transmission fluid pressure sensor/switch b circuit location on your specific car is external, then yeah, it's basically like changing a sensor on an engine. You unplug it, unscrew it, put the new one in, and you're done.
However, if it's internal, you're looking at a bigger project. You'll need to: 1. Drain the fluid (which is always a mess). 2. Remove the transmission pan bolts. 3. Carefully lower the pan without drenching yourself in the remaining oil. 4. Locate the sensor on the valve body (the big "brain" looking thing with all the channels). 5. Swap the sensor and put it all back together with a new gasket.
If you've never done a transmission service before, this can be a bit intimidating. The bolts are small, and if you over-tighten them, you're going to have a bad time.
Don't ignore the wiring and connectors
Before you go out and buy a new sensor, check the wiring harness. This is a pro tip that saves people hundreds of dollars. The p0845 transmission fluid pressure sensor/switch b circuit location includes the entire path from the sensor to the computer.
I've seen plenty of cases where a squirrel or a mouse decided to have a snack on the wires leading into the transmission. Or, sometimes the plastic connector gets brittle from the heat of the engine and snaps, leading to a loose connection. Give the wires a good wiggle and look for any green crusty stuff (corrosion) inside the plugs. A little bit of electrical cleaner can sometimes "fix" a P0845 code faster than a new part ever could.
The role of transmission fluid quality
It's also worth mentioning that your fluid might be the real culprit. If your transmission fluid is old, burnt, or full of tiny metal shavings, it can physically block the sensor's ability to read pressure. If the fluid can't get into the sensor, the sensor reports "low or no pressure," and the computer throws the code.
If you pull your dipstick (if your car still has one) and the fluid looks like black coffee instead of bright red cherry juice, you might want to try a fluid change first. Sometimes fresh, clean fluid is all it takes to clear the p0845 transmission fluid pressure sensor/switch b circuit location error.
What about the "Switch B" part?
In some manuals, you'll see this referred to as a "switch" rather than a "sensor." Functionally, they do the same thing for you—they report pressure. A switch is usually "on or off" (meaning pressure is either there or it isn't), while a sensor provides a range of data. Regardless of the terminology your car manufacturer uses, the troubleshooting steps remain the same.
Final thoughts on fixing the P0845
Dealing with transmission codes is never a fun Saturday afternoon. But once you've identified the p0845 transmission fluid pressure sensor/switch b circuit location, the mystery is mostly solved. Whether you choose to dive into the transmission pan yourself or you decide to hand a mechanic a pile of money to do it for you, at least you know what you're looking at.
Just remember to check the simple stuff first. Look at the wires, check the fluid level, and make sure your battery is in good shape (low voltage can cause all sorts of fake sensor codes). If all those are fine, then it's time to get that sensor replaced and get your smooth ride back. It's a bit of a hassle, but once it's fixed, your car will feel like a completely different machine.