C1214 - Can I borrow that hammer, Karen?

I don't really think these sensors can get "stuck" in the same way that something like a throttle butterfly or relay contact can get stuck. In the US manual, each one has three wires, which appear to be power, ground, and signal. I suspect the sensors might be strain gauges, which don't have to move very much at all (like, thousandths of an inch) to produce a good amount of output. The US factory manual gives an output range of about 0.4 to 3.0 V, over an about an 0 to 12 MPa pressure range (0 to 1,700 psi).

One easy thing you could try is to unplug the suspect sensor and see if the car then reports 0 MPa, a million MPa, or throws a code. If it's still stuck at 1.3 MPa, then the harness or brake ECU is messed up.

I suspect the four connectors are keyed so this won't work, but you might be able to swap connectors between the problem sensor and a good sensor. If a different sensor reports as "stuck" on the scan tool, then it's the connector/harness/ECU. If the same sensor reports as "stuck" on the scan tool, then it's that sensor. If the connectors are keyed, maybe you can (carefully) use some jumper wires to do the same thing.

I don't think I'd hammer on anything. If you get it down to suspecting one sensor, it might not be a terrible idea to shut the car down, power down the brake system, and unscrew that sensor, to see if the business end is obviously beat up, or plugged up with crud, or the hole it goes in is plugged up with crud. This may also require a complicated bleeding procedure when you put it all back together, so proceed with care. (It may also be kind of useless if you can't buy the sensors loose piece.)

I don't know if the JDM model is the same as the US one, but it looks like you're starting down the factory manual path for C1214. Once it fails the "all readings change when you step on the pedal" test, the next thing is to plumb a mechanical pressure gauge into the brakes, and backprobe the wires for each sensor at the brake ECU while you step on the brakes. If that's no good, either the sensor wires are messed up or you replace the actuator. If that's OK, you make sure the brake light switch works, and if the switch is OK, replace brake ECU.

The manual also gives you a procedure for a "sensor test" you can do. You jump two pins on the OBD-II connector, start the car, the ABS warning light blinks. You let it sit not moving for at least 1 second, stomp on the brakes with at least 22 pounds of force, and then drive the car straight forward until it's going faster than 28 mph for several seconds. The ABS light goes out to tell you you're done. You then stop the car, jump two different pins on the OBD-II connector, and count the blinks. Mostly this is about the wheel speed sensors, but each of the four pressure sensors also has its own code (81,82,83,84).