Power steering loss while driving

Check your fluid levels, and go check if your 12v battery is good. Just a TIP, right now if you go onto Amazon and order the Panlong obd2 elm reader and click the promotion, you get a free battery tester with purchase! (Battery analyzer retails 50 bucks, and scan tool only costs you 10$)

 

It has electric power steering, so doesn't have power steering fluid, so this won't be the problem.

 

I was gonna ask about that but no need now.

So for the steering to quit, it would have had to cut power, to the pump (Power Steering Motor.) So it should have set a code?

 

Probably a C1511, C1512, C1513, or C1514.

You have a well-known Gen 1 issue. Back when there were more Gen 1s on the road it was a common topic here, but now it seems to be getting forgotten.

The power steering is (1) a torque sensor that detects how hard you are turning the wheel, fed into (2) a computer that factors that in along with the speed of the car (you don't need as much assist at higher speeds), to calculate (3) the amount of assistance to give you, which is fed to (4) an electric motor. In Gen 1, the torque sensor and the motor are both built into the steering rack underneath the car.

The torque sensor (one side of it) looks like this. The two places with parallel tracks of black material are potentiometers. Metal fingers from the other side of the sensor ride on those black tracks, and pick up a voltage that changes as the fingers move. The steering shaft is split right where the torque sensor is, with a slightly twistable torsion element between the two halves. So, the harder you turn the wheel, the further the upper shaft moves (just a tiny amount though) relative to the lower one, and the torque sensor fingers pick up a change in voltage, from which the steering computer knows which way you're turning the wheel and how hard.



The reason there are two potentiometers there is for redundancy. They are arranged so both give a mid-scale voltage when you're not turning the wheel, and when you do turn it, depending on the direction, one voltage goes up and the other goes down. The computer looks for that mirror-image relationship between the two voltages, or it decides it doesn't trust the sensor.

Gen 1 Prius used potentiometer sensors like that in a bunch of places: this steering torque sensor, the accelerator pedal, and the actuators that move the HVAC flaps around. They all had familiar problems when the contact surfaces got worn/dirty and the electrical resistance was no longer a smooth change from one end of the scale to the other. When it happens to the steering sensor, you get your steering gear jitters. When it happens to the accelerator pedal, you get the Big Hand Syndrome (feels like one has reached down from the sky and slowed down your car). When it happens to the HVAC actuators, you'll hear skittering sounds in the dash that aren't mice. They're all examples of the same kind of problem and fixed in the same kind of way, but by far the steering is hardest, only because getting the rack out is such a major project. Toyota had a warranty extension for it, but that's history now.

They changed to non-contact sensors using magnetic principles for the Gen 2 steering and pedal sensors, so those issues went away after Gen 1. Gen 2 could still get the skittery HVAC flaps; that design got changed in Gen 3.

When your steering torque sensor is noisy, the two mirror-image voltage signals won't both give a smooth measure of how hard you're turning the wheel. One or both of them might give a spiky noisy reading:



Sometimes, you'll notice the steering computer being fooled by the spiky readings, and you'll feel the wheel shaking or jumping as the computer thinks it is "assisting" you.

If your drive is long enough, the computer will eventually see enough readings that don't make sense, or aren't properly mirrored, so it says "that sensor is dodgy, I'm shutting off", and then you don't have steering assist for the rest of that drive. Turning the car off and back on will reset it. The worse the problem gets, the sooner the computer will call BS on the sensor and shut off. Mine at first would only do that toward the end of a 14 hour drive. Eventually it would happen on two-hour drives, and finally I went and had Toyota change out the rack under the extended warranty.

Because the system already gives you the most assist at low speeds (like maneuvering in a parking lot), and hardly any assist at roadway speeds where steering is easy, often if the steering assist cuts out while you're driving down the road, you'll hardly even notice until you come to an exit or a stop light, and then the steering feels hard for making a low-speed turn.