2001 Power Steering Issue; Battery related?

I wouldn't guess that battery condition or being in reverse would be likely causes. You're probably seeing it more in reverse because when you're in reverse you're probably more likely to be (a) driving slowly and (b) steering markedly, and the steering computer is set up to give you more amplification at lower speeds, which also means more amplification of iffy signals.

How the signals get iffy is fairly well understood and is a thing that happens with these cars. Unfortunately the sensor is built deeply into the steering gear and once you get too annoyed to put up with it, there doesn't seem to be much for it but to replace the gear unit.

You can have a few stages of severity:

1. no warning lights or codes, but you occasionally notice steering shudders when making low speed manuevers e.g. parking. My car is in this stage, and has been for ~40000 miles without getting noticeably worse. In this stage you might notice that simply keeping a good two-hand grip on the wheel when maneuvering that way can make the problem appear to be cured completely. (i.e. it's not just that your tight grip allows you to fight the shudder--keeping your arms coupled to the wheel actually damps a resonance that contributes to the shudder in the first place.)

2. Occasional shudders and warning lights and codes. This sounds like where your car is now. It can be managed the same way as (1) but is obviously farther along on the way to (3).

3. The torque signal gets so noisy that the steering ecu says "warning, schmarning, I'm turning off!" pretty much all the time, and you have non-power-assisted steering.

There may be some relief on the price of the replacement steering gear by getting a reman one from Cardone - I noticed a couple years ago that they offer one, but I haven't seen anyone here report experience with it.

Some people reportedly just unplug the power steering system and enjoy a manual-steering Prius.

There was more information in some old threads like this one.

Hope this helps,
-Chap

 

Definitely not something to take to the dealer. Any chance you have a good hybrid shop nearby? Preferred Independent Hybrid Car Repair and Service Shops | Hybrid Cars

 

The ideal would be to install a functioning EMPS assembly. Price could be as fresh quotes, or less via aftermarket parts shops. Check this please.

Pull the EMPS fuse and drive your car 'without' power steering. Very easy at highway speeds but requiring 'adult strength' for parking or at low driving speeds. By no means would it be crazy to drive an NHW11 in this way. Actually I did it with mine for some time.

It may be that you can delay the inevitable by working the steering from lock to lock with the car stopped and the front wheels on a soft surface. That includes putting cardboard pieces under the front wheels so they can turn w/o too much resistance. This can help clean the potentiometer wipers that are difficult/impossible to access.

I guess you are not the only NHW11 driver here who is managing an EMPS issue, so please keep us poted on everything you do.

 

Heh. That's because the air conditioner codes are so easy an expert can't read them. Turn the key and fan switch to off. Turn the key back to ON and within 5 seconds press the AC button 3 times then switch the fan to AUTO. Wait for the lights on all the AC buttons to go through four slow flashes, then read the blink codes from the AC button light. If it's just a steady fast blink, there are no codes.

The steering codes are trickier. vincent1449p tried out the Techstream software and found that it can indeed talk to the EMPS. Once we find out the addresses it's using we can do that with a ScanGauge too. Until then, you can still get its codes without a scanner, which is pretty easy if you add a light.

-Chap

 

An observation that can reduce wear on the tires and your arms would be that we only need to work the potentiometers across their full range of travel, which doesn't depend on how far the front wheels move, but only on how hard you're turning the wheel (as long as the key is in and turned so the steering column isn't locked).

If the tires are on hard pavement so they won't turn easily, the EMPS motor is unplugged so it won't assist you, and you unlock the steering and just lean pretty hard back and forth on the steering wheel without moving the wheels much, you will be working the potentiometers back and forth. If you're measuring the VT1/VT2 signals you can see if you're getting the full range of travel: if you're swinging the voltages between 0.5 and 4.5 volts, you're leaning hard enough.

When vincent1449p tested the Techstream software he saw that the EMPS ecu has parameters for directly reading the VT1/VT2 voltages on the scanner. Can't wait till we work out those addresses for the scangauge. Much tidier than trying to stick voltmeter probes on the VT1/VT2 pins.

-Chap

 

I agree with Chap, the way to exercise the pots is to get the road wheels ad the steering wheels 'out of phase'. Get some torque build up in the torque plate. How to do it best is hard to specify. If the front wheels are off the ground (use very safe jackstands) and outside person pushes the wheels towards "left turn". While steering-wheel person makes a right turn. Something along those lines.

But really I think that any such efforts can only be temporary. THis design turned out to be a loser for Toyota and they fixed it by later using Hall Effect sensors instead of potentiometers.

For manual steering, when you are in that mode, the weight of the car is not the only factor for steering force. Cars initially designed to be manual steering have lots of steering wheel turns 'lock to lock'. Steering-assist designs like Prius have few turns. Mechanical advantage.

 

The appeal of watching the torque signal voltage is that you can tell how much trouble is enough. I think as long as you're sitting in the car, wheels on the ground, steering unlocked, and wiggling the wheel back and forth hard enough to repeatedly see 0.5 V and 4.5 V, you're doing all you need to or can do.

Naturally ignore any quick voltage spikes you see while moving the wheel, since we're doing this because we already know the pots are noisy - you're looking for the 0.5 V you can hold steady in one direction of wheel rotation, and the 4.5 V you can hold steady in the other. Then just remember what that felt like and wiggle the wheel back and forth that hard until you get bored, and see if it drives any better.

-Chap