Violent steering wheel shudder, lights go out, oh dear!

The main thing that a lot of these symtoms have in common is things (like the power steering) that are controlled by computers, and computers being rather finicky about their power supply voltage, and just turning the heat up full blast (which may have turned on some electric elements for supplemental heat, which added another heavy electrical load). How old is the small 12 volt battery in the cargo area?

If it were me I might see if I could get it to do that again, maybe with a minimum-reading voltmeter hooked up to see how low the 12 volts dipped at the moment you put the full-blast heat on. Back at the battery might be one place to make that measurement, and up at the power connection of the steering ECU might be another.

Did the dealer tell you any diagnostic codes they read out? Surely that incident would have set some codes....

-Chap

 

The cabin heater core (heated via engine coolant) is supplemented by two little electric heaters. When you require max heat, the electric heaters will come on and they require significant current. My guess is that you had your headlights on and the rear hatch defroster as well, which also consume substantial power.

The electric power steering system depends upon the constant flow of 12V current. Apparently all of that load on the electrical system was sufficient to shut down the vehicle. I wonder if your 12V battery is marginal, so that it can't supplement the DC/DC converter under peak load situations.

If you want to test your car's electrical system, make the car READY, then try turning on every electrical accessory, including cabin heat to max temp and highest fan speed, rear defroster, all lights, then see if your car has a problem. If not, take it for a drive and see if the problem recurs or not.

If the problem comes back, my guess would be that the DC/DC converter within the inverter has a problem so that it cannot output its rated maximum current.

 

Jeez, why didn't the dealer use a voltmeter to check the 12V battery voltage, with the car both OFF and ON? If you have a voltmeter you might do that yourself at the jump points under the hood and tell us what you find.

And why did the dealer bill you? Is the car past 36K miles? If not, then this all should have been warranty work at no charge to you.

 

Indeed if luna has less than 36k miles a steering torque sensor recalibration (and almost all other things) should be fixed for free.

I agree that we need to know that the 12 volt system is healthy before considering problems in the steering system itself. In the earlier Prius it was susceptible to several problems, but the new model is changed in important ways.

To the earlier discussion of 12 volt power loads, I will add that the steering electrical motor will draw a lot of current if it is comanded to do so by the PS computer.

Talking to Toyota probably meant that they wanted to know if steering shudder was at all common in the new model.

Please let us know what you find out next.

 

Hi All,

This sounds like the connections to the 12V battery in the wheel well have either come looser, or were never tightened properly. The battery is shipped along with the car, but not installed. This is done by the delivery tech. This has been reportedly a problem for other people on PC here.

If the battery clamps were loose, then the heater load would result in excessive voltage drop due to the high resistance of the loose battery clamps. This would then drop the supply voltage to the computer modules to below the usual 9 Volt regulator minimum acceptable input voltage. And allot of the sensors would start to give eroneous readings, or the analog sensor interface stuff would start to not work right.

Now people have actually started a Prius, and disconnected the 12 V battery and it kept running. I am not sure if these guys actually drove the car around int he winter, though.

One has to think that battery is there to provide a low power supply source impedance too. And loose connections would increase the power supply source impedance considerably.

 

Measure the 12 volt boot battery they are all talking about. Easiest way is to measure it under the hood with a DC Voltmeter. Open the black plastic box on the right under the hood by pushing in the bottom edge along the top of the box which releases the 2 clips and then the cover pulls right off. You'll see a big red plastic cover top left. Swing that cover open revealing a bolt. That's the battery positive terminal. In OFF that terminal on my perfect running 2007 measures to ground 12.8 volts. When car is in READY it reads 14 volts.
Good place to start.

 

Hi Ed,

Its hard to replicate the electrical oad of a specific driving situation, especially when the power steering is involved. The car may have been resisting a turning force presented to the wheels due to a roadway defect. Which would put a large current demand on the system.

Best thing is to go back into the wheel well and physically evaluate the battery clamps directly. I think this has to be done before moving to any other possibilities.

 

Two things that I only know for sure about the 2001-2003, but might also apply to a later Prius:

1. If you are the sort of person who for some reason considers it geeky to own a voltmeter, there is also a mode of the MFD that should show the aux battery voltage. I think you have to be stopped with the parking brake on before the MFD will go into that mode; what I don't know is whether you can then drive off and let your passenger watch the voltage.

2. The DC/DC converter has (at least in the 01-03) and output signal (IDH in the wiring diagram) to the heater controller, which allows the converter to say "hey, I'm under a lot of load right now, could you shed the electric heat for a sec?". This is probably a less likely issue than some problem with battery condition or battery clamps, but I guess if there were some problem with this signal circuit it could result in the heater not shedding the extra load when the converter wants it to, and exceeding the load capacity.

Who knows, in the 2004- that might be a CANBUS message instead of a separate wired signal.

-Chap

 

As a former owner of a 2002 MY Prius, you have just experienced the "death shudder". Don't assume that turning on the heat had anything to do with the problem. It could be that you just moved the steering wheel just a little to the left or right as you messed with the heater control. When the steering goes into one of these uncontrolled oscillations, the steering wheel can be literally ripped out of you hand. The whole dash will shake like crazy. Just wait till it happens while you are turning left thru oncoming traffic (been there done that). When I took my Prius to the dealership to diagnose, they were skeptical until it did the death shudder while the service writer was moving the vehicle. I got the whole steering gear replaced - worked great after that.

 

Hi Dick,

Sorry about your death shudder, glad you got the steering gear replaced.

The original poster here said the car was a 2007. From 2004 MY on, they used a new rack design with a Hall effect sensor instead of the mechanical resistive sensor in the 2001-03. I would not rush to the conclusion that this problem was the steering rack death shudder associated with the earlier rack design. Other indications that the problem was more systemic were that the dash lights went out, and the range selector went to neutral. A dip in the 12-volt supply common to those various systems might explain what was seen.

-Chap

 

Just for our information, how do you go about turning on the heat?

Tom

 

The key item here is pressing HIGH. That would have caused the electrical resistance heaters to come on line, adding a bit of a load to the electrical system.

Tom

 

From 2004 MY on, they used a new rack design with a Hall effect sensor instead of the mechanical resistive sensor in the 2001-03.

-Chap[/QUOTE]

I am one of many owners of the 2001 Prius who have experienced the steering wheel death shudder. With just 117 K miles on my Prius, I have discovered that my vehicle has NO trade-in value with my dealer (even though I faithfully maintained it according to schedule with them) because of the steering rack design flaw. (Have you ever known a car salesman to not call you back when you ask him to give you a quote on the trade in value of your car?)

So here is my question: do I go ahead and pay $2K for the new steering rack and hope the battery lasts for another 35K, keep driving the car until the steering rack malfunction kills me, or dump the worthless piece of junk and never buy a Toyota again?

 

Any design which allows the steering to be affected by a transitory low voltage condition doesn't seem terribly well thought out to me.

And the death shudder is especially troubling; steering is one of those things which should never fail suddenly.

I can't lie, as much as I love the idea of the Prius, sometimes it seems a bit too complicated for its own good.

 

The Gen2 Prius power steering does NOT use a hall-effect system for torque sensing, it uses a Rotary Variable Differential Transformer (RVDT). It will not fail like the Gen1 system that used a mechanical potentiometer.

This does sound like a simple low-voltage problem that could have indeed been caused by a faulty relay, a bad 12v battery, a bad connection, or a fault in the DC/DC converter. (though the latter would normally set DTC's to this effect.)

Normally the power steering will go offline when the voltage drops too low, but an oscillation caused by a bad connection could cause a shudder.

I would try to reproduce the problem by intentionally turning on as much electrical load as possible. All heaters (defrosters/mirrors), high blower, high-beams, fog lights (if equipped), run the steering back and forth all the way, and even play with the windows. If you can cause this to happen again, then it wasn't the relay.

As donee pointed out, a simple one could be loose or corroded connections on the 12v battery. Also the health of this battery should be checked. On a cold day they loose a lot of capacity, and the DC/DC converter is not temperature compensated, so it will never fully charge it when cold.