2002 Prius loses power steering occasionally - no vibration

Then y not just try getting a used steering rack and pinion that you're sure of?

 

Then check it out and confirm.

 

What are you referring to here? There is no steering fluid.

It can happen either way. When the torque sensor is (electrically) noisy, whether you get the wet-dog-shake or not interestingly depends on how you habitually hold the wheel. (The shake is an oscillation in an active feedback system, and the mass of your arms, and how loosely or firmly you hold the wheel, is all part of the system.)

C1513 is a torque sensor code. If you had a data recorder on the torque sensor VT1 and VT2 outputs, you might see something like this, where I had the red pen on VT1 and the black pen on VT2. Notice they are supposed to be mirror images of each other (accounting for the two pens having to physically be a few mm apart), but occasionally the black VT2 trace takes a quick dive over to the wrong (same as VT1) side. (The solid colored-in spots are where I managed to catch shake events; those were extra entertaining with the pen recorder.)



Now, those wire harness connectors are part of the torque sensor circuit, so if they were bad once, you could luck out and have them be bad again. They're devilish hard to reach. You might be able to reach them from above after removing the cowl, if your arms are longer and bendier than mine, or from below if you have a way to lift the car. They may defy you unless you actually lower the subframe some. If you look at the PDF for the pinion nut service campaign, it has some very interesting notes on protection of the subframe when lowering.

On the other hand, at the age of your car, it wouldn't be surprising at all for the torque sensor to need some love.

I did, at one point, give in and buy a cheap used rack just to figure out how to open up the torque sensor. I've had quite good results just using a swab and Jiffy Bath on other potentiometer-based sensors in the Gen 1 when they get flaky, and I would not be at all surprised if it worked for the steering sensor too. I don't know if anyone has tried since I posted the teardown steps. The main obstacle, of course, is the labor; you don't save any steps over just replacing the rack.



On the other hand, if you know your rack is sound and has had the pinion nut done, maybe cleaning it up is less of a gamble than shelling out for a used one. Or, you could get a cheap used one, and clean up the sensor first before doing the swap. You would even be able to check if it's had the nut done (the new nuts are visibly different, as the PDF shows).

-Chap

 

Replacing the steering rack is a half-day job, if you have all the tools and patience. I speak from experience. Bracing the car (if it is not on a body lift) is a bit tricky. But steering is a system that you do NOT want to have fail at 100 km/h.

RockAuto has (ACDELCO 36R0921 {#19321019} Professional; Remanufactured ) 2001-2-3 steering assembly for US$710.79 plus $150 core charge, US$860.79 total. Having looked at the one I took out (the steering casing had cracked, after 180k km), the labor economics of doing the job had me put in a completely remanufactured part rather than try to repair the old one.

As Chap said (above), the torque sensors are devilishly hard to reach, and I might add, it is unlikely that spares would be available at any local parts store. Whatever your decision, I wish you good fortune.

 

To be clear, my "devilish hard" comment above was just about the two external wire harness connectors to the rack (which are clipped to a bracket on the rear of the transaxle making them just about equally defiant to reaching from above or below).

I'm not saying the sensor itself is easy to reach! You have to get the rack out, and the top bearing cap off, so "devilish hard" would be apt there too. But at this point, I suspect any satisfactory fix is going to involve getting the rack out, so that half-day's labor is a given, and then it's just choices what to do then.

-Chap

 

I have the same situation on the 2002 that I'm buying back from my niece. It has 156K miles and this has been a reoccurring problem since she bought it on 2013.

NOTE: WHEN i picked up the car and drove it home it drove fine. (No Triangle of Death and No PS warnings)

When I got it back from her and put it on my Techstream I found these stored codes:

C1522, C1523 Motor Circuit Malfunction defined as (pDI-481 in Vol1 of the 02 Shop Manual) Short circuit of motor terminal or abnormal voltage or current in motor circuit.
Trouble area is1) 'Power steering gear assembly with motor" and/or 2) EMPS ECU.

C1551 IG Power source Circuit Malfunction defined as (pD-I487 in Vol1 of the 02 Shop Manual) "the abnormal IG voltage value which which is not within the specification is input to EMPS ECU.
Trouble area is 1) EMPS ECU 2) Power source circuit 3) Charging system.

Using Techstream I cleared the codes and then ran the Test Mode which generated the
C1571/1572 Speed Sensor Malfunction (Test Mode).
Trouble Area is 1) right rear or left rear speed sensor 2) sensor installation 3) Right rear or left rear speed sensor rotor 4) Right rear or left rear speed sensor circuit 5) Brake ECU 6) EMPS ECU.After restarting a couple of times these codes were gone.

A couple of days later when I started the car and after I backed out of the driveway, when I went forward I experienced the no-PS driving (like driving 42 DeSoto!) but it left no codes and disappeared when I restarted after driving 1/2 of mile. Drove back from the car wash, turned the car off, then restarted and -yup- no PS was back this time with dash warning. Drove to the car wash, washed the car. Started up and it was back to normal. PS and no warning signs. Drove home. put it on the Techstream and no stored codes...

I'm planning this weekend to run the tests outlined in the Shop manual to ID the problem. At this point I'm leaning towards the good possibility that it is a loose/corroded connection in the power source into the EMPS ECU. The interesting hint to this is that while I was running the Freeze Frame Data gathering program for EMPS I got these error messages that power was lost. I was directed to check to see if the ignition was on (yes) and the data cable was plugged in (yes) or the power source was connected. When I'd opt to retry, sometimes it would reconnect other times it didn't. I also noted that when I ran the Freeze Frame Data gathering program for the Cruise Control or HV Battery, etc. I didn't get these error messages. So I suspect a power in problem. Also, I'll be looking for a short or open circuit to the EMPS ECU.

There are a couple of tests for the EMPS ECU to determine if it is working correctly. Has anyone had success with these in identifying a shot EMPS ECU? My research as shown there are a number of used ECUs from salvage yards on EBAY -these having either these part numbers: 2001 (89650-47050, 89650-47051), 2001/2002 (89650-47070) and 2002/2003 (89650-47071) or the super-ceded replacement (89650-47190). I also found a company that re-manufactures the ECU (What does that entail???) and a couple of on-line Toyota part suppliers who still have the OEM super-ceded replacement (89650-47190) - discontinued by Toyota so not stocked by most of the dealers.
The Ebay parts are used and under $100 mostly. The re-manufactured was around $400 and the new OEM was between $600 and $#700.

Anyone has experience swapping out these ECUs you can share?

THanks,
Ed K

 

Good troubleshooting tale. Rather than a defective component, I would suspect (as you did) an intermittent connection to the ECU. My next investment would be a can of good contact cleaner, and examine/clean all the connections I can find along the PS steering path. Next is to examine the speed sensors on all four wheels, to see if they are damaged or (again, my favorite hypothesis) one of them has a grotty connector pin. If the ECU were defective, you would get a consistent error all the time, so you are likely looking for something that comes-and-goes... if you do choose the replace-the-ECU route, I am currently parts-ing out a 2002 Prius, and the PS ECU is available. I'll look at the part number tomorrow, and if you're interested, we can chat.

 

Followup. I kept getting the EMPS codes, the power steering would work and then not work, so I did some more checking with TechStream. In the process of reviewing health checks and clearing DTCs, I realized that I had forgotten the number 1 trouble shooting suggestion for GEN 1 owners. Check the 12 volt!. And then check it again.

I had to jump the car a couple of times to get it started when I first bought it. So I pulled the Optima Yellow Top and put it on the charger and got it eventually up to 13.? volts and thought it was good to go. But after Ii put it back in, I kept having the EMPS codes thrown, the EMPS lose power, and when starting the car, the MFD screen would flicker, go black, and flicker. Checked the last health check and it showed the 12volt at 10 volts. Checked the battery in the car a few minutes later after I'd turned off the car and found it had gone back up to 13volts. Pulled the battery and this time, I used my new load tester and, of course, under load the battery was shot.

So, I bought a new Yellowtop and installed it last Saturday. So far no more EMPS codes, so I'm cautiously optimistic it was just a near dead 12volt causing all the codes.

SO here's my next question. In an earlier time, when working on my old VW bus, I had learned that if, when I attached the negative ground cable to the battery post and it sparked, that meant there was a short somewhere.

When I attached the new battery in the 02 - that's what happened. Sparks at the ground terminal.
I've done some research here in the Chat and found that there is such a thing as 'parasitic draw' but that it shouldn't be more then 30-50 milliamps. I'm going to test for that tomorrow. I've hunch that there may be, if not a short (that would blow a fuse) at least a current drain somewhere that slowly draws down the 12volt. I won't be surprised it if turns out to be in the EMPS circuits.
Since we can't have fireworks here in Albuquerque due to the extreme fire danger from the prolonged drought, I'll have to settle for messing with electrical circuits for my 4th of July!
I'll let you know what transpires.
Ed k

 

Not to take this too far off the topic of steering issues, but I've read the same mA parasitic draw amount, but everyone who shared that had a newer model. I have seen anything from anybody who owned a Gen 1. Because of that and because of so many improvements with the Gen 2, I take the 30-50mA lightly for a Gen 1.

I measured my 2001 and found ~160-180mA (can't remember the exact number). When I pulled every single fuse and relay from every fuse box, only the DOME 15A fuse changed the current draw, and it's changed it massively.

The DOME fuse however controls the security system, and many many other things. I never troubleshot deeper than that.

Curious of your results and what anybody's done to fix this power steering issue. I don't have it myself. I'm just curious

 

Correction,
For what ever reason, I don't get 160-180mA, but instead get a lower number that slowly drifts down.

Now, 134-138mA
Over ~10 minutes, it's drifted to 131-134mA.

I first measured >40 minutes after the car was off. This may be why it was ~135mA instead of ~170mA that I measured before. It's obvious that every 5-10 minutes, the leakage is slightly lower.

I removed the DOME fuse, to reconfirm what I wrote earlier, and I only saw ~10mA drop. ( I could have sworn this dropped much much more.)
When I returned the 15A DOME fuse, the total current draw was 172-176mA. It then sat like this for ~1-2 minutes, then jumped down to 131-134mA.

So, my correction above, wasn't necessarily a correction, but a clarification.

Fuse voltage drops
HV 20A fuse - ~7mA
DOME 15A fuse - ~10mA (when I first checked it, weeks ago, the timing may have been with the natural drop from 170mA -> 133mA and gave me the impression it made a bigger difference than I thought)
** No other fuses from either fuse box in the engine bay, made any difference in parasitic draw. **

Now back to steering issues and @depriusoto @telenochek 's troubleshooting to fix the power steering drop-off.

 

Hi hoping I can get some help. I get the intermittent PS triangle and when I turn the car off and on it resets and usually no more issues for that trip. Im getting it daily now. So I am want to disconnect the ECU to see if that helps. I thought when I disconnected it that I would not have power steering at all but to the contrary I still have steering unless I disconnected the right box. Its a black box right behind the steering column, and has only 1 connection. If this is not it can someone point me in the right direction. I am also finding the dash incredibly hard to get behind. Thanks.

 

I know I'm necroposting a little bit, and this isn't strictly about the steering, but here goes. Also, ping @LeeD .

John Muir probably taught you that, and it was 100% true for a stock air-cooled VW. Modern cars have more things in them (mostly computers) that need power all the time; this is where you get that "parasitic draw" number of 20 to 50 mA that gets bandied around. Also, the things that want power all the time tend to have a smallish capacitor across the 12 volt input. If you leave the 12 V battery disconnected for a while, these capacitors tend to discharge to some low voltage. A capacitor at 0 volts (or close to 0 volts) "looks like" a dead short when you turn the power back on. When you go to hook the 12 V battery back up, you have to "fill up" all of those capacitors, all over the car, all at once. This causes a relatively high current to flow for a second or so until they're filled up, which is partly why you get the spark you saw.

This happens to some degree in just about any fuel-injected car. The more computers and electronics the car has, the bigger the spark you will get.

I have tested the current draw from the aux battery on my '01 before, and when I first hook up the meter, it shows maybe 1 A for a few seconds. It then steps down to something around 0.1 A for maybe 30 to 60 seconds. After that, it drops off to a lower value, around 0.05 A or less (from memory).

If you've got the trunk open to test this, don't forget to disable the trunk light. I find it's easiest to unclip the whole light fixture from the ceiling of the trunk and then unplug the electrical connector, rather than trying to remove the lamp. If that light is on, it will be good for about 200-250 mA (0.20-0.25 A) of "extra" draw.

 

Gen 1 steering ECU is over at the right end of the dash, behind the glove box. Very easy to reach by dropping the glove box out. Two ECUs are right next to each other, engine and steering. You can recognize the steering one by four extra-thick wires running to it (wires to the steering motor, and wires bringing power for that). You can recognize the engine one by the car not starting if you unhook it by mistake.

-Chap

 

I am having similar issue. Power steering failed occasionally. Now it does not work at all. Does a used power steering ECU need to be flashed after installation?

 

I had this issue on my 2001 Prius. Went thru everything you all have posted here. Found a dead Prius in the junkyard. Pulled the powersteering rack thinking it was bad. The PS rack on this vehicle is well engineered. I disassembled the motor from the rack and broke down the rack further to the internal sensor boards. For a junker, the internals were clean as the day it rolled off the factory floor. The PS motor attached to the rack is heavy duty, like that of a wiper motor, not likely the issue. I then focused on the PS ecu. After removing the ecu from the car and opening the cover I found 4 large power diodes. As an electronics technician having worked on radar systems and semiconductor equipment, I surmised the issue may be caused by a bad power diode in the PS ecu. In my work experience with power supply systems and electronic controls, I know power diodes do fail after a fair amount of time under high current loads. Diodes under the stress of high current voltage loads just get leaky until they fail entirely. I removed and purchased the power steering ecu from the junkyard for$20, plugged it into my car, and my power steering worked like normal again. Hope this helps. I will post photos if I can find them.

 

Willy^3... Great pictures, good analysis! Are the pix of the failed PCB? Did you ever check out your failed diode theory? Would you consider (as a gee, I tried it and it works experiment) finding an appropriate replacement diode and attempting a PCB repair? Unfortunately, Radio Shack is demised (although it is apparently resurrected as an online-only storefront, I just discovered), so it's an online search for the individual part...