Power steering ECU question

Discussion in 'Generation 1 Prius Discussion' started by depriusoto, Jul 20, 2014.

  1. depriusoto

    depriusoto Member

    Jul 23, 2007
    Albuquerque, NM
    2002 Prius
    I was recently driving my niece's 2002 with 143,500 while she was out of the country for a month. Twice with a week (on two separate occasions0 the car through the triangle of death and the PS warning light on the screen and the steering got hard. The first time, I pulled over and stopped and checked my scan gauge II for codes - it showed none. At that point I looked back at the dashboard and the warning signs were gone. Put the car in D and pulled back on the road and drove on with no problems. A few days later, the same thing happened and as I was looking for a safe place to pull over, the warning lights again disappeared and this time I saw the message on the screen, "Problem has fixed itself". I didn't check the Scan Gauge since I'd remembered it doesn't track PS codes.
    It is now about a week later and my niece is coming back home. I hooked up my AutoEnginuity and it showed these codes:

    C1521 short in motor circuit control

    C1533 power supply sensor

    C1551 ig power supply voltage mal function

    NOTE When we bought this car in February of last year and had it checked out by Jim's Automotive here in Albuquerque, they found PS codes stored and cleared them. So far as I know, my niece has had no problems this last 17 months, but I will ask her after she gets over her jet lag. I'll be checking back with Jim's tomorrow to verify what codes they pulled to see if they are the same ones.

    Looking at my 2002 Prius shop manual I found that all three of these codes have one thing in common,
    the EMPS ECU. When I search here I found this old thread from 2010

    used steering rack installed -- now dealer says it needs ECU | PriusChat

    I'm thinking that the ECU is the culprit and that replacing it would solve the problem (if it gets worse!). A bit of research turned up the fact that there were 3 different part numbers for this unit and that they were all superceded by 89650 47190. That part is available on EBay for less than $100 bucks (as are the ECUs that were superceded) which is a lot less then $600 new from Toyota. I will also check locally.

    In the thread from 2010, Bob Wilson, you were going to look into this ECU but that thread just kinda of ends and I don't know what you found. Can anyone point me to newer thread(s) that show your results?

    Long and short of it is, have those of you who got similar codes found that replacing the ECU solved the problem?

    Ed K in Albuquerque
  2. ChapmanF

    ChapmanF Senior Member

    Mar 30, 2008
    Indiana, USA
    2010 Prius
    Something like this usually splits into two cases: (1) the problems the ECU is reporting really exist (for example, there's a short in the motor wiring, or a problem in the IG wiring that supplies the ECU), in other words, the ECU is telling the truth; (2) those problems don't really exist outside the ECU itself, and it has gone faulty causing it to report those codes.

    In case (2), replacing the ECU should solve the problem. In case (1), the replacement ECU is likely to detect the same problems and report the same codes, and those original problems will have to be tracked down and fixed.

    Looking up those codes in Volume 1 of the shop manual will lead to a tree of things to check for each code, that Toyota regarded as the most efficient way to pin down whether it's case 1 or case 2. For example, it will give some steps to check for shorted wiring, but if the wiring checks out ok, it will suggest replacing the ECU.