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456 Power Steering Trouble Shooting

Discussion in '456/550/575' started by DrivenHK, Aug 7, 2019.

  1. DrivenHK

    DrivenHK Rookie

    May 1, 2019
    14
    Thank you everyone for your posts.

    Was that bet made on a 456M or 456? Is it a possibility that the 2 ECU versions output to be PWM on one model and DC voltage on the other?

    When cycling ignition switch on/off - there is a momentary voltage reading measuring across the ECU outputs.

    Waiting to borrow a handheld oscilloscope to further confirm.

    Yes, 100% duty condition was the intention. Hopefully didn't burn it out with 12V. Incidentally bench tested the old servotronic with 12V. It didn't react nor did i see any smoke, which led me to believe the unit was bad. How much resistance should be expected across the terminals on a solenoid like this?

    The servotronic (spoolvalve/TC) is a new unit.
    Harness from ECU output to spool valve Continuity test OK.


    I thought as a safety feature should PS ECU or power failure occur, that the spool valve would automatically set itself in a position of min assist (in case failure occurred @ 200kph.) If the opposite were true, then then this car's PS problem is not a software issue.

    Today the harness was unplugged/open circuit and had to move the car. There was a few moments when there was power assist! The pump is new. The rack works mechanically and isn't leaking externally.
    Is it possible an internal seal/rings is bad, allowing high pressure straight back into low pressure or some kind of blockage in the lines?
     
  2. DrivenHK

    DrivenHK Rookie

    May 1, 2019
    14
  3. Cribbj

    Cribbj Formula 3
    Rossa Subscribed

    Jan 1, 2011
    1,985
    Houston
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    John
    It was a 550 steering ECU, but I suspect since your rack has the same Servotronic spool valve as our 550's, then the signals are similar. The ECU's are just packaged differently.

    Didn't realize you'd already replaced the spool valve. This is indeed puzzling. It'll be interesting to see if your measurement of the valve solenoid's resistance is the same as reported on the BMW forum.
     
  4. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
    2,641
    Sydney
    Full Name:
    Ian Riddell
    Did you read further into the message thread on that forum?

     
  5. Cribbj

    Cribbj Formula 3
    Rossa Subscribed

    Jan 1, 2011
    1,985
    Houston
    Full Name:
    John
    DrivenHK, have you made any progress with this?
     

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