Repair Manual HV ground fault tests improved in later editions?

Discussion in 'Gen 2 Prius Technical Discussion' started by ChapmanF, Dec 26, 2019.

  1. ChapmanF

    ChapmanF Senior Member

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    Another thread has identified a bit of an infelicity in the version of the 2006 Repair Manual that one finds circulating on the web (which ISTR @Elektroingenieur has said lacks updates compared to what's currently on TIS).

    Specifically, that troubleshooting sequence has a step 15 to check for "sticking" system main relays, and it has an illustration showing the frame wire completely disconnected at the battery end, not just from the SMR's HV terminals, but also the shielding disconnected from the case. That leads to trouble in step 16, which unplugs the front end of the frame wire from the inverter, leaving no shield-to-body continuity anywhere, and then purports to megger test the cable from the center conductors to body ground. :)

    But there is more about this sticking-relays test that bothers me. It offers a "standard resistance" of less than 1 Ω, between the switched SMR terminals. That would seem to be the result indicating that the relay is sticking. When de-energized and not sticking, I'd expect a result not only above 1 Ω, but probably above n MΩ.

    Usually, the "standard resistance" given in a test step is the result that would indicate passing. Not always: step 14 is a counterexample, where the "standard resistance" is really the result you'd see if some modules were leaking. But step 14 also flops the meanings of OK and NG to match: step 14's "OK" is to replace the battery because of the leaky modules you found, and its "NG" is to replace the ECU because the modules were OK. :)

    But step 15 seems to have an inverted "standard" result without inverting OK/NG to match it. Getting the "standard" result would mean the relay stuck, but they still have you replace it on the NG branch, not the OK one. I think I'd consider that a bug.

    It seems like @Elektroingenieur has fairly convenient access to the updated versions (my TIS subscription is lapsed at the moment) ... any observations on which of these points have been clarified / fixed in later updates?
     
  2. Elektroingenieur

    Elektroingenieur Senior Member

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    You recall correctly. The ease of revision is, of course, one of the major advantages of electronic publications.
    In later editions, the P0AA6 procedure no longer includes tests for sticking relays. There are other stuck relay DTCs, such as P0AA1-231, P0AA1-233, and P0AA4-232; the P0AA1 procedures refer to Engine/Hybrid System: P112 Hybrid Battery Control: System Main Relay: Inspection, and the P0AA4 procedure says to replace the No. 3 System Main Relay without further troubleshooting.

    In the restructured P0AA6 procedure (previously discussed), an “NG” result usually, but not always, leads to replacement of the last part tested.
     
  3. ChapmanF

    ChapmanF Senior Member

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    Good to know. "Usually, but not always" sounds rather like the old version, where step 14 supplied the "not always" part.

    As far as testing the frame wire, does following the sequence still end up with you meggering between the frame wire and body ground after the shielding has been unhooked from body ground at both ends?
     
  4. Elektroingenieur

    Elektroingenieur Senior Member

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    Yes, I think so. With only INF code 526, the test of the frame wire is now done in step 7, with power OFF, the service plug grip removed, and frame wire disconnected from the inverter (from previous steps) and disconnected from the system main relays. The illustration (A087670E01) is the same as in step 20 of the old edition.

    With INF codes 526 and 614, the test of the frame wire is done at the inverter end, with power OFF, the service plug grip removed, and the frame wire disconnected from the inverter, but nothing else disconnected.
     
  5. ChapmanF

    ChapmanF Senior Member

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    Hmm ... I guess I'd still call step 7 a bug ... unless it simply says to meg between the center conductor and shield rather than body ground. Sounds like the 614 case ought to work now.
     
  6. Elektroingenieur

    Elektroingenieur Senior Member

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    I’m inclined to agree, since the procedure still says, “Using a megohmmeter set to 500 V, measure the insulation resistance between the frame wire and the body ground.”

    For third- and fourth-generation cars, the procedures are better; they call for tests between terminals of the frame wire (called the HV floor under wire on later models) and “Body ground and shield ground.”
     
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