Mass Air Flow (MAF) Sensor Resistance Measurement

Discussion in '80-Series Tech' started by LXCRSR, Jan 1, 2012.

  1. LXCRSR

    LXCRSR

    Messages:
    355
    Location:
    Lehi, UT
    While trying to trouble shoot an issue, I came to the point where I needed to check the resistance of the MAF sensor between the THA and E2 terminals.

    If I check using my multimeter (Fluke 8062A) in standard ohm measurement mode, I get a reading of non-continuity.

    However, if I check the same terminals using the auto-ranging ohm measurement mode, the resistance reading is within specifications.

    I have validated these results with a second multimeter.

    From reading the manual with my multimeter, the only difference I can see between the two modes is that the auto-ranging mode uses "enough voltage to turn on semiconductor junctions." While the standard mode does not.

    However, in looking at the electrical schematic in the FSM, it does not appear that a junction is present that needs to be turned on, so I am uncertain about this result.

    Can anyone tell me which reading I should rely on as a test result?

    Thanks,

    Tom
  2. landtank

    landtank SILVER Star

    Messages:
    17,177
    Location:
    Groveland MA
    typically when in standard mode you need to select the range the for the meter to use. If the range is too small for the resistance you are reading you will get an infinite reading. Auto ranging does that for you. If the reading from the auto range setting is OK then the sensor should be fine.
  3. LXCRSR

    LXCRSR

    Messages:
    355
    Location:
    Lehi, UT
    Rick,

    The FSM says the resistance should be 2 -3 kohms at 68 degrees F.

    If I put my multimeter in the 2 kohm standard mode, I get non-continuity.

    However, if i put it in the auto-ranging mode, I get a reading of 2.65 kohms.

    This is why I am confused on which reading to believe. I would think that in the standard 2 kohm mode I would be able to get a reading if the resistance really is 2.65 kohms.
  4. landtank

    landtank SILVER Star

    Messages:
    17,177
    Location:
    Groveland MA
    I'm not familiar with your particular meter but I think the 2 kohm scale is too small of a range to read the resistance of 2.65 kohms.

    If the reading is within range in the auto mode it is fine.
  5. LXCRSR

    LXCRSR

    Messages:
    355
    Location:
    Lehi, UT
    Rick,

    You were right. When I set the meter in standard mode at 20 kohm I got a reading of 2.65 kohm.

    Thanks for helping me figure out how to use my multimeter:cheers:

    Tom
  6. george_tlc

    george_tlc SILVER Star

    Messages:
    1,850
    Location:
    Sunnyvale, CA
    Yes, with your meter on the 2k ohm range, any value larger than 2k would show as infinite/open circuit, since it is larger than 2k ohms. It is THE way that a manually set meter will work. Nothing unexpected and perfectly normal.

    The correct way to use such a meter (for an unknown resistance) is to set it on the highest range first, if it displays insufficient resolution then move down to the next lower range, i.e. approach the reading from above versus below.

    Auto ranging meters essentially do those steps for you, what they trade off is that it takes a little longer to get to the best range - which is why most good ones provide a way to lock out the auto ranging and allow the user to set the range they want to use manually. Of course that presumes the user knows what they're doing :)

    cheers,
    george.
  7. LXCRSR

    LXCRSR

    Messages:
    355
    Location:
    Lehi, UT
    George,

    Thanks for the sharing your knowledge.

    The user is learning and appreciates the help!

    Tom

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