Easy Way to Check Voltage Reg. on 98 Civic?

Discussion in 'Civic' started by Al, Jan 3, 2005.

  1. Al

    Al Guest

    Is there an easy way to check the voltage
    regulator on a 98 Civic?
    Al, Jan 3, 2005
  2. You need to check the voltage across the battery with the engine running. A
    digital voltmeter, even the cheapest one, is the best way.

    The voltage should be between 13 and 15 volts DC, higher voltages in the
    range with lower temperatures. Also measure the AC voltage across the
    battery - it should be less than 0.1 VAC. If it is over 1/2 volt AC, you can
    be sure the alternator has bad diodes. If the regulator is bad but the
    alternator is working, the voltage will be much too high or much too low. 17
    volts DC is a typical regulator failure voltage, and that will quickly
    destroy the battery.

    Are you having problems with the battery not staying charged?

    Michael Pardee, Jan 5, 2005
  3. Al

    Randolph Guest

    In addition to Michael's suggestions:

    The nominal voltage is 14.5 volts under normal circumstances. Factory
    manual allows up to 15.1 volts. In my experience voltage regulators are
    very accurate, +/- 0.1 volts is what I have seen.

    Some Honda's use a system where the set-point for the voltage regulator
    is reduced at idle. On mine (94 Civic), stepping on the brakes will
    defeat this reduction.

    To better asses the health of your voltage regulator you should measure
    the voltage pr. Michael's instructions while you gradually increasing
    the engine RPM. The voltage should stabilize as you get a little above
    idle, and it should never exceed 15.1 volts. I usually go up to about
    3000 RPM, and if the voltage is still steady, I am happy.

    According to factory manual, if you reach 18 volts, abort the test, as
    excess voltage can damage electronic components in the car.
    Randolph, Jan 5, 2005
  4. The voltage is compensated to match the battery's response to temperature.
    In Phoenix warmed up cars in the summer can read as low as 13.2 V. Here in
    Flagstaff the locals tell me the winter voltage can get close to 16 volts,
    but I've never seen it above 15 in anything. My '85 Volvo has a temperature
    sensor mat the battery sits on that connects to the (built-in regulator in
    the) alternator.

    Michael Pardee, Jan 5, 2005
  5. Al

    Al Guest

    No. It's just a hunch and probably wrong.

    I bought the car new. About a year later the air bag
    SRS? light went on. I took it to the dealer. They fiddled
    with it, couldn't find anything wrong, reset the light and
    sent me away. About a week later, the light came back on.
    I went to the dealer and went through the same process and the
    light came back on a few days later. Since
    I didn't plan on having an accident, I ignored the light.

    About 6 months after that, the check engine light came on. Eventually
    ignored that, too.

    The one thing I have noticed is that if you release the accelerator
    from whatever constant speed, the lights - and particularly the
    check engine indicator - dim while the engine is slowing and, I'm
    fairly certain, the SRS light and check engine light were triggered
    while the engine was either at idle or slowing to idle.

    I just wondered if the system voltage dropped to a level that
    might cause these faults to trigger? Just a wild guess.
    Al, Jan 6, 2005
  6. Al

    Doug McCrary Guest

    Radio Shack used to carry a lighter plug-in battery checker that gave some
    of that info. The they had last I checked has five levels and two "ranges"
    for running and engine-off. You have to rig it for a cig lighter or else
    manually connect it somewhere. The only thing it doesn't explicitly do is
    check the ripple (AC), but you can usually see that as rapid flashing of two
    voltage levels.
    Doug McCrary, Jan 6, 2005
  7. Sounds like a possible alternator (not regulator) problem, all right. The
    most common defect of this sort is bad diodes, and an AC voltage reading
    across the battery at idle will tell the story on that. If the alternator is
    bad, forget about the rebuilts from auto stores - they have earned a very
    bad reputation for frequent failure. The stores may offer a lifetime
    warranty, but they won't pay the labor to have it replaced.

    Michael Pardee, Jan 6, 2005
  8. Al

    Al Guest

    AC reading across the battery?

    Shorted diode?

    If that is the right area, couldn't it be an open diode?
    Al, Jan 6, 2005
  9. Al

    Al Guest

    And, wouldn't there be a code for this?

    How do you get the codes out of it, anyway?
    Why didn't the dealer find a code? He wouldn't accidentally
    overlook it, would he?
    Al, Jan 6, 2005
  10. Al

    Randolph Guest

    Al wrote:

    It certainly *could* be an open diode, but most common failure mode for
    diodes is to short rather than open.
    Randolph, Jan 6, 2005
  11. Alternator problems don't set codes - at least, not directly. The OBD II
    codes our cars set are from emissions-related problems. Coincidentally, some
    of those involve signals the engine needs to run. Also for that reason, when
    the "check engine" light comes on it is always safe to continue driving
    around town, or gently on the freeway, as long as the engine seems to be
    running okay.

    Michael Pardee, Jan 7, 2005
  12. The reason for that is the basic failure mode of diodes is for the PN
    junction to "melt" (actually to weaken under heat to the point the reverse
    voltage can break the junction down). Opens occur when the leads to the
    semiconductor break or burn open, like a fuse.

    Michael Pardee, Jan 7, 2005
  13. Al

    Randolph Guest

    Michael Pardee wrote:

    I know some cars have voltage regulators with battery temperature sense
    (Motorola makes chips for this), but I don't think this is the case with
    the 98 Civic. The factory manual gives a hard limit of 15.1 volts in
    their charging system troubleshooting flow chart.
    Randolph, Jan 7, 2005
  14. Al

    Randolph Guest

    Al wrote:

    On my '94 Civic, the ECU will force the voltage regulator to drop the
    voltage under certain circumstances. Specifically, if all of the
    following are true:

    Electrical load less than 10 A
    Vehicle speed less than 40 mph
    Engine speed less than 3600 RPM
    Coolant temperature above 140°F
    A/C turned off
    Intake air temperature above 68°F
    Brake pedal not depressed
    Fuel cut-off not in effect

    then the voltage regulator set point will be dropped from 14.5 volts to
    12.5 volts. This does not mean that system voltage will drop to 12.5
    volts, system voltage will be whatever the battery is supplying, and the
    alternator will not contribute unless the voltage drops below 12.5
    volts. I did not find any description of this in the '96 - '00 service
    manual that I found on-line. Perhaps the feature was not used those
    years, perhaps the service manual is for markets where the feature was
    not used.

    There are several gadgets available that will plug into the lighter
    socket and measure the voltage. Whit the car running, such a measurement
    will not be very accurate, as there may be significant voltage drops in
    the cabling between the battery and the lighter socket.
    Randolph, Jan 7, 2005
  15. Al

    Doug McCrary Guest

    Voltage drop from what? Usually the lighter is on its own fuse straight from
    the battery, no?
    The RS unit I have only draws about 20mills...
    Doug McCrary, Jan 8, 2005
  16. Al

    Randolph Guest

    The lighter plug in '96 - '00 Civics is connected to the ACC output from
    the ignition switch, as is the stereo. There is a single wire between
    the under-hood fuse box and the ignition switch. So the cigarette
    lighter shares this wire with pretty much everything that is powered
    through the ignition switch (emphasis on "powered through", a number of
    the high current systems that are *switched* through the ignition switch
    have relays so that power does not come through the ignition switch,
    only current for the relay coil). The ground lead for the lighter plug
    is also shared with a number of other devices.
    Randolph, Jan 8, 2005
  17. The lighter feed isn't straight from the battery; it shares the fuse box to
    battery wiring with a lot of potentially high draw equipment. The
    uncalibrated voltmeter in my Volvo drops a lot when I turn on the lights and
    fan, even though the battery voltage doesn't waver. Even things you never
    think about, like stereo amplifiers or O2 sensor heaters, can draw enough to
    skew the reading several tenths of a volt.

    Michael Pardee, Jan 8, 2005
  18. Al

    Doug McCrary Guest

    Hmm. OK, thanks.
    Doug McCrary, Jan 10, 2005
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