Easy Way to Check Voltage Reg. on 98 Civic?

Is there an easy way to check the voltage
regulator on a 98 Civic?

 

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?

Mike

 

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.

 

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.

Mike

 

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.

 

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.

 

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.

Mike

 

AC reading across the battery?

Shorted diode?

If that is the right area, couldn't it be an open diode?

 

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 wrote:

It certainly *could* be an open diode, but most common failure mode for
diodes is to short rather than open.

 

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.

Mike

 

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.

Mike

 

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.

 

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.

 

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...

 

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.

 

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.

Mike

 

Hmm. OK, thanks.