Honda Accord LX alternator intermittent - ECU or Alternator?

1991 Honda Accord LX, 2200cc engine, 4 door sedan with standard
transmission.

The charge light came on one day, went on and off again, finally came
on and stayed on.

Frustrating... after checking all the wiring, removing and retightening
the battery cables and the wires on the alternator, checking ground,
the light went out. Thought I'd fixed it. In the time it took to pack
up all my tools, went back and started it and the light was on again.

Removed the alternator and battery and had them tested at the local
parts store. Both test good.

Rechecked everything, I see on the wiring diagram there are a couple of
wires that go to the Engine Control Unit/Module, so I take the ECU out
and clean it's connectors by taking them off and on again a few times.
Charge light goes out again. I shut off the car and restart 3 times
(letting it sit a few minutes between), light goes out immediately when
engine starts as it has when things were fine.

Nope, restart car about 10 minutes later and the charge light is on
again. No wiggling of wires or tapping on anything makes it change.

I even took out the ECU and resoldered all questionable solder joints
(I've been an electronics tech for a number of years). Charge light
still on.

During one of the times when it was working, I took some readings. I
doin't know how meaningful they are except they tell me that it is not
a wiring problem between the alternator and the battery.

The only difference between charging and not, one of the two wires
between the ECU and alternator: normal operation, when first started it
is about 3.6V, dropping to about 2.5V. Later starting it and the charge
light comes on, the same line is now about 1.5V.

But without knowing which way this signal goes, I don't know if the
fault is the alternator or the ECU telling it the wrong thing.

I see some mentions here of worn out brushes. Where might I find those
in the northwest USA? I've checked a few places like Autozone and it
lists them but says unavailable.

Thanks,
Steve

 

How many miles are on this 91 Accord LX?

Like you are thinking, and from my reading, I would change
the brush assemblies next. I understand a life of around
100k miles is good for brushes.

You can buy a brush assembly for about $21+ about $7 for
shipping at www.slhonda.com . Click on "Parts and Service,"
then "Buy Parts Online." They're on the West Coast. The
alternator is under the "Engine" section. I have used them
several times. They give good service and have competitive
prices. Add a few oil filters or other maintenance items to
milk the shipping charge for every drop.

Consider changing out the two bearings, for another $35
total or so, too. Though I think the brushes are the first
thing to suspect.

Unless the car's been in a flood, then based on reports here
I would not suspect the ECU. The brushes or maybe bearings
are much more likely to be the problem.

Stay tuned because people have said the brushes are easily
purchased locally at electrical shops. But I don't think
this is the same as the "brush assembly" you'll see at Honda
OEM parts sites.

I am looking to do this as preventive maintenance in the
next year or so.

My 91 Civic's alternator died after eight years and 106k
miles. I didn't know any better and took it to the dealer.
It may have only needed new brushes.

Updates are welcome.

 

How many miles are on this 91 Accord LX?

Like you are thinking, and from my reading, I would change
the brush assemblies next. I understand a life of around
100k miles is good for brushes.

You can buy a brush assembly for about $21+ about $7 for
shipping at www.slhonda.com . Click on "Parts and Service,"
then "Buy Parts Online." They're on the West Coast. The
alternator is under the "Engine" section. I have used them
several times. They give good service and have competitive
prices. Add a few oil filters or other maintenance items to
milk the shipping charge for every drop.

Consider changing out the two bearings, for another $35
total or so, too. Though I think the brushes are the first
thing to suspect.

Unless the car's been in a flood, then based on reports here
I would not suspect the ECU. The brushes or maybe bearings
are much more likely to be the problem.

Stay tuned because people have said the brushes are easily
purchased locally at electrical shops. But I don't think
this is the same as the "brush assembly" you'll see at Honda
OEM parts sites.

I am looking to do this as preventive maintenance in the
next year or so.

My 91 Civic's alternator died after eight years and 106k
miles. I didn't know any better and took it to the dealer.
It may have only needed new brushes.

Updates are welcome.

 

have em run it on the tester for at least 10 minutes. youve covered
every other single possibility, (including a couple id never even
consider like redoing the ECU solder joints!) so id bet on the
alternator being flaky after it warms up.

especially if its 16 years old.

 

have em run it on the tester for at least 10 minutes. youve covered
every other single possibility, (including a couple id never even
consider like redoing the ECU solder joints!) so id bet on the
alternator being flaky after it warms up.

especially if its 16 years old.

 

I would guess that the brush set in your alternator is at the end of
the service life. As a brush gets so short that it cannot make
constant and continuous contact with the commutator (or whatever they
call the rotating contact surface in an alternator), it will give an
intermittant failure signal. often times you can tap the alternator
and temporarily reseat. Therefore the good reading when the
alternator was fooled with to test.

Change the brush set or change the alternator if other things wrong
(bearings)

 

I'm joining the chorus for the alternator. Looking at the Helm manual, the
alternator internals are not the classic arrangement, where generated
voltage from the windings are used to self-excite the regulator and the
light is in series with the regulator supply from the ignition switch. In
those, brush failure is silent - the light doesn't go on because the
regulator doesn't draw current to feed the field through the brushes.

If the manual is right, the light is a warning light from the regulator and
comes on when the regulator can't (or doesn't believe it can) set the
alternator voltage correctly. That covers quite a bit of ground. The ECM
appears to come into play only through the "FR" lead - your guess is as good
as mine what that is, but my guess is that it is a "fault/regulator"
indication to the ECM.

You can troubleshoot in the car when the light is on with a DVM; the voltage
should be a shade under 15 volts DC (depending on just how cold it is under
the hood) and the AC voltage should be under 0.1 VDC. If the DC is above 16
volts or the AC is in the half volt range or above, the regulator or diodes
are bad respectively. If the AC is between 1/10 and 1/2 volt, you should try
it with another battery.

My advice (assuming the battery isn't at fault) is to bite the bullet and
get a new OEM alternator or at least an OEM alternator from a wrecking yard.
Whatever's wrong is very likely in the alternator and yours has given you
faithful service for more than a dozen years. You will probably need to
replace the alternator once before the car reaches the end of life (more
than once if you put in an aftermarket rebuilt!) and this looks like the
right time.

If the AC voltage is okay and you want to try brushes rather than springing
for a new alternator, you can look in the "specialty hardware" drawers at
your local Ace hardware store. They won't have the assembly, of course, but
they have a modest selection of brushes that may be adaptable. Other than
that, I dunno. I presume you can recognize critically worn brushes - when
the assembly is removed the brushes barely protrude enough to make contact.

Mike

 

I'm joining the chorus for the alternator. Looking at the Helm manual, the
alternator internals are not the classic arrangement, where generated
voltage from the windings are used to self-excite the regulator and the
light is in series with the regulator supply from the ignition switch. In
those, brush failure is silent - the light doesn't go on because the
regulator doesn't draw current to feed the field through the brushes.

If the manual is right, the light is a warning light from the regulator and
comes on when the regulator can't (or doesn't believe it can) set the
alternator voltage correctly. That covers quite a bit of ground. The ECM
appears to come into play only through the "FR" lead - your guess is as good
as mine what that is, but my guess is that it is a "fault/regulator"
indication to the ECM.

You can troubleshoot in the car when the light is on with a DVM; the voltage
should be a shade under 15 volts DC (depending on just how cold it is under
the hood) and the AC voltage should be under 0.1 VDC. If the DC is above 16
volts or the AC is in the half volt range or above, the regulator or diodes
are bad respectively. If the AC is between 1/10 and 1/2 volt, you should try
it with another battery.

My advice (assuming the battery isn't at fault) is to bite the bullet and
get a new OEM alternator or at least an OEM alternator from a wrecking yard.
Whatever's wrong is very likely in the alternator and yours has given you
faithful service for more than a dozen years. You will probably need to
replace the alternator once before the car reaches the end of life (more
than once if you put in an aftermarket rebuilt!) and this looks like the
right time.

If the AC voltage is okay and you want to try brushes rather than springing
for a new alternator, you can look in the "specialty hardware" drawers at
your local Ace hardware store. They won't have the assembly, of course, but
they have a modest selection of brushes that may be adaptable. Other than
that, I dunno. I presume you can recognize critically worn brushes - when
the assembly is removed the brushes barely protrude enough to make contact.

Mike

 

Thanks for all the tips! This alternator is probably the original so
it's got a lot of miles, well over 100K.

Got it opened up. Brushes so worn they barely stick out when removed
from the slip rings.

Dang. One of the slip rings is very deeply grooved, can't be much metal
left. I weighed the constraints of time, money, etc. My wife's car, so
I've been driving her to work and home, 14mpg vs 28-30mpg and double
the distance, vs the difference between $100 rebuild or $20 brushes
plus $35 bearings plus $? slip rings... So I took it into a local
starter/alternator rebuild shop today.

Thanks, appreciate the help!

As far as resoldering the ECU, I have been an electronics tech for
quite a few years so I've had lots of good soldering experience. Not
for the faint of heart. Although it has no surface mount, it is fairly
dense and your average Radio Shack soldering iron is not up to the
task. And Radio Shack solder (at least in the past) uses a rosin that
is rather to aggressive for my liking.

 

Thanks for all the tips! This alternator is probably the original so
it's got a lot of miles, well over 100K.

Got it opened up. Brushes so worn they barely stick out when removed
from the slip rings.

Dang. One of the slip rings is very deeply grooved, can't be much metal
left. I weighed the constraints of time, money, etc. My wife's car, so
I've been driving her to work and home, 14mpg vs 28-30mpg and double
the distance, vs the difference between $100 rebuild or $20 brushes
plus $35 bearings plus $? slip rings... So I took it into a local
starter/alternator rebuild shop today.

Thanks, appreciate the help!

As far as resoldering the ECU, I have been an electronics tech for
quite a few years so I've had lots of good soldering experience. Not
for the faint of heart. Although it has no surface mount, it is fairly
dense and your average Radio Shack soldering iron is not up to the
task. And Radio Shack solder (at least in the past) uses a rosin that
is rather to aggressive for my liking.

 

I wanted to mention- One of the alternator rebuilders I called set
warning bells off in my head. I looked in Superpages.com, started going
down the list.

I called one, found out I was actually calling a call center 3 hours
away in Portland. That they have locations all across the country, all
under different names.

Two names listed for the same address in Tacoma, but the name on the
building is different from either of the listings. A listing for an
address in Lakewood that doesn't exist, they send you to the Tacoma
address.

No way was I going there. The only reason I can think of -not- to use
the same name is if they get a bad reputation, you think it's an
isolated location and the stink on one name can't carry over to
differently named shops in other locations. And from that one Tacoma
location with 3 name changes (at least), changing the name can escape
the stink from previous names without even moving the business.

 

I wanted to mention- One of the alternator rebuilders I called set
warning bells off in my head. I looked in Superpages.com, started going
down the list.

I called one, found out I was actually calling a call center 3 hours
away in Portland. That they have locations all across the country, all
under different names.

Two names listed for the same address in Tacoma, but the name on the
building is different from either of the listings. A listing for an
address in Lakewood that doesn't exist, they send you to the Tacoma
address.

No way was I going there. The only reason I can think of -not- to use
the same name is if they get a bad reputation, you think it's an
isolated location and the stink on one name can't carry over to
differently named shops in other locations. And from that one Tacoma
location with 3 name changes (at least), changing the name can escape
the stink from previous names without even moving the business.