Honda
Civic ECU blew a capacitor.
Civic
blew capacitor after driving for
short period led to stalling.
After a long rain
yesterday, this morning I got into my Civic,
started it up and got just out of the drive
way when the engine suddenly stopped and
smoke began to emminate from the passenger
floorboard / glovebox area. There was the
smell of something burning - but I was unable
to find the source of the smoke. After that,
then engine would rotate upon cranking, but
not start. There were no codes flashing when
I put the jumper in. I just rebuilt the
distributor several weeks ago (bearing
replacement) & its been running fine
until today. Could this be the ECM blown, or
what? Thanks, Paul
First check to make sure that all fuses are of
the correct amp when none are found blown. A
wrong amp rating will cause a smoky-short like
you'd describe when there is a short somewhere.
But if the fuse is of correct amp ratings, this
shouldn't happen. There are things you must do
next. Get a wiring diagram (usually from a
service manual) and probe to see if power is
supplied to coil, ignitor, main computer, main
relay. If there are power to the main computer,
and the computer is not powered up then a ground
wire is burned up and open. -H
I checked the fuses &
all fuses in both boxes were of correct
amperage. When you say "main computer",
do you mean the ECU in the passenger front
flooboard area? I was thinking of removing
this unit and the glove box to see if I could
find a burnt wire somewhere - since that is
where the smoke was emminateing from. How can
I tell if its "powered up"? If the
"check engine" light is on, does
that mean the ECU is powered up? The "check
engine" light comes on when the key is
turned, but again, no error codes. I do have
the Haynes manual which has some limited
wiring diagrams - so I can do some probing
around. What is the main relay and where is
it located? Paul
Can you describe the smell of
the smoke? The area you indicate is where the ECU
is located. If there was smoke it doesn't sound
good. Pull back the carpet to reveal the ECU. On
my '90 Civic the red LED in the "window"
makes a brief flash when the ignition is first
turned on. If the ECU got fried I would
definitely try to locate the cause before I
replaced It. -Joe
To look for a short is simply look for wire
that appears sticky and melted. Until you find
this wire and replace it, don't attempt to
purchase a new ECU and put it in. On the other
hand, there could simply be a circuit inside the
computer that's fried. It wouldn't be hard to
look for that since it would look burned
especially on the flat side of the circuit board.
Almost all the time, I hardly come across a burnt
transistor to show any signs of charring. So you
have to use a probe, or try to recreate the smoke
and quickly keep an eye where the smoke is coming
from in the circuit board or wire harness. -H
Thank you all for the help
and insight thus far. Here's the status: I
had just replaced the battery several weeks
ago - posts are clean & all. But I looked
under the battery anyways & could see no
evidence of a chemical leak or burn and no
burnt wires. Next I pulled the glovebox &
looked under there for burnt wiring and could
see none. Sniffing around pointed to the ECU
as the source of the still-strong burnt smell.
So I pulled the ECU. None of the wires going
to the ECU were burned or showed any signs of
melting. Next I pulled aprt the ECU and low
& behold - a spot on the platic that goes
between the under side of the circuit board
and the metal backing had a nice 1cm burn
hole with blackened areas all around it.
Looking at the board, I can see that a 220uF,
35v capactior near to where the wiring
harnesses connect has blown. Also, it appears
that at least 3 adjacent traces on the PCB
are burned so badly there is an open there.
Right now my theory is the cap blew out,
opening up a few of those traces, resulting
in some faulty ECU circuitry. My question now
is what to do. I think I can get a
replacement cap - & I can jumper those
open traces by soldering some wires in, but
is that gonna be enough - or is that too easy?
How does my theory sound? -Thanks, Paul
Good catch! Your method sounds
good. Try it. -Subversion
welp - I did the repair
& plugged the ECU back in w/ the cover
off so I could observe. I found that there is
something causing the cap to go because my
solder started to melt - I immediately turned
the key back off. Alls I can tell is there is
a yellow wire w/ a black stripe that comes
into the middle harness & feeds the cap
that is blowing. I will try to explore where
this wire comes from, but I'm not too hopeful.
:( -Paul
The yel/blk wire is the main
power line coming from the main relay. It goes to
the EACV, fuel injectors, purge cut-off solenoid,
and the ECU. Trace for shorted circuit board. My
guess is that a short on the circuit board
discharged the Cap too fast, and blew it up. -Subversion
I would not try to turn on the ignition for
longer periods after the first try. Now you know
that it's a short, you need to look for the short.
Turning on the key again might do more damage.
But turning on the key is the only way to know.
It now appears that some of the ECU internal
components or external sensors are damage and
sending Yellow/Black wire directly to ground.
Yellow with black stripe is almost always known
as the power wire. It comes from the injector
resistor, O2 sensor and the Main Relay. All
assuming that you'd replaced the capacitor and
components adjacent to the capacitors, or which
ever was faulty. -H
Yes. That is right. It was
a problem with the circuit board and when I
replaced the cap - I re-connected it
incorrecly because I dodn't have a schematic
& went based on best guess. The problem
now appears to be solved and the car runs. I
am now laying a coat of Elmer's glue over my
mods to hold stuff in place and protect
agains further shorts. There must be
something better than Elmer's for this, but I'm
sure I don't have any, whatever it is. To
determine the problem, I tested the yellow
& black wire for +12 & it was there.
So, I assumed the problem was with the board
and began to look more carefully at the paths
and vias. Because the old cap blowup did so
much damage, it was difficult to tell what
went where & I actually had to try a few
different connections to get it right. Who'd've
thunk it? The PCB actually went faulty on its
own, evidently. Listen guys - you've been an
awsome help & it is very unlikely that I
could have done this without your kind advice.
Much appreciated! -Paul
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