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Honda Civic ECU blew a capacitor.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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