mRahmani

I have a '92 Civic DX with 260k miles on the clock. A while back, I was driving around 45mph when the CEL came on and the engine instantly shut down, as if I had switched off the key. It will crank just fine but has refused to start ever since. I replaced the spark plugs, distributor cap, and rotor, though a little research since then tells me that would have no effect on the problem. The CEL stays solid regardless of whether the diagnostic port is jumped or not.

I tried replacing the ECU with a unit I got off Craiglist, but that made no difference. I suppose it's possible that both units are bad but I'd like more info before dropping $50-$100 on a third one. I checked the ground at the thermostat and it looked like it was on tight. What else can I look into? And is it likely for an ECU to suddenly and catastrophically fail like this with no prior warning? The car has never had a CEL or performance issue since I bought it a few years back at 210k.

HondaPartsHero

Did you open them up to see if they look burnt?

Former User

Start by checking whether 15A hood fuse 31 or dash fuse 24 is blown.

apexi_rsx

sounds like u have a wiring problem and your frying ecu's. have you looked over your wiring harness to see if there are any bare wire's that could be grounding out on the chassis? as ron said check your fuses and see if any are blown if so report back what ones they are

mRahmani

Thanks for the responses guys!

I took a couple pics of the second ECU, haven't cracked open the original one yet:



This looks OK to me at first glance, but is there something particular I should be looking at? I didn't see any cracked/leaking capacitors.

I'll check over the fuses and wiring when I get back tonight and let you guys know what I find.

mRahmani

Update - I checked the fuses, they looked good. Same with the wiring harness as nearly as I could tell, I don't see bare wires touching things anyway.

One thing I did notice is that as soon as I turn the key to "on," the fans start on and won't stop till the battery drains. I didn't hear the main relay(s) click when I turned the key.

I also replaced the ignition coil, which didn't do anything. So far - new dizzy, rotor, coil, plugs.

Former User

Unless you are wealthy, stop replacing parts at random. You're just wasting money. Start doing diagnostic tests that save money. You need to check installed fuses 31 and 24 for voltage with a test light or multimeter. Click and read the Fuses link in my signature.

The fan runs because somebody unplugged and inserted a jumper wire into the fan switch connector on the thermostat housing.

mRahmani

I just checked all of the fuses with a multimeter, they were all good. Any idea what I should look at next?

honda fossil

code 0 dosen't all ways mean a bad ecu. also check for a loose or poor connection of the ecu power wire ,a short in the combo meter

Former User

There's only two fuses to check. How did you test them and what did you find?

mRahmani

I used a multimeter to check for resistance (set it to read 200 ohms) and touched one end of each wire to the small metal test points on top of the fuses. The meter read 1 when it wasn't connected to anything and about 0.002-0.004 anytime i touched both ends of the fuse. I figured as long as I was checking fuses I might as well check all of them, so I just went through each one under the hood (in the box by the battery) and the ones under the dash.

Former User

A resistance test of a fuse is okay, but it only tells you half the story. If you instead test for battery voltage to body ground at both tabs, then you not only learn whether the fuse is good, but also whether it gets voltage. If there's no voltage, you have identified a problem.

mRahmani

Just to make sure I know how to do that correctly - I would need to turn the key switch to "On" to and then test for voltage, right?

Former User

Yes. Did you click the Fuses link in my signature?

mRahmani

Well I checked the fuses for voltage and got a big fat 0 on every fuse I tested. I checked the battery itself for my sanity's sake and that read 13.5, so while it's weak at least I know there is voltage in the system and my voltmeter is working properly.

What should I look at next? Or did I test the fuses wrong again? Key was set in the "On" position when testing.

Former User

Describe how you tested voltage at the fuses. You need to test voltage at the fuse tabs as described in the Fuses link in my signature.

mRahmani

I don't have a test light, I was using a voltmeter with one end touched to each test port on top of the fuse.

Former User

HOW did you measure voltage with the voltmeter? Where did you touch the two meter leads?

mRahmani

I touched one end to the left-side test port and one to the right-side one, just like I did when doing the resistance test.

Former User

The way you did the test, you would read 0V even if the fuse had battery voltage. You did the test wrong because you resist reading the Fuses link in my signature. It's difficult to help you if you won't follow directions.

mRahmani

I did read the link. Several times. It only mentioned how to test for resistance or with a test light, not how to check voltage with a voltmeter.

Former User

Testing voltage with a test light or voltmeter is exactly the same. You are not following the directions at the link. Where does it say that testing voltage involves touching the leads to both of the fuse test tabs? Read the information carefully. After rereading it again, ask a specific question if there's something you don't understand.

mRahmani

OK, I don't understand what I'm doing wrong. I tried testing using the method it described for a test light, touching one end to the top of the fuse and one end to a metal ground. I still get nothing from either the left or right terminal of the fuse. What am I screwing up?

Former User

What is your multimeter set to? Post pictures. What metal are you touching for ground? Post pictures.

What voltage do you read when you touch the meter probes to the battery posts?

mRahmani

OK, I'm not sure what I did wrong the first time but I was able to get some readings this time. Pics of the setup I was using:

Multimeter


Battery reading - car has a dead battery and was being jumped for this test


Ground - I used the bolt next to the top of the shock absorber


Fuse points used


What I found was that the under-dash fuses were all working ok, getting between 12.5-13.5 volts. However, the under-hood fuses were all getting 0.5-1.5V - not just the 15A ECU fuse, but all of the fuses. I'm guessing those are also supposed to be reading in the 12V range, right?

EDIT: Forgot to mention, the ground I used for the under-dash fuses was one of the bolts on the driver-side door.