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Hello- I have 2003 Civic lx. The other day driving home from work the bottom bolt of my alternator snapped off and after driving for an additional 10 minutes my car died, as expected. Since I need to replace the bolt, I decided to take the alternator to autozone to get it tested. The alternator failed the test and I got a replacement part from autozone. I got home, put the new alternator on and jump started the car and my electrical problems began. The car started just fine and car battery seems to be holding the charge since I can start it without a jump. However, my check engine light is on now, my RPM gauge and tempeture gauge don't work. Additionally, the green security light is blinking as the car is running. Also, the car runs like crap and does not rev more than 3K rpm. I had a friend bring over a computer to get an error code from the car but he gets an error code (no communication) and can't link. I'm lost here. I checked all the fuses which seem to be okay. Any suggestions??? please, please help. I am trying to avoid honda's $100 per hour analasys.

 
Rep Power: 253

Make sure your alternator belt is tight

Check your battery terminals and get your battery tested.

 
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I checked the belts and tested the battery. Still no luck.

 
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Anyone else? please...

 
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The green security light by chance are you talking bout the immobilizer light on the cluster. You might need to switch the immobilizer off/on or whatever, forgot which one it was you need to do. Could be a bad ground so check all your grounds.

 
Rep Power: 511

What code is throwing the CEL you got goin on? That would help a little bit in diagnosing your problems.

edit: I just read that your buddy tried getting the error code.. try getting it read at an autozone?

 
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I brought the car to a couple of places but no one can get an error code. I can't get any machine to link with the CEL. The green light on the cluster. I think it's the security indicator and it blinks as the car is running. The car is running in safe mode and I have no power to the CEL. Could it be a bad ground? does that cause the car to run with minimal capabilities? The RPM and Heat gauge are still not working. However, I can run the car even if I disconnect the battery.

 
Rep Power: 214

Does the green light in the shape of a key if so its your immobilizer. And ya its possible it could be a ground. A bad ground can make all kinds of things go wrong.

 
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It is the immobilizer. How can I prevent the immobilizer from staying on? is there a sensor causing this issue? I'll check the grounds and report back.

 
Rep Power: 214

The immobolizer can only be turned off from the ecu. So you might want to go to honda or find someone that knos about immobilizers. The immobilizer is there for anti theft. If it blinks while the car is on and does not turn off for a while then it does not recognize your key. If the immobilizer just stays on and does not blink but just stays on then the car will not crank at all. This might be your problem.

 
Rep Power: 511

It really sounds like you got loose connections at the ECU.. that's probably why you can't read the CEL code, throwing the CEL in the first place, and putting your car in limp mode..

 
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Just had my mechanic tell me it's the computer. I am getting the part from a local junk yard for $100. I'll let you know guys know if this solved the issue. Thanks for everyone who commented.

 
Rep Power: 511

Someone correct me if I'm wrong, but I think you're gonna have immobilizer problems (i.e. car won't start) until you flash your key to be programmed with the new ECU..

 
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The mechanic told me the same thing. Does anyone know how the programing is done?

 
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Requires software on a laptop, there are key companies that will do this for a lot less than the dealer. Obviously they have to be local to you, but this company made me new keys in my area. http://www.ekeys4cars.com/home.php

 
Rep Power: 214

You are correct there. The immobilizer is in the ecu which runs up to the ignition and it only recognizies the key that is programmed for that ecu. And if you do not have the key then it will not start.

 
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Had my mechanic change the ECU and had it reprogrammed. That solved the issue. Thanks to all who contributed.

New alternator, new battery & a used ECU (junkyard). Total cost $650 (parts & labor)

 
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I've had the same problem, mine actually just went into limp mode about thirty minutes ago, it definitely has to do with the alternator and the alternator belt. If the belt slips out or if the alternator bolt breaks like yours did and mine did the first time your car will go into limp mode until you get a new ecu and program your key to the new ecu. This is my fourth of fifth one and its gotta either be a short in a ground wire or something to do with the alternator. If you just go to a Honda dealership with your new/used (whichever was not on YOUR car previously) they should just stick it in and reset your key for like 15/20 bucks. But while your car is in limp mode your rpms, enginge temp gauges wont work, your car will guzzle gas, no a/c and wont be able to go past 60-65, have to change gears every 10 mph through the first 4 and the 5th gear will get you to 60 as long as you press the gas lightly. It's pretty lame for sure. There is some place online you can order a used ecu and it comes with like a 3 year warranty if you buy it, and if this happens again you can just send in the one the went bad and they will send you another used one for free, when i find the sight ill post it up here.

 
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That's exactly what I went through!! Do you think the ECU really went bad? Do you think a ECU reset would of done the trick?