Cashkidd720

So, I have a 2004 civic lx non vtec. I fried my ecu last week due to a loose alternator, or so i thought. I was driving in high rpms and the battery light came on and then the CEL would flash once, followed by the a relay clicking behind the glovebox. Rpms would fall everytime the CEL would flash and the relay would click. I noticed when I popped the hood the alternator bolt was loose, and the alternator had some play in it.
I hooked up a scanner to the obd port and couldn't establish a connection multiple times. So I read online that the alternator bolts ground out the alternator and if they are loose it can fry your ec, so I replaced the ecu myself, had Honda flash my keys and the car ran fine...for about a week. It threuw a cam position bank 1 code right off the bat, but I reset it and just kept it under 3k rpms when i drove it. I decided to see if it would come back on next time I went into high rpms, so I went from 3k rpms to 4irons slowly through 1st and 2nd gear and had no problems. After that I came to a stop and got on it from from a dead stop out of first, once I got around 3500 or 4500 rpms it fried the ecu again, relay clicking, CEL flashing with relay, limp mode, rpm guage and temp guage don't work.

New ecu was exact one for my model, the alternator it tight, did NOT change the cam position sensor. The battery light has come on both time the ecu fried.

Any helpful info appreciated thanks again. -Ian

ELD? Multiplex Unit? Alternator messed up because of the first surge?

Cashkidd720

Bump

toyomatt84

iTrader: (1)

I would say that your alternator is causing issues at this point. I don't think your ECU is fried, though... maybe just a short in the wiring to the OBD2 port.

Cashkidd720

I feel like the CEL flashing with the relay(main behind glovebox) clicking over right behind it, is a tell tale sign the ECU is shot. Same symptoms as last time. Thanks for the help. Going to replace alternator and ECU this weekend. (ECUs are $80-120 @ the junk yard)

Maugutus

I've had this issue in my car. The alternator bolt has come off twice. The first time it fried my ecu I had to get it reflashed and it was a pain! The second time I had grounded the alternator using the small 3" bolt it has on the housing and it didn't fry the ECU. The large bracket mounting bolt is in fact the ground for the alternator itself using the housing. I replaced the bolt using a starter bolt that I bought in a 3 pack at AutoZone. I also bought a locking washer, then torqued it to 14 ftlbs. I then put some ultra black on the tightening bolt under the alternator housing. I also ran a new charge wire from the alternator to the battery. This made sure it wouldn't come off again because the starter bolt set at Autozone is slightly larger, the belt (and bolt) are secure and it has no way of loosening. Even if it does it is always grounded. And the alternator couldn't short out.

Basically just ground your alternator using a small wire to the valve cover, or timing cover and make sure you don't over-torque the alternator bolt by too much and you don't tighten the alternator belt too much. Both will cause the bolt to loosen slowly, and subsequently fry your ecu. The alternator could also be broken, but to be completely sure do this with a new alternator, because the threads might be bad on the alternator bracket.

Funny thing is my cam position sensor was also shot. Possibly caused by the first time the alternator fell off. I replaced it as well.

Bryce De Waal

Hi I am having the same issue, except it keeps happening... About 2 months ago my car was misfiring slightly once in awhile and was not a big deal until the alternator came loose about 2 weeks ago which killed the ECU. So I remounted the alternator and ran a headbolt through the other side with the header removed, and added a nut to the other end with a ground strap to the body. I got myself a new ecu and she was running fine. I notice the misfires again and then the car would randomly enter limp mode and rev limit around 3k. (ive already replaved crank sensor, cam sensor, map sensor, cleaned egr, replaced pcv, cleaned iacv, replaced all coil packs and spark plugs) Just today it started to enter limp mode except the tach started to go out... as soon as that happened I heard the horrible sound of that blue relay behind the glove box ticking and sure enough... the ecu is dead again except this time my alternator is STILL MOUNTED! Im using the same one that this happened with but it is still mounted and the groundstrap is fine....... what is going on here I really need help..