Pope6666

Hi
I changed the battery on my 99 Accord, and the horn went off continously. Eventually i ended up pulling the horn relay out. Then in my panic having woken the street i reconnected the battery (a 3rd battery) the wrong way round. I replaced the blown 100 amp battery fuse and put the horn relay back in (and it didn't go off). Car started with no other apparent electrical damage, except radio is not asking for code (radio dead) and no red light in corner of radio unit (standard Accord radio). i checked 20 amp radio fuse at end of dash.

So my questions are how to a get the radio to come back to life (i have the code). i already tried removing radio/cigarette lighter 20 amp fuse for 20 minutes. I'm relunctant to disconnect battery again in case i set alarm/ horn off. If i do have to disconnect the battery, is the procedure just to remove horn relay, then disconnect battery and then replace horn relay.

I have 2 key fobs (both of them have good batteries in and the little red light comes on when you press the buttons, but niether seem to activate/ deactivate anything on the car). So i rely on the key to open doors

Any help greatly appreciated. Thanks

jdowen2

Does accessory socket have voltage? If not, check driver's underdash fuse relay box, fuse No. 8 (7.5A)

Pope6666

Hi, thanks for your reply

Yes the both the 12 volt accessory socket and the cigarette lighter are working. fuse 8 ACC relay drivers side ok; fuse 9 passenger side radio and cig lighter working; and fuse 13 under bonnet backup ACC ok

any other suggestions. thanks

jdowen2

Pass. Multiplex Control Unit has control of keyless transmitter (LOCK, UNLOCK, and TRUNK), pass. door LOCK and UNLOCK, and security input for the radio. Possible your MCU is fried.

Pope6666

Thanks for the reply. How can i diaganose if the MCU is shot? Only thing to point out is the radio worked before i did the battery change but the key fob functions (door lock unlock etc) didn't......I'm not bothered about the keyless door functions...just want my radio working again!!!!

jdowen2

You should be able to program key fobs to unlock, lock doors. https://honda-tech.com/forums/showth...ng+transmitter To test radio you will have to put test batttery on pin B4 of harness coming out of pass. side multiplex unit.

Pope6666

Thanks, disconnected battery and when reconnected horn didn't sound, still no radio but the fobs work now...lock unlock, red light on steering column flashing....but still no **** radio!!!