Crazy sensor/wiring/speedometer problem with my 98 civic
 

Hey guys, heres my problem, I got a 98 civic 2 door coupe 5 speed, been drivin the car all day and its fine, I go into McDonalds to get something to eat before work, i come out start my car and now the check engine light is on, so yea thats fine it happens, then I back up and start going forward, now i notice my speedometer is going berzerk!! The speedometer is going crazy left and right. So after work I also notice that the headlights as well as the guage lights are sort of flickering. So now this is really weird, so I go to a buddys from works house and he has a code reader so they come out as codes P0135 and P0141 which are both O2 sensors. Wtf? i thought it would be the speed sensor or sumthing...im puzzled cuz I dont see why they would both malfunction like that and why everything else is so screwed up, i think it must be a wiring problem. So im just wondering if anyone has any ideas or insight, or maybe this happened to you. Any help would be greatly appreciated!

Well first I would clear the codes, and make sure al the connections at the back of the cluster are fine.

Is your speedo always jumping around?

And dont think just because both o2 codes are on that its a wiring problem. I've had 3 failed o2's on one car before, they were all bad. But usually something causes this, anti-seize, silicone, bad gas, etc.

But first clear everything and check connections.

Hey thanks for the reply.

Well I decided to take it in, and it turns out the alternator was dieing, and the battery was discharging which was draining power and I guess caused a fuse or 2 to blow which caused the problem with the speedomoter and the lights as well as that check engine light with the O2 sensors. So its all fixed now.

Never seen a honda alternator cause that.. thats a first.

Glad it got figured out

I have exactly the same symptoms in my 97 Civic that I have been trying to trouble shoot. What is the easiest/best way to check the alternator.

Take it to a shop and have an AVR test done. It checkes the voltage that the alternator puts out. 10 to 1 its the resistor pack in the alternator thats usually gone. Once the pack goes, it either under or over charges the electrical system. Sounds like this is an over charge. Under charge, the battery would usually die.

the 96-00 civics have a wire chaffing issue on the back of the IM that blows the alt fuse and therefore get the described problems above.
i had it happen to me.
take it to honda its a known problem, they'll fix it