Ok so I bought a 2000 Honda Civic EX for $1700 and it had the check engine light on and the guy told me that it was just for the o2 sensors. But when I got the codes again after replacing the o2 sensor and switched out the ECU for the P28, it said that I had a code 17 (speed sensor defective), code 20 (ELD defective), and code 41 (Primary o2 sensor defective). So I replaced the whole fuse box and it STILL has the codes! Oh and I also already replaced the speed sensor.

So here is what the car does: when the car is cranked the lights in the car dim and even my headlights do like a flashing dim. Im pretty sure that the car had a sound system in it and from what I've read about other people having to replace the ELD had a sound system too. But iono what to do now! SOMEBODY PLEASE HELP!!!!!

 

You should check for any hacked up wiring and wiring that can be rubbing against the frame (intermittent shorting).

 

Fluctuating voltage is often because the alternator is not getting powered up on the I wire (black and yellow), which should be energized when the key is on. It comes from a fuse under the dash. The same circuit also powers the speed sensor and oxygen sensor, so lack of power will cause sensor codes even though the sensors themselves may be OK. I assume that the speedometer does not work. You need to see why that wire is not powering up. I guess the wiring has been hacked considerably since you have an OBDI ECU in it.

Like gwl said, the 1996-2000 models have a trouble spot where the wire harness on the back of the engine (to the alternator) goes through the bracket that braces the bottom of the intake manifold to the engine block. It can get frayed there, short out, and blow the fuse #15 under the dash. (Search for "fuse 15 problem" it is very common). You really need to get underneath the car to see that part.

 

Thanks everybody but it was the #15 fuse. Its crazy how a 10 amp fuse can cause so much trouble!!!

 

If the fuse was blown you really should get under the car and tape up the wires. It's just going to blow again.

 

Will do