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96 Honda Civic Electrical Problems

I have a 96 Civic with 232,000 miles. I have regular maintenance done and just had the third timing belt put on. When my husband and I returned from vacation (about 2,000 mile trip) the check engine light came on, the spedometer went crazy, and the headlights and interior lights were blinking. Took it to my mechanic and he pulled the following codes - PO500 (Vaccuum Switching Valve), PO135 and PO141 (O2 sensors), and P1298 - (ELD High Input). He checked the alternator and it would read low when idling, but pegged the meter when he stepped on the gas. He checked and cleaned the battery, checked the fuses and put two different rebuilt alternators in, but didn’t fix it. He replaced the fuse box assembly under the hood. This contains the ELD (electric load detector) which is a little brown box within the fuse box. This seemed to fix it and I picked it up yesterday. Drove it home and everything was fine. I drove it just a few blocks this morning and the check engine light came back on and the CD player/radio was acting little funny. I plan to take it back to my mechanic on Monday.

Any ideas as to what this problem could be? We drove through a severe thunderstorm with lots of lightning on our way back from vacation. Could this have something to do with it?

The codes P0135 and P0141 state there is a problem with the circuits to those sensors. I assume the voltage from the replacement alternator stays between 13.3 and 14.8 volts. Check the AC voltage also while the engine is running and make sure that it is below 0.1 volt.

You could help your mechanic by writing the current problems down, in detail, and giving him that information. Past problems are not forecasters of current, or future, problems.

Added: The AC voltage Cougar is referring to is alternating current (ac); not Air Conditioning (AC). There should only be dc (direct current) in ALL circuits; and, no ac. The alternator is supposed to stop all ac.

Yes, my mechanic said the alternator was working ok. I’ll have him check the AC voltage. I don’t know if it matters, but when I drove it after I picked it up from my mechanic I didn’t have the AC on.

When Cougar said check the AC voltage he wasn’t referring to air conditioning, he meant Alternating Current. Basically, if the voltage on the battery were rapidly bouncing up and down it could be due to a bad alternator diode. But since the alternator has been replaced that’s not likely the problem.

I think it’s still got a bad electrical connection, possibly a ground strap between the engine and body.

Thanks for the clarification about the voltage.

As far as what my current (as opposed to past) problems are, they are the same as what I brought it in for the first time - check engine light, speedometer not working, and lights blinking. My husband said he noticed the radio acting funny before I took it in the first time also. It seems that what my mechanic did to fix the problem didn’t work. Sorry if my question/explantion was not very clear.

Thanks for the clarification! Obviously I need all the help I can get. I’ll have my mechanic check the ground also.