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Hey everyone,

While driving at night, I notice my headlights and interior/instrument panel lights seem to surge, or brighten, suddenly, and then return to their regular level of brightness normally. This only happens when I'm going 50mph+; when idling or cruising around below this speed, the surging does not happen.

The problem seems to have nothing to do with electrical load or actual engine RPM. Accelerating once the surging happens does not stop it or make it worse. I can take my foot off the gas and the behavior continues until the car itself is traveling at less than 50mph. I've sat at idle with my car's stereo cranked (including a 300watt alpine sub in the trunk, just using a pioneer HU for the front speakers), the A/C on, and the rear window defroster on, and the headlights/interior lights stay completely steady.

On a potentially related (or unrelated?) note, a bulb that lights up the intensity level of the blower speed switch on the far right of the center dash console has randomly started turning off. It can usually be turned back on by moving the speed switch all the way to the right (max), then returning it to it's normal position, although sometimes it just comes back on (or turns off) for no reason.

The alternator warning light is not on, and the car has no trouble starting.

The car has no flood history and has had one previous owner, whom I've known, who has taken excellent care of the car.

Things that have happened recently around the time the flickering was noticed:

The primary O2 sensor was replaced about a month ago at the honda dealer, as I had a CEL come on which indicated the primary o2 heater circuit was bad. Since installing the new sensor, I haven't had a problem, or a CEL. The flickering was noticed after this was installed, but not immediately after, and seems to be growing progressively worse. I can't say for sure whether the car was doing this before the sensor was replaced, but it's certainly gotten worse in the past few weeks. The sensor cable insulation appears to be sound is not rubbing against any part of the engine.

I was driving on the highway around 70mph and ran over a piece of cardboard, which got lodged under my front bumper until I could pull off and pull it out, which was maybe about 4 miles. Looked into the engine compartment and it didn't seem like the cardboard had messed anything up.

Modifications I've done since I've owned the car:

-Installed Pioneer headunit. Have examined wiring harness for bad solder joins/shorts and everything is 100% fine.

-Installed Alpine PLT-LAT 5 sub w/ built in 300w amp in trunk. Power and ground wire is sound, battery terminals are secure.

Problems were not noticed after the stereo install or the sub install.

Getting ready to take it to the dealer, and will take it to Autozone to test the bat (which is only 1.5 years old) and alternator just in case, although I doubt it's these. Any thoughts so I can avoid a huge repair bill? Something I can check/fix myself? Other than this, the car runs and drives great, but I do a lot of night driving and find it very unsettling/distracting. I also don't want to risk blowing anything electrical in the car!

Thanks!!

 
Rep Power: 246

Wow. Kudos to you for taking the time to describe all your symptoms.

Unfortuneately, it's real hard to diagnose an electrical problem without putting your hands on the car. But I'll throw some thoughts out there and maybe others can chime in with their 2-bit ideas as well.

First off, I doubt it has anything to do with your O2 sensor being swapped unless the "technician" friggen hacked around with the wires like morons. I showed my sister-in-law how to change her O2 sensor on her 99 Civic and she was able to do it herself on her own.

Since you're saying the flickering occurs at 50mph and it's not rpm related, I'm thinking that it's not the alternator (but it still could be). It sounds more like it's vibration related and at that speed something is vibrating enough to slightly short out some circuit. So check your connections at the alternator, battery, headlights, and grounds. The plugs should be firmly connected and the bolt-on connections should be removed, cleaned, sanded, and securely refastened. In particular check the ground at the thermostat housing. Also try jiggling the headlight switch on your steering column and check the connections there.

Be wary of the advice you get form the morons at Autozone or other franchise parts dealer.

 
Rep Power: 0

sql_civic, thanks so much for your reply.

I doubt they screwed something up with the o2 replacement either; only reason I took it into the dealer in the first place was the bolts securing the heat shield were stripped, and I'm too chicken to drill into anything...so I let the garage take care of it. It's securely plugged in and everything seems to be fine.

I was thinking the same thing re: vibration. The car's in the bodyshop right now getting a dent removed, but once I get it back on Friday I'll look everything over. I'm not too familiar with all of the ground points on the civic, is there a diagram somewhere with these highlighted? Where is the thermostat housing located?

Thanks again!

 
Rep Power: 0

Follow up:

Issue solved. Alternator was dying/essentially dead. Dealer confirmed after running their own diagnostics and bench testing the unit outside of the car. It still put out enough voltage to charge the battery some, which is why the car hadn't died on me yet.

New alternator, everything's peachy. No flickering, and headlights and dash lights are brighter than ever. I can actually see at night! I hadn't realized how bad it had gotten..

One quick question, if anyone knows - new alternator's output is rated at 75 amps. I uninstalled my 250 watt sub rig before having the wiring checked/alt replaced. I'd like to reinstall it and add a modest 100W amp for the front speakers. I rarely run my system at extremely loud volume. Will the replacement alt be enough to handle the total voltage needs (350 watts, max)? If not, I'll ebay the sub and put some money back in the bank. I'd much rather have a reliable vehicle than some extra bass...

 
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yeah, alternators are usually the culprits with electrical issues like these. good thing you got it done without going crazy looking for solutions as sometime is the case with electrical problems.