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I had an interesting ride home tonight. I accidentally lowered my front passenger window a little bit and when I tried to raise it I just got a clicking noise. So I drove along hitting the button, hoping the window would close, but it wouldn’t. Then, the dash lights and head lights started pulsating/flickering. The engine power wasn’t affected and the battery gauge wasn’t moving. My vehicle is a 2002 Chevy Trailblazer with 173,0000 miles on it. Replaced the battery a few years back and have had no other electrical problems. Any ideas? Thanks.

Have the alternator checked. Pulsating and flickering are common when diodes fail in an alternator and causes it to fluctuate the voltage. The battery gauge may be buffered (a lot of factory gauges are) and not react to the fluctuation depending on the cycle of fluctuations.

Have you attempted to restart it?

BustedKnuckles - thanks for that suggestion, I will take it in (if it starts) tomorrow. How much would an alternator cost, assuming that is the problem? Thanks again.

Rod Knox - just went and started it up, no problem, no flickering.

You probably had a bad connection somewhere, maybe from the battery to the alternator or the one from the battery to the frame or from the frame to the battery.

Took it in this morning and had them check the charging system. Alternator ok, battery bad. Replaced the battery. Driving home tonight, guess what? Lights flickering and pulsating intermittently. This time it seemed to be triggered by my hitting the brakes rather hard to slow down quickly at a yellow light. I am so frustrated!! What is the right thing to ask the repair shop to look for now? Thanks again to all who answer.

Look for a braided wire that goes from somewhere on the engine to somewhere on the body. Typically it will go from the back of one of the heads to the firewall. Its possible that the braided wire pulled out of the terminal or the body under the terminal has rusted pretty bad.

There should also be two wires from the negative (-) battery terminal, one goes to the block and the other goes to the body near the battery. Again check for rust under the terminal, or the wire pulled out.

It could still be the alternator. Unfortunately, the alternator needs to be caught in the act of acting up.

I had an alternator go bad in my Toyota truck with about 14 years on it and over 200,000 miles. The alternator just stopped working and the battery light went on. Got home OK, thanks to a strong battery. Checked the charging system in the morning, and alternator tested fine. A day later, it acted up again. This time, it tested bad. Turns out the brushes were worn out and would lose contact intermittently until it totally failed.

BustedKnuckles - Another tidbit I didn’t mention before is that sometimes while at a stop with brakes on the rpms drop to the point that I have to hit the gas to keep it from stalling. I will take it this weekend to the local mechanic I normally go to mention the rpm issue, have him check the alternator again and the wires Keith spoke of (I went to the dealer today because they open early and will drive me to work). Thanks again and I just have to say I love this website.

Most GM vehicles use a junction terminal that is located near the battery. All electrical power for the vehicle goes through that terminal except for the starter motor current. (Starter solenoid power also goes through the junction terminal.)

These terminals develop scale or corrosion over time and cause all kinds of electrical grief with varying symptoms. Something for consideration anyway.

Hello again - an update and a question. After driving with lights flickering(see original post above) and having battery, alternator, terminals, grounds, wires , etc… checked out and still not having it diagnosed I am now having the alternator replaced. Today I got a warning light for the battery and a message that the charging system wasn’t working, heard a clicking noise while driving and the battery gauge was fluctuating. The question is: is $277 ok cost for replacing the alternator? Thanks.

It sounds about right.

Just because they test the alternator and comes out good doesn’t mean its any good in my experience. Had the same thing and NAPA claimed my 1 year old alternator was still good but I changed it anyway and flickering went away. I got to the point where I would not put any other alternator in in a GM unless it was a Delco rebuild. I hope that’s what they did.

Also clean the engine to body ground which should be the easiest thing if it’s the same as my truck. It’s up by the master cylinder near the air inlet. Disconnect, wire brush and reconnect. Look for other grounds under the dash. Don’t forget the usual battery connections. You might want to buy a 9 volt power source to keep your computer memory current while battery connections are off.

Thanks all. I appreciate the input.

Another update and question. Got the new alternator and now when I use the defrost or air the rpms go down to the point that my vehicle shudders and almost stalls before bouncing back up. This continues as long as I am in park but seems to go away when I am driving. I took it back today to the place that installed the alternator and of course the problem couldn’t be reproduced… so nothing was diagnosed. They said the battery, alternator, charging system was just fine. I went to work, and when I came out to go home I started it, tried the defroster and air and guess what, same problem with the rpms, the shuddering, the almost stalling… this happens while it is in park or stopped at a light. Any further suggestions or ideas?? (I have the idea of taking a baseball bat to it and junking it but it is paid for and I like no car payment. Just hate the constant problems. Maybe it’s the driver??) Thanks once again. :slight_smile:

The idle problem could be a dirty a or bad idle air control valve. How long since the car had a tune up? This could be a bad plug or plug wire. If your check engine light is on have the codes checked and post them, this will help with diagnosing the problem.

I have never taken it in asked for a tune up just have done what the dealership and/or local mechanic tells me I need to do as far as scheduled maintenance. I did have to replace the engine about 40,000 miles ago. The CEL has not been on at all - no other warnings except right before the alternator needed to be replaced and then it was something like “system not charging”. I drove it tonight and no flickering lights or any rpm problems, but I didn’t need to use the defroster.

The only thing that I can think of that would cause the engine to lug down when you turn on the defroster is the air conditioner compressor. Often, defrosters will turn on the air conditioner to dry the air before they heat it and blow it on the windshield. Your engine should have a system that makes it instantly compensate for the extra load when the air conditioner compressor kicks on. It could be anything from a solenoid that bumps up the throttle when the A/C turns on to a computer controlled idle speed that responds very quickly. Whatever it is, I suspect that it is not working.

Someone asked earlier if anyone had cleaned your idle air control valve. Idle Air Control valves and throttle bodies tend to need cleaning every 100k miles or so. Not expensive.