OT- '05 Chev TrailBlazer problem?

[Sportsterboy]

I have an 05 Chevy TrailBlazer that I am having a problem with.  When driving at night (lately) the headlights will flicker 3-4 times rapidly and then go back to "normal".  This seems to occur when either coasting or when brakes are applied (engine rpm's slowing below 2500 rpm).  At the same time voltmeter seems to drop slightly.  I have had charging system checked and battery checked at independent shop today, but they couldn't find any problem and couldn't replicate what I am describing.  I had the same problem about 1&1/2 to 2 years ago and local dealership (since closed) "fixed" the problem.  I could not find my paperwork from that dealer work to see what they replaced/fixed at that time.....anyone with similar experience or any ideas?? 

[Skin]

I had the same problem on an S-10 years ago and it turned out to be a loose ground under the dash. Tightened it up and problem solved.

[IBARider]

I actually had one come in the shop a week ago with same complaint.  Battery and connections were good.  Alternator tested good as far as volts and amps go.  However, one alternator diode checked bad according to the tester I used.  I changed the alternator and complaint went away.  Not saying that's your problem... I would have guessed bad connection myself.......

[1JITSU1]

I also think it is a diode in the alternator

[Sportsterboy]

I tried to get it to do it on high beam, but couldn't get it to flicker on highs, just low beams, if that makes any difference.   Thanks for the input/ideas.   

[Phu Cat]

If a diode's bad, wouldn't it be bad all the time?  And shouldn't Chevy be able to tell S'boy what was done to fix the original problem?

PC

[1JITSU1]

If the batt. and alt. ck out ok it could be the switch

[hdjax2]

If it was mine (and my wife has a 05 Trailblazer) before I did anything else I would add a ground strap between the engine and the frame. Many problems like the one you describe are caused by inadequate grounding. I was a driveability tech for GM for many moons and I know the additional ground strap will not hurt anything and if it cures the problem it will be a bandaid fix so to speak but it will be a permanent fix and cheap to boot. We always added one when doing transmission overhauls because more trans problems than you can imagine are caused by bad grounding also. Good luck

[Sportsterboy]

I appreciate the info/ideas.  I checked with the dealership where I bought the truck (one where I had work done has since closed).  They were able to tell me (when I gave them VIN #) all the warranty work done on the vehicle.  I guess my memory is not what I thought it was.....the work done on the previous problem with lights must have been done after warranty was up, cause they listed all the other things (3 warranty items) that were fixed at the closed dealership......

[86fxwg]

Theres 2 t.s.b,s concerning head light flicker on gm vehicles.T.S.B#1. 05-08-42-001 T.S.B#2  06-06-03-004.#2 pertanes to air pump load. Sertch these on the GM website.Hope this helps.

Dave

[Sportsterboy]

Thanks....the shop mentioned finding the air pump (load) on a service bulletin search.  It mentioned that it pulled 35-40 amps and can cause the flicker which is considered "normal"....I will have them look at the other TSB....