07 Impala Flickering Headlights

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Thread: 07 Impala Flickering Headlights

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    3.0 Liter SIDI V6 WannabeRich's Avatar
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    07 Impala Flickering Headlights

    A few weeks ago I bought a new Impala LTZ. I just took it for a trip to CA for the holidays. So, I left when it was still dark. I noticed that the headlights and dash lights were noticably flickering. I thought is was maybe because I had my cell phone plugged in or something. Anyway, what I finally discovered is when the engine goes into 3 cyln mode, the lights flicker and continue to flicker as long as it stays in 3 cyln mode. As soon as it goes back to 6 cyln mode, they stop flickering.

    Any of you 07 Impala 3.9L owners have this problem? Any of you techs heard of this? This cannot be a normal thing. Looks like I'm headed for a trip to the service department.
    Last edited by WannabeRich; 12-26-2006 at 08:36 PM.

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    Re: 07 Impala Flickering Headlights

    The flickering is a function of the PCM running the alternator. The alt. field is switched by the PCM roughly 400 times/min, this only runs the alt as needed as a way to better fuel economy, my 02 silverado does it as well as most GM vehicles. There are TSB's out about this but if the alt is putting out an average above roughly 13.5 V then it tells svc dept to inform customer about PCM controls
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    Re: 07 Impala Flickering Headlights

    How do you know if you have one of those "computer controlled" alternators? I've noticed something similar on my '05 Impala, but it also seems related to idle-speed, so I figured that was the issue...(and thus nothing to worry about).
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    Re: 07 Impala Flickering Headlights

    Quote Originally Posted by ockgator
    The flickering is a function of the PCM running the alternator. The alt. field is switched by the PCM roughly 400 times/min, this only runs the alt as needed as a way to better fuel economy, my 02 silverado does it as well as most GM vehicles. There are TSB's out about this but if the alt is putting out an average above roughly 13.5 V then it tells svc dept to inform customer about PCM controls
    Thanks for this info, ockgator. Sounds like you are implying this is a normal situation. If my dealer's service department tries to tell me that, it will not go down well. That is an unacceptable condition.

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    Re: 07 Impala Flickering Headlights

    Replace it with a Delco Remy. Delphi garbage...
    '07 Subaru Forester 2.5X 5MT. Bought new. 164k miles. '05 Dodge Durango Limited Hemi AWD. Mom bought new. 90k miles. '74 Buick LeSabre Luxus convertible. 455/7.5L, Quadrajet, dual exhaust. '89 Buick Reatta. 3800 SII L67/F40 six speed swap to be completed someday.

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    2.4 Liter SIDI ECOTEC ockgator's Avatar
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    Re: 07 Impala Flickering Headlights

    Delco is now Delphi. The original TSB's were for the Venture and Montana mini vans, expanded from there. If you have access to an oscilloscope and watch the field volts being switched you'll see what I mean. On a scanner it'll read alternator duty cycle.

    I don't like it either, but I've seen same thing in Toyotas and Hondas. Any little thing to raise CAFE ratings.
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    Re: 07 Impala Flickering Headlights

    Update: Finally got the car into service for this problem.

    #PIC4354A 12-22-2006:
    2007 Impala/Monte Carlo only equipped with LZ8 3.9L engine.

    Recommendation/Instructions: This is an emerging issue that is currently being reviewed by Engineering. At this time there is no service repair for this concern. Do not replace any parts. It has been verified that replacing the generator will not repair the light flicker. Please call TAC and set up a case to assist Engineering in tracking and collecting information on this concern. This PI will be updated when new information is available.

    This is a proactive PI. When a TAC case is set and the service repair is available your dealer will be sent a DCS message.

    Well, at least I did not get the old "could not recreate the symptom" explanation.

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    Re: 07 Impala Flickering Headlights

    Seems to me that they could have avoided this whole issue simply by putting capacitors on the lighting circuits..

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    Re: 07 Impala Flickering Headlights

    Quote Originally Posted by WannabeRich
    Update: Finally got the car into service for this problem.

    #PIC4354A 12-22-2006:
    2007 Impala/Monte Carlo only equipped with LZ8 3.9L engine.

    Recommendation/Instructions: This is an emerging issue that is currently being reviewed by Engineering. At this time there is no service repair for this concern. Do not replace any parts. It has been verified that replacing the generator will not repair the light flicker. Please call TAC and set up a case to assist Engineering in tracking and collecting information on this concern. This PI will be updated when new information is available.

    This is a proactive PI. When a TAC case is set and the service repair is available your dealer will be sent a DCS message.

    Well, at least I did not get the old "could not recreate the symptom" explanation.
    Cool good to hear. Hopefully they will have a fix soon.

    2002 Chevy Monte Carlo LS 3.4L (Loser Series ) 35MPG

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    Re: 07 Impala Flickering Headlights

    this is a normal function for the car.

    yes it is noticable.

    first one i ever seen i threw a cluster at it. never came back. it had what you described but the headlights didnt flicker. just the cluster lighting.

    but yes as described above they found that the alternator is the cause for this. as well as the computers


    alternators now days cant keep up with all the junk we have on cars.
    you see these 160 amp alternators that are water cooled, just imagine in a few years.

    look 5 years ago. maximum you would see on a car was maybe 100 amp. maybe 110.

    now we have 140-170 amp.

    its crazy. we dont need any more electrical things on cars.
    its nice for business because it will always break down, but its just getting crazy
    Last edited by Triple-X08; 01-25-2007 at 01:59 PM.
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    Re: 07 Impala Flickering Headlights

    Keep us updated as to your status and whether there is a fix available.

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    Re: 07 Impala Flickering Headlights

    Quote Originally Posted by Triple-X08

    look 5 years ago. maximum you would see on a car was maybe 100 amp. maybe 110.

    now we have 140-170 amp.
    True, my 1996 Rodeo that I had, had only a 60 amp alt.
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    Re: 07 Impala Flickering Headlights

    Quote Originally Posted by F14CRAZY
    Replace it with a Delco Remy. Delphi garbage...

    Well, most GM's do come with garbage now for electrics...

    Denso, Valeo or Siemens...take your pic...

    We never had unrepairable issues like this with a Delco/Delphi alternator...

    Never...

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    Re: 07 Impala Flickering Headlights

    Quote Originally Posted by GMCSonoma
    Well, most GM's do come with garbage now for electrics...

    Denso, Valeo or Siemens...take your pic...

    We never had unrepairable issues like this with a Delco/Delphi alternator...

    Never...
    If I understand correctly, it has nothing to do with the alternator itself.. Instead the computer is shutting off the alternator to reduce drag, which causes the car to intermittently run off the battery. So it's basically the same thing as when you shut off the engine, and all the lights dim. If that's the case I don't see why they couldn't just issue a software update. Unless the alternator can't handle running continuously, or it would impact fuel economy significantly.

    I also wonder how this affects battery life.. Car batteries are made for brief high-current loads (the starter); they don't handle sustained low-current draws as well. That's why trolling motors use special "deep cycle" batteries.

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    Re: 07 Impala Flickering Headlights

    Quote Originally Posted by rearden82
    If I understand correctly, it has nothing to do with the alternator itself.. Instead the computer is shutting off the alternator to reduce drag, which causes the car to intermittently run off the battery. So it's basically the same thing as when you shut off the engine, and all the lights dim. If that's the case I don't see why they couldn't just issue a software update. Unless the alternator can't handle running continuously, or it would impact fuel economy significantly.

    I also wonder how this affects battery life.. Car batteries are made for brief high-current loads (the starter); they don't handle sustained low-current draws as well. That's why trolling motors use special "deep cycle" batteries.

    In that case...many BCM's are no longer Delphi/Delco...but also Siemens & Valeo...


    IMO, GM should look again in it's own backyard...

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