Flickering/pulsating headlights on my 2002 GT

[guitarfish]

My 02 GT has had this problem for years: when driving at night, if I coast, the headlights will flicker / pulsate, about once per second. They don't go completely out, but they have a definite flicker. As soon as I hit the gas a little it goes away. When this happens, I've tried turning various things on and off, e.g. heater/AC, fans, etc. Nothing seems to affect it one way or the other.

Electrical isn't my area. Is there a headlight relay or something that could be bad?

[bluebowtie67]

well, I don't have any clue as to what it is but I'm also having the same problem.. and have been for years. hopefully someone knows huh...?..

[BNaylor]

Make sure your battery is good (get it tested) and check the alternator for proper output. Also, check the positive and negative terminals at the battery and the cables.

In a worse case scenario you could have an ignition switch with arced out or carboned up contacts. Carbon acts like a resistor causing a voltage drop or arcing in the circuit seen under load. Headlight flicker is one possible symptom.

BTW - There is no headlamp relay. The low and high beams are controlled by the multifunction switch (MFS - Stalk) which is another possibility.

[guitarfish]

I installed a new battery 2 mos ago, and cleaned the cables at the battery at that time. No change in the symptoms, so I feel confident it's not a battery issue. With 158,000, my alt. could go anytime now, LOL, so I guess I'll know sooner or later if that makes a difference.

Will keep you all posted.

[Den69RS96]

My 2002 Gt does that as well. I'm told it is a erratic voltage issue with the alternator. You could try replacing the alternator and see if the problem goes away. I might try the following item before I go that route

http://www.zzperformance.com/grand_p...7931331a540383

[BNaylor]

The Delcotron CS130 (105 amp) series alternators are pretty reliable and there are no really no inherent problems or issues. Issues may arise when you overload the system with an aftermarket stereo system and amp or other accessories to include aftermarket head lamps and/or a bonifide electrical problem. If it is an alternator issue that is because it has a problem or worn out - rotor, stator, diodes or voltage regulator. Using that voltage booster is not intended to be used to compensate for a bad alternator.

Best thing to do is measure and monitor the alternator output with a DMM at idle and see if it is in specs. At least 13 volts to around 14.5 volts. Check it under load and without load.

[Den69RS96]

My car has had the flickering headlights since it was new. Its bone stock in terms of electronics. I have taken my car to the two different dealerships numerous times and they never could find the problem. I even went to two different dealerships. My dads Olds does the same thing. The dealer he went to said it was voltage fluctuation from the alternator and that switching the alternator may or may not help. From what I've heard this is fairly common problem on gm midsize cars. I checked my alternator at idle and its voltage is normal.

It's hard to test the voltage when it happens because it only occurs when driving. If I let of the gas pedal a coast for a moment or two the head lights and sometimes the dash flickers. It does it on the highway or side streets. Once your back in to the throttle, it usually goes away once the engine rpm stablizes.

[guitarfish]

Yep, what Den69RS96 wrote is EXACTLY what happens with mine. It's never been a major issue, nor a safety issue, so I'm not surprised there's never been a recall for it. I'd like it fixed. I have 158,000 miles, so my alt could die any day, LOL.

[BNaylor]

Well about the only thing in common here is both of you have 2002 models. I agree you guys have a problem but where I disagree is whether it is a common, design or inherent problem. Probably more of an idiosyncracy type problem which may or may not have a solution. I have 3 GM "W" body cars and none have the problem described and they span model years '97 - '01. And I have worked with alot of Grand Prixs through the years.

Now on my GTP I replaced the ignition switch about 4 years ago due to flickering headlamps, IP and DIC. It started with just the DIC acting up and eventually the DIC crapped out. Replaced the DIC and the flickering was still there. After extensive troubleshooting came up with the ignition switch. I disassembled the old one and several contacts were carboned up and arced out.

If your problem is a component and not some weird problem like bad grounding the most likely cause would be either the ignition switch and/or the multifunction switch. The circuits can be troubleshot with proper documentation like a FSM.

BTW - The problem is not going to fix itself. You are going to have to go through the process of illimination/troubleshooting which may include replacing the alternator first.

[Den69RS96]

I never thought the ignition switch could possibly cause this. Electrical issues are somthing I usually stay away from given how frustrating it can be to find them. If I begin to have other electical issues, I'll check the switch out. Thanks for info.

[BNaylor]

Originally Posted by Den69RS96

I never thought the ignition switch could possibly cause this. Electrical issues are somthing I usually stay away from given how frustrating it can be to find them. If I begin to have other electical issues, I'll check the switch out. Thanks for info.

The ignition switch is just one possibility but normally there are other symptoms. Finding electrical problems is like looking for a needle in a haystack. Look for other symptoms like DRL, HVAC blower acting up, no rear defog, no cruise control or dropping out, DIC, etc.

Also, I would not rule out the multifunction switch (MFS) if your problem is just the headlamp flicker. The contacts in the MFS suffer the same condition as an ignition switch. The low and high beam voltages pass right through it and the bad part is there is no relay to protect the circuit. The MFS gets the full load (high current) without a relay as a buffer. The MFS is a common failure item.

[Den69RS96]

Thanks again. I'll check out the MFS. I'm replacing the struts on the car and changing the plugs and wires within the next few weeks if it warms up. If the MFS is not expensive, I'll replace it and see if that helps. All these normal maintainence items are cutting into the budget for the forged rotating assembly I plan to buy for the small block in my 69 camaro